Network Working Group P. Calhoun, Editor
Internet-Draft Cisco Systems, Inc.
Expires: November 6, 2006 M. Montemurro, Editor
Chantry Networks
D. Stanley, Editor
Aruba Networks
May 5, 2006
CAPWAP Protocol Specification
draft-ietf-capwap-protocol-specification-01
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Wireless LAN product architectures have evolved from single
autonomous access points to systems consisting of a centralized
controller and Wireless Termination Points (WTPs). The general goal
of centralized control architectures is to move access control,
including user authentication and authorization, mobility management
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and radio management from the single access point to a centralized
controller.
This specification defines the Control And Provisioning of Wireless
Access Points (CAPWAP) Protocol. The CAPWAP protocol meets the IETF
CAPWAP working group protocol requirements. The CAPWAP protocol is
designed to be flexible, allowing it to be used for a variety of
wireless technologies. This document describes the base CAPWAP
protocol, including an extension which supports the IEEE 802.11
wireless LAN protocol. Future extensions will enable support of
additional wireless technologies.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Conventions used in this document . . . . . . . . . . . 8
1.3. Contributing Authors . . . . . . . . . . . . . . . . . . 8
1.4. Acknowledgements . . . . . . . . . . . . . . . . . . . . 10
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11
2.1. Wireless Binding Definition . . . . . . . . . . . . . . 12
2.2. CAPWAP Session Establishment Overview . . . . . . . . . 12
2.3. CAPWAP State Machine Definition . . . . . . . . . . . . 14
2.3.1. CAPWAP Protocol State Transitions . . . . . . . . . 15
2.3.2. CAPWAP to DTLS Commands . . . . . . . . . . . . . . 22
2.3.3. DTLS to CAPWAP Notifications . . . . . . . . . . . 23
2.3.4. DTLS State Transitions . . . . . . . . . . . . . . 23
2.4. Use of DTLS in the CAPWAP Protocol . . . . . . . . . . . 26
2.4.1. DTLS Handshake Processing . . . . . . . . . . . . . 27
2.4.2. DTLS Error Handling . . . . . . . . . . . . . . . . 28
2.4.3. DTLS Rehandshake Behavior . . . . . . . . . . . . . 29
2.4.4. DTLS EndPoint Authentication . . . . . . . . . . . 32
3. CAPWAP Transport . . . . . . . . . . . . . . . . . . . . . . 35
3.1. UDP Transport . . . . . . . . . . . . . . . . . . . . . 35
3.2. AC Discovery . . . . . . . . . . . . . . . . . . . . . . 35
3.3. Fragmentation/Reassembly . . . . . . . . . . . . . . . . 36
4. CAPWAP Packet Formats . . . . . . . . . . . . . . . . . . . . 37
4.1. CAPWAP Transport Header . . . . . . . . . . . . . . . . 38
4.2. CAPWAP Data Messages . . . . . . . . . . . . . . . . . . 40
4.3. CAPWAP Control Messages . . . . . . . . . . . . . . . . 41
4.3.1. Control Message Format . . . . . . . . . . . . . . 41
4.3.2. Control Message Quality of Service . . . . . . . . 44
4.4. CAPWAP Protocol Message Elements . . . . . . . . . . . . 44
4.4.1. AC Descriptor . . . . . . . . . . . . . . . . . . . 45
4.4.2. AC IPv4 List . . . . . . . . . . . . . . . . . . . 46
4.4.3. AC IPv6 List . . . . . . . . . . . . . . . . . . . 46
4.4.4. AC Name . . . . . . . . . . . . . . . . . . . . . . 47
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4.4.5. AC Name with Index . . . . . . . . . . . . . . . . 47
4.4.6. AC Timestamp . . . . . . . . . . . . . . . . . . . 48
4.4.7. Add MAC ACL Entry . . . . . . . . . . . . . . . . . 48
4.4.8. Add Mobile Station . . . . . . . . . . . . . . . . 49
4.4.9. Add Static MAC ACL Entry . . . . . . . . . . . . . 49
4.4.10. CAPWAP Timers . . . . . . . . . . . . . . . . . . . 50
4.4.11. Change State Event . . . . . . . . . . . . . . . . 50
4.4.12. Data Transfer Data . . . . . . . . . . . . . . . . 51
4.4.13. Data Transfer Mode . . . . . . . . . . . . . . . . 52
4.4.14. Decryption Error Report . . . . . . . . . . . . . . 52
4.4.15. Decryption Error Report Period . . . . . . . . . . 53
4.4.16. Delete MAC ACL Entry . . . . . . . . . . . . . . . 53
4.4.17. Delete Mobile Station . . . . . . . . . . . . . . . 54
4.4.18. Delete Static MAC ACL Entry . . . . . . . . . . . . 54
4.4.19. Discovery Type . . . . . . . . . . . . . . . . . . 55
4.4.20. Duplicate IPv4 Address . . . . . . . . . . . . . . 55
4.4.21. Duplicate IPv6 Address . . . . . . . . . . . . . . 56
4.4.22. Idle Timeout . . . . . . . . . . . . . . . . . . . 56
4.4.23. Image Data . . . . . . . . . . . . . . . . . . . . 57
4.4.24. Image Filename . . . . . . . . . . . . . . . . . . 57
4.4.25. Initiate Download . . . . . . . . . . . . . . . . . 58
4.4.26. Location Data . . . . . . . . . . . . . . . . . . . 58
4.4.27. MTU Discovery Padding . . . . . . . . . . . . . . . 59
4.4.28. Radio Administrative State . . . . . . . . . . . . 59
4.4.29. Result Code . . . . . . . . . . . . . . . . . . . . 60
4.4.30. Session ID . . . . . . . . . . . . . . . . . . . . 60
4.4.31. Statistics Timer . . . . . . . . . . . . . . . . . 61
4.4.32. Vendor Specific Payload . . . . . . . . . . . . . . 61
4.4.33. WTP Board Data . . . . . . . . . . . . . . . . . . 62
4.4.34. WTP Descriptor . . . . . . . . . . . . . . . . . . 63
4.4.35. WTP Fallback . . . . . . . . . . . . . . . . . . . 64
4.4.36. WTP Frame Encapsulation Type . . . . . . . . . . . 65
4.4.37. WTP IPv4 IP Address . . . . . . . . . . . . . . . . 66
4.4.38. WTP MAC Type . . . . . . . . . . . . . . . . . . . 66
4.4.39. WTP Radio Information . . . . . . . . . . . . . . . 67
4.4.40. WTP Manager Control IPv4 Address . . . . . . . . . 67
4.4.41. WTP Manager Control IPv6 Address . . . . . . . . . 68
4.4.42. WTP Name . . . . . . . . . . . . . . . . . . . . . 69
4.4.43. WTP Reboot Statistics . . . . . . . . . . . . . . . 69
4.4.44. WTP Static IP Address Information . . . . . . . . . 70
4.5. CAPWAP Protocol Timers . . . . . . . . . . . . . . . . . 71
4.5.1. DiscoveryInterval . . . . . . . . . . . . . . . . . 71
4.5.2. DTLSRehandshake . . . . . . . . . . . . . . . . . . 71
4.5.3. DTLSSessionDelete . . . . . . . . . . . . . . . . . 71
4.5.4. EchoInterval . . . . . . . . . . . . . . . . . . . 71
4.5.5. KeyLifetime . . . . . . . . . . . . . . . . . . . . 71
4.5.6. MaxDiscoveryInterval . . . . . . . . . . . . . . . 72
4.5.7. NeighborDeadInterval . . . . . . . . . . . . . . . 72
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4.5.8. ResponseTimeout . . . . . . . . . . . . . . . . . . 72
4.5.9. RetransmitInterval . . . . . . . . . . . . . . . . 72
4.5.10. SilentInterval . . . . . . . . . . . . . . . . . . 72
4.5.11. WaitJoin . . . . . . . . . . . . . . . . . . . . . 72
4.6. CAPWAP Protocol Variables . . . . . . . . . . . . . . . 73
4.6.1. DiscoveryCount . . . . . . . . . . . . . . . . . . 73
4.6.2. MaxDiscoveries . . . . . . . . . . . . . . . . . . 73
4.6.3. MaxRetransmit . . . . . . . . . . . . . . . . . . . 73
4.6.4. RetransmitCount . . . . . . . . . . . . . . . . . . 73
5. CAPWAP Discovery Operations . . . . . . . . . . . . . . . . . 74
5.1. Discovery Request Message . . . . . . . . . . . . . . . 74
5.2. Discovery Response Message . . . . . . . . . . . . . . . 75
5.3. Primary Discovery Request Message . . . . . . . . . . . 75
5.4. Primary Discovery Response . . . . . . . . . . . . . . . 76
6. CAPWAP Join Operations . . . . . . . . . . . . . . . . . . . 77
6.1. Join Request . . . . . . . . . . . . . . . . . . . . . . 77
6.2. Join Response . . . . . . . . . . . . . . . . . . . . . 78
7. Control Channel Management . . . . . . . . . . . . . . . . . 79
7.1. Echo Request . . . . . . . . . . . . . . . . . . . . . . 79
7.2. Echo Response . . . . . . . . . . . . . . . . . . . . . 79
8. WTP Configuration Management . . . . . . . . . . . . . . . . 80
8.1. Configuration Consistency . . . . . . . . . . . . . . . 80
8.1.1. Configuration Flexibility . . . . . . . . . . . . . 81
8.2. Configuration Status . . . . . . . . . . . . . . . . . . 81
8.3. Configuration Status Response . . . . . . . . . . . . . 82
8.4. Configuration Update Request . . . . . . . . . . . . . . 82
8.5. Configuration Update Response . . . . . . . . . . . . . 83
8.6. Change State Event Request . . . . . . . . . . . . . . . 84
8.7. Change State Event Response . . . . . . . . . . . . . . 84
8.8. Clear Config Indication . . . . . . . . . . . . . . . . 85
9. Device Management Operations . . . . . . . . . . . . . . . . 86
9.1. Image Data Request . . . . . . . . . . . . . . . . . . . 86
9.2. Image Data Response . . . . . . . . . . . . . . . . . . 87
9.3. Reset Request . . . . . . . . . . . . . . . . . . . . . 87
9.4. Reset Response . . . . . . . . . . . . . . . . . . . . . 87
9.5. WTP Event Request . . . . . . . . . . . . . . . . . . . 87
9.6. WTP Event Response . . . . . . . . . . . . . . . . . . . 88
9.7. Data Transfer Request . . . . . . . . . . . . . . . . . 88
9.8. Data Transfer Response . . . . . . . . . . . . . . . . . 88
10. Mobile Session Management . . . . . . . . . . . . . . . . . . 90
10.1. Mobile Config Request . . . . . . . . . . . . . . . . . 90
10.2. Mobile Config Response . . . . . . . . . . . . . . . . . 90
11. IEEE 802.11 Binding . . . . . . . . . . . . . . . . . . . . . 91
11.1. Split MAC and Local MAC Functionality . . . . . . . . . 91
11.1.1. Split MAC . . . . . . . . . . . . . . . . . . . . . 91
11.1.2. Local MAC . . . . . . . . . . . . . . . . . . . . . 93
11.2. Roaming Behavior . . . . . . . . . . . . . . . . . . . . 96
11.3. Group Key Refresh . . . . . . . . . . . . . . . . . . . 97
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11.4. Transport specific bindings . . . . . . . . . . . . . . 97
11.5. BSSID to WLAN ID Mapping . . . . . . . . . . . . . . . . 99
11.6. Quality of Service for Control Messages . . . . . . . . 99
11.7. IEEE 802.11 Specific CAPWAP Control Messages . . . . . . 100
11.7.1. IEEE 802.11 WLAN Config Request . . . . . . . . . . 100
11.7.2. IEEE 802.11 WLAN Config Response . . . . . . . . . 101
11.8. Data Message bindings . . . . . . . . . . . . . . . . . 101
11.9. Control Message bindings . . . . . . . . . . . . . . . . 101
11.9.1. Mobile Config Request . . . . . . . . . . . . . . . 101
11.9.2. WTP Event Request . . . . . . . . . . . . . . . . . 101
11.9.3. Configuration Messages . . . . . . . . . . . . . . 102
11.10. IEEE 802.11 Message Element Definitions . . . . . . . . 102
11.10.1. IEEE 802.11 Add WLAN . . . . . . . . . . . . . . . 102
11.10.2. IEEE 802.11 Antenna . . . . . . . . . . . . . . . . 106
11.10.3. IEEE 802.11 Assigned WTP BSSID . . . . . . . . . . 107
11.10.4. IEEE 802.11 Broadcast Probe Mode . . . . . . . . . 108
11.10.5. IEEE 802.11 Delete WLAN . . . . . . . . . . . . . . 108
11.10.6. IEEE 802.11 Direct Sequence Control . . . . . . . . 109
11.10.7. IEEE 802.11 Information Element . . . . . . . . . . 110
11.10.8. IEEE 802.11 MAC Operation . . . . . . . . . . . . . 110
11.10.9. IEEE 802.11 MIC Countermeasures . . . . . . . . . . 112
11.10.10. IEEE 802.11 MIC Error Report From Mobile . . . . . 112
11.10.11. IEEE 802.11 Mobile . . . . . . . . . . . . . . . . 113
11.10.12. IEEE 802.11 Mobile Session Key . . . . . . . . . . 114
11.10.13. IEEE 802.11 Multi-domain Capability . . . . . . . . 116
11.10.14. IEEE 802.11 OFDM Control . . . . . . . . . . . . . 117
11.10.15. IEEE 802.11 Rate Set . . . . . . . . . . . . . . . 118
11.10.16. IEEE 802.11 Statistics . . . . . . . . . . . . . . 118
11.10.17. IEEE 802.11 Supported Rates . . . . . . . . . . . . 120
11.10.18. IEEE 802.11 Tx Power . . . . . . . . . . . . . . . 121
11.10.19. IEEE 802.11 Tx Power Level . . . . . . . . . . . . 121
11.10.20. IEEE 802.11 Update Mobile QoS . . . . . . . . . . . 122
11.10.21. IEEE 802.11 Update WLAN . . . . . . . . . . . . . . 122
11.10.22. IEEE 802.11 WTP Quality of Service . . . . . . . . 125
11.10.23. IEEE 802.11 WTP Radio Fail Alarm Indication . . . . 126
11.10.24. IEEE 802.11 WTP Radio Configuration . . . . . . . . 127
11.10.25. Station QoS Profile . . . . . . . . . . . . . . . . 128
11.11. Technology Specific Message Element Values . . . . . . . 129
12. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 130
13. Security Considerations . . . . . . . . . . . . . . . . . . . 132
13.1. CAPWAP Security . . . . . . . . . . . . . . . . . . . . 132
13.1.1. Converting Protected Data into Unprotected Data . . 133
13.1.2. Converting Unprotected Data into Protected Data
(Insertion) . . . . . . . . . . . . . . . . . . . . 133
13.1.3. Deletion of Protected Records . . . . . . . . . . . 133
13.1.4. Insertion of Unprotected Records . . . . . . . . . 133
13.2. Use of Preshared Keys in CAPWAP . . . . . . . . . . . . 133
13.3. Use of Certificates in CAPWAP . . . . . . . . . . . . . 134
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13.4. AAA Security . . . . . . . . . . . . . . . . . . . . . . 134
13.5. IEEE 802.11 Security . . . . . . . . . . . . . . . . . . 135
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 136
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 137
15.1. Normative References . . . . . . . . . . . . . . . . . . 137
15.2. Informational References . . . . . . . . . . . . . . . . 138
Editors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 140
Intellectual Property and Copyright Statements . . . . . . . . . 141
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1. Introduction
The emergence of centralized architectures, in which simple IEEE
802.11 WTPs are managed by an Access Controller (AC) suggests that a
standards based, interoperable protocol could radically simplify the
deployment and management of wireless networks. WTPs require a set
of dynamic management and control functions related to their primary
task of connecting the wireless and wired mediums. Traditional
protocols for managing WTPs are either manual static configuration
via HTTP, proprietary Layer 2 specific or non-existent (if the WTPs
are self-contained). This document describes the CAPWAP Protocol, a
standard, interoperable protocol which enables an AC to manage a
collection of WTPs. While the protocol is defined to be independent
of layer 2 technology, an IEEE 802.11 binding is provided to support
IEEE 802.11 wireless LAN networks.
CAPWAP assumes a network configuration consisting of multiple WTPs
communicating via the Internet Protocol (IP) to an AC. WTPs are
viewed as remote RF interfaces controlled by the AC. The AC forwards
all L2 frames to be transmitted by a WTP to that WTP via the CAPWAP
protocol. L2 frames from mobile nodes (STAs) are forwarded by the
WTP to the AC using the CAPWAP protocol. Both Split-MAC and Local
MAC arhcitectures are supported. Figure 1 illustrates this
arrangement as applied to an IEEE 802.11 binding.
+-+ 802.11 frames +-+
| |--------------------------------| |
| | +-+ | |
| |--------------| |---------------| |
| | 802.11 PHY/ | | CAPWAP | |
| | MAC sublayer | | | |
+-+ +-+ +-+
STA WTP AC
Figure 1: Representative CAPWAP Architecture for Split MAC
Provisioning WTPs with security credentials, and managing which WTPs
are authorized to provide service are traditionally handled by
proprietary solutions. Allowing these functions to be performed from
a centralized AC in an interoperable fashion increases manageability
and allows network operators to more tightly control their wireless
network infrastructure.
1.1. Goals
The goals for the CAPWAP protocol are listed below:
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1. To centralize the bridging, forwarding, authentication and policy
enforcement functions for a wireless network. Optionally, the AC
may also provide centralized encryption of user traffic.
Centralization of these functions will enable reduced cost and
higher efficiency by applying the capabilities of network
processing silicon to the wireless network, as in wired LANs.
2. To enable shifting of the higher level protocol processing from
the WTP. This leaves the time critical applications of wireless
control and access in the WTP, making efficient use of the
computing power available in WTPs which are the subject to severe
cost pressure.
3. To provide a generic encapsulation and transport mechanism,
enabling the CAPWAP protocol to be applied to other access point
types in the future, via a specific wireless binding.
The CAPWAP protocol concerns itself solely with the interface between
the WTP and the AC. Inter-AC, or mobile node (STA) to AC
communication is strictly outside the scope of this document.
1.2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
1.3. Contributing Authors
This section lists and acknowledges the authors of significant text
and concepts included in this specification. [Note: This section
needs work to accurately reflect the contribution of each author and
this work will be done in revision 01 of this document.]
The CAPWAP Working Group selected the Lightweight Access Point
Protocol (LWAPP) [add reference, when available]to be used as the
basis of the CAPWAP protocol specification. The following people are
authors of the LWAPP document:
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Bob O'Hara, Cisco Systems, Inc.,170 West Tasman Drive, San Jose, CA 95134
Phone: +1 408-853-5513, Email: bob.ohara@cisco.com
Pat Calhoun, Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134
Phone: +1 408-853-5269, Email: pcalhoun@cisco.com
Rohit Suri, Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134
Phone: +1 408-853-5548, Email: rsuri@cisco.com
Nancy Cam Winget, Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134
Phone: +1 408-853-0532, Email: ncamwing@cisco.com
Scott Kelly, Aruba Networks, 1322 Crossman Ave, Sunnyvale, CA 94089
Phone: +1 408-754-8408, Email: skelly@arubanetworks.com
Michael Glenn Williams, Nokia, Inc., 313 Fairchild Drive, Mountain View, CA 94043
Phone: +1 650-714-7758, Email: Michael.G.Williams@Nokia.com
Sue Hares, Nexthop Technologies, Inc., 825 Victors Way, Suite 100, Ann Arbor, MI 48108
Phone: +1 734 222 1610, Email: shares@nexthop.com
DTLS is used as the security solution for the CAPWAP protocol. The
following people are authors of significant DTLS-related text
included in this document:
Scott Kelly, Aruba Networks, 1322 Crossman Ave, Sunnyvale, CA 94089
Phone: +1 408-754-8408, Email: skelly@arubanetworks.com
Eric Rescorla, Network Resonance, 2483 El Camino Real, #212,Palo Alto CA, 94303
Email: ekr@networkresonance.com
The concept of using DTLS to secure the CAPWAP protocol was part of
the Secure Light Access Point Protocol (SLAPP) proposal [add
reference when available]. The following people are authors of the
SLAPP proposal:
Partha Narasimhan, Aruba Networks, 1322 Crossman Ave, Sunnyvale, CA 94089
Phone: +1 408-480-4716, Email: partha@arubanetworks.com
Dan Harkins, Tropos Networks, 555 Del Rey Avenue, Sunnyvale, CA, 95085
Phone: +1 408 470 7372, Email: dharkins@tropos.com
Subbu Ponnuswamy, Aruba Networks, 1322 Crossman Ave, Sunnyvale, CA 94089
Phone: +1 408-754-1213, Email: subbu@arubanetworks.com
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1.4. Acknowledgements
The authors thank Michael Vakulenko for contributing text that
describes how CAPWAP can be used over a layer 3 (IP/UDP) network.
The authors thank Russ Housley and Charles Clancy for their
assistance in provide a security review of the LWAPP specification.
Charles' review can be found at [16].
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2. Protocol Overview
The CAPWAP protocol is a generic protocol defining AC and WTP control
and data plane communication via a CAPWAP protocol transport
mechanism. CAPWAP control messages, and optionally CAPWAP data
messages, are secured using Datagram Transport Layer Security (DTLS)
[14]. DTLS is a standards-track IETF protocol based upon TLS. The
underlying security-related protocol mechanisms of TLS have been
successfully deployed for many years.
The CAPWAP protocol Transport layer carries two types of payload,
CAPWAP Data messages and CAPWAP Control messages. CAPWAP Data
messages are forwarded wireless frames. CAPWAP protocol Control
messages are management messages exchanged between a WTP and an AC.
The CAPWAP Data and Control packets are sent over separate UDP ports.
Since both data and control frames can exceed the PMTU, the payload
of a CAPWAP data or control message can be fragmented. The
fragmentation behavior is defined in Section 3.
The CAPWAP Protocol begins with a discovery phase. The WTPs send a
Discovery Request message, causing any Access Controller (AC)
receiving the message to respond with a Discovery Response message.
From the Discovery Response messages received, a WTP will select an
AC with which to establish a secure DTLS session. CAPWAP protocol
messages will be fragmented to the maximum length discovered to be
supported by the network.
Once the WTP and the AC have completed DTLS session establishment, a
configuration exchange occurs in which both devices to agree on
version information. During this exchange the WTP may receive
provisioning settings. For the IEEE 802.11 binding, this information
typically includes a name (IEEE 802.11 Service Set Identifier, SSID)
security parameters, the data rates to be advertised and the
associated radio channel(s) to be used. The WTP is then enabled for
operation.
When the WTP and AC have completed the version and provision exchange
and the WTP is enabled, the CAPWAP protocol is used to encapsulate
the wireless data frames sent between the WTP and AC. The CAPWAP
protocol will fragment the L2 frames if the size of the encapsulated
wireless user data (Data) or protocol control (Management) frames
causes the resulting CAPWAP protocol packet to exceed the MTU
supported between the WTP and AC. Fragmented CAPWAP packets are
reassembled to reconstitute the original encapsulated payload.
The CAPWAP protocol provides for the delivery of commands from the AC
to the WTP for the management of mobile units (STAs) that are
communicating with the WTP. This may include the creation of local
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data structures in the WTP for the mobile units and the collection of
statistical information about the communication between the WTP and
the mobile units. The CAPWAP protocol provides a mechanism for the
AC to obtain statistical information collected by the WTP.
The CAPWAP protocol provides for a keep alive feature that preserves
the communication channel between the WTP and AC. If the AC fails to
appear alive, the WTP will try to discover a new AC.
This Document uses terminology defined in [5].
2.1. Wireless Binding Definition
The CAPWAP protocol is independent of a specific WTP radio
technology. Elements of the CAPWAP protocol are designed to
accommodate the specific needs of each wireless technology in a
standard way. Implementation of the CAPWAP protocol for a particular
wireless technology must follow the binding requirements defined for
that technology. This specification includes a binding for the IEEE
802.11 standard(see Section 11).
When defining a binding for other wireless technologies, the authors
MUST include any necessary definitions for technology-specific
messages and all technology-specific message elements for those
messages. At a minimum, a binding MUST provide the definition for a
binding-specific Statistics message element, carried in the WTP Event
Request message, and a Mobile message element, carried in the Mobile
Configure Request. If technology specific message elements are
required for any of the existing CAPWAP messages defined in this
specification, they MUST also be defined in the technology binding
document.
The naming of binding-specific message elements MUST begin with the
name of the technology type, e.g., the binding for IEEE 802.11,
provided in this specification, begins with "IEEE 802.11"."
2.2. CAPWAP Session Establishment Overview
This section describes the session establishment process message
exchanges in the ideal case. The annotated ladder diagram shows the
AC on the right, the WTP on the left, and assumes the use of
certificates for DTLS authentication. The CAPWAP Protocol State
Machine is described in detail in Section 2.3.
============ ============
WTP AC
============ ============
[----------- begin optional discovery ------------]
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Discover Request ------>
<------ Discover Response
[----------- end optional discovery ------------]
(--- begin dtls handshake ---)
ClientHello ------>
<------ HelloVerifyRequest
(with cookie)
ClientHello ------>
(with cookie)
<------ ServerHello
<------ Certificate
<------ ServerHelloDone
(WTP callout for AC authorization)
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ------>
(AC callout for WTP
authorization)
[ChangeCipherSpec]
<------ Finished
(--- DTLS session is established now ---)
Join Request ------>
<------ Join Response
( ---assume image is up to date ---)
Configure Request ------->
<------ Configure Response
(--- enter RUN state ---)
:
:
Echo Request ------->
<------ Echo Response
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:
:
EventRequest ------->
<------ Event Response
:
:
At the end of the illustrated CAPWAP message exchange, the AC and WTP
are securely exchanging CAPWAP control messages. This is an
idealized illustration, provided to clarify protocol operation.
Section 2.3 provides a detailed description of the corresponding
state machine.
2.3. CAPWAP State Machine Definition
The following state diagram represents the lifecycle of a WTP-AC
session. Use of DTLS by the CAPWAP protocol results in the
juxtaposition of two nominally separate yet tightly bound state
machines. The DTLS and CAPWAP state machines are coupled through an
API consisting of commands (from CAPWAP to DTLS) and notifications
(from (DTLS to CAPWAP). Certain transitions in the DTLS state
machine are triggered by commands from the CAPWAP state machine,
while certain transitions in the CAPWAP state machine are triggered
by notifications from the DTLS state machine.
This section defines the CAPWAP Integrated State Machine. In the
figure below, single lines (denoted with '-' and '|') are used to
illustrate state transitions. Double lines (denoted with '=' and
'"') are used to illustrate commands and notifications between DTLS
and CAPWAP. A line composed of '~' characters is used to delineate
the boundary between nominal CAPWAP and DTLS state machine
components.
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/-------------<----------------+--------------------\
v |d |
+------+ b+-----------+ +----------+ |
| Idle |-->| Discovery |--->| Sulking | |
+------+ a +-----------+ c +----------+ |
^ |aa ^ |e /----------------------\ |
| V f| v k| | |
h +--------------+ +------------+ i +------------+j | |
/--| Join |->| Configure |-->| Image Data | | |
| +--------------+ g+------------+ +------------+ | |
| "c1, ^ ^ ^ m| ^ |l | |
| "c4 " " " | /-------/ | /----/ |
| " " " " V |s v V |
| " " " " +------------+ o+------------+ |
| " " " " | Run |->| Reset |-------/
| " " " " n+------------+ +------------+ p
| " " " " "c2 ^ ^ c3" ^
\---"-----"--"---"--------"----"-------/ " " CAPWAP
~~~~~~~"~~~~~"~~"~~~"~~~~~~~~"~~~~"~~~~~~~~~~~~"~~~"~~~~~~~~~~~~
" " " " " " " " DTLS
v " "n2 \"""""\ " " v "n6,n7
/-->+------+ " W+------+ " " " +------------+
| /-| Idle | " C| Auth |--"~-"----"----->| Shutdown |-------\P
| | +------+ " +------+V " " " /--->| |<----\ |
| |X Z| " ^ U| " " n4 " | +------------+ | |
| | | " | | " " n5," | ^ | |
| | v "n1 |Y | n3" v n8" |R |Q | |
| | +--------+ | +------------+ S+------------+ | |
| | | Init | \->| Run |<--| Rekey | | |
| | +--------+ | |-->| | | |
| | +------------+T +------------+ | |
| \---------------------------------------------------------/ |
\-------------------------------------------------------------/
Figure 2: CAPWAP Integrated State Machine
The CAPWAP protocol state machine, depicted above, is used by both
the AC and the WTP. In cases where states are not shared (i.e. not
implemented in one or the other of the AC or WTP), this is explicitly
called out in the transition descriptions below. For every state
defined, only certain messages are permitted to be sent and received.
The CAPWAP control messages definitions specify the state(s) in which
each message is valid.
2.3.1. CAPWAP Protocol State Transitions
The following text discusses the various state transitions, and the
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events that cause them. This section does not discuss interactions
between DTLS- and CAPWAP-specific states. Those interactions, as
well as DTLS-specific states and transitions, are discussed in
subsequent sections.
Idle to Discovery (a): This transition occurs once device
initialization is complete.
WTP: The WTP enters the Discovery state prior to transmitting the
first Discovery Request message (see Section 5.1). Upon
entering this state, the WTP sets the DiscoveryInterval timer
(see Section 4.5). The WTP resets the DiscoveryCount counter
to zero (0) (see Section 4.6). The WTP also clears all
information from ACs it may have received during a previous
Discovery phase.
AC: The AC does not maintain state information for the WTP upon
reception of the Discovery Request message, but it SHOULD
respond with a Discovery Response message (see Section 5.2).
This transition is a no-op for the AC.
Idle to Join (aa): This transition occurs when the WTP presents a
DTLS ClientHello message containing a valid cookie to the AC.
WTP: This transition is a no-op for the WTP.
AC: The AC does not maintain state information until the WTP
presents a DTLS ClientHello message containing a valid cookie.
Upon receipt of a DTLS ClientHello message containing a valid
cookie, the AC creates session state and transitions to the
Join state.
Discovery to Discovery (b): In the Discovery state, the WTP
determines which AC to connect to.
WTP: This transition occurs when the DiscoveryInterval timer
expires. If the WTP is configured with a list of ACs, it
transmits a Discovery Request message to every AC from which it
has not received a Discovery Response message. For every
transition to this event, the WTP increments the DiscoveryCount
counter. See Section 5.1 for more information on how the WTP
knows the ACs to which it should transmit the Discovery Request
messages. The WTP restarts the DiscoveryInterval timer
whenever it transmits Discovery Request messages.
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AC: This is a no-op.
Discovery to Sulking (c): This transition occurs on a WTP when
Discovery or connectivity to the AC fails.
WTP: The WTP enters this state when the DiscoveryInterval timer
expires and the DiscoveryCount variable is equal to the
MaxDiscoveries variable (see Section 4.6). Upon entering this
state, the WTP shall start the SilentInterval timer. While in
the Sulking state, all received CAPWAP protocol messages
received shall be ignored.
AC: This is a no-op.
Sulking to Idle (d): This transition occurs on a WTP when it must
restart the discovery phase.
WTP: The WTP enters this state when the SilentInterval timer (see
Section 4.5) expires.
AC: This is a no-op.
Discovery to Join (e): This transition occurs when the WTP sends a
ClientHello message to the AC, confirming that it wishes to be
provided services by the AC.
WTP: The WTP selects the best AC based either on information it
gathered during the Discovery Phase or on its configuration.
It then sends a JoinRequest message to its preferred AC, sets
the WaitJoin timer, and awaits the Join Response Message.
AC: This is a no-op for the AC.
Join to Discovery (f): This state transition is used to return the
WTP to the Discovery state when an unresponsive AC is encountered.
WTP: The WTP re-enters the Discovery state when the WaitJoin timer
expires.
AC: This is a no-op.
Join to Configure (g): This state transition is used by the WTP and
the AC to exchange configuration information.
WTP: The WTP enters the Configure state when it successfully
completes the Join operation. If it determines that its
version number and the version number advertised by the AC are
the same, the WTP transmits the Configuration Status message
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(see Section 8.2) to the AC with a snapshot of its current
configuration. The WTP also starts the ResponseTimeout timer
(see ). (Section 4.5) If the version numbers are not the same,
the WTP will immediately transition to Image Data state (see
transition (i)).
AC: This state transition occurs immediately after the AC
transmits the Join Response message to the WTP. If the AC
receives the Configuration Status message from the WTP, the AC
must transmit a Configuration Status Response message(see
Section 8.3) to the WTP, and may include specific message
elements to override the WTP's configuration. If the AC
instead receives the Image Data Request from the WTP, it
immediately transitions to the Image Data state (see transition
(i)).
Join to Reset (h): This state transition occurs when the WaitJoin
Timer expires.
WTP: The state transition occurs when the WTP WaitJoin timer
expires, or upon DTLS negotiation failure.
AC: Thise state transition occurs when the AC WaitJoin timer
expires, or or upon DTLS negotiation failure.
Configure to Image Data (i): This state transition is used by the WTP
and the AC to download executable firmware.
WTP: The WTP enters the Image Data state when it successfully
comletes DTLS session establishment, and determines that its
version number and the version number advertised by the AC are
different. The WTP transmits the Image Data Request (see
Section 9.1) message requesting that a download of the AC's
latest firmware be initiated.
AC: This state transition occurs when the AC receives the Image
Data Request message from the WTP. The AC must transmit an
Image Data Response message (see Section 9.2) to the WTP, which
includes a portion of the firmware.
Image Data to Image Data (j): The Image Data state is used by WTP and
the AC during the firmware download phase.
WTP: The WTP enters the Image Data state when it receives an Image
Data Response message indicating that the AC has more data to
send.
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AC: This state transition occurs when the AC receives the Image
Data Request message from the WTP while already in the Image
Data state, and it detects that the firmware download has not
completed.
Configure to Reset (k): This state transition is used to reset the
connection to the AC prior to restarting the WTP with a new
configuration.
WTP: The WTP enters the Reset state when it determines that a
reset of the WTP is required, due to the characteristics of a
new configuration.
AC: The AC transitions to the Reset state when it receives the
DTLSPeerDisconnect (n7) notification.
Image Data to Reset (l): This state transition is used to reset the
DTLS connection prior to restarting the WTP after an image
download.
WTP: When an image download completes, the WTP enters the Reset
state, and terminates the DTLS connection, sending a
DTLSShutdown command to the DTLS state machine.
AC: The AC enters the Reset state upon receipt of a DTLSIdle (n6)
notification.
Configure to Run (m): This state transition occurs when the WTP and
AC enter their normal state of operation.
WTP: The WTP enters this state when it receives a successful
Configuration Status Response message from the AC. The WTP
initializes the HeartBeat timer (see Section 4.5), and
transmits the Change State Event Request message (see
Section 8.6).
AC: This state transition occurs when the AC receives the Change
State Event Request message (see Section 8.6) from the WTP.
The AC responds with a Change State Event Response (see
Section 8.7) message. The AC must start the
NeighborDeadInterval timer (see Section 4.5).
Run to Run (n): This is the normal state of operation.
WTP: This is the WTP's normal state of operation. There are many
events that result this state transition:
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Configuration Update: The WTP receives a Configuration Update
Request message(see Section 8.4). The WTP MUST respond with
a Configuration Update Response message (see Section 8.5).
Change State Event: The WTP receives a Change State Event
Response message, or determines that it must initiate a
Change State Event Request message, as a result of a failure
or change in the state of a radio.
Echo Request: The WTP receives an Echo Request message (see
Section 7.1), to which it MUST respond with an Echo Response
message(see Section 7.2).
Clear Config Indication: The WTP receives a Clear Config
Indication message (see Section 8.8). The WTP MUST reset
its configuration back to manufacturer defaults.
WTP Event: The WTP generates a WTP Event Request message to
send information to the AC (see Section 9.5). The WTP
receives a WTP Event Response message from the AC (see
Section 9.6).
Data Transfer: The WTP generates a Data Transfer Request
message to the AC (see Section 9.7). The WTP receives a
Data Transfer Response message from the AC (see
Section 9.8).
WLAN Config Request: The WTP receives a WLAN Config Request
message (see Section 11.7.1), to which it MUST respond with
a WLAN Config Response message (see Section 11.7.2).
Mobile Config Request: The WTP receives a Mobile Config Request
message (see Section 10.1), to which it MUST respond with a
Mobile Config Response message (see Section 10.2).
AC: This is the AC's normal state of operation:
Configuration Update: The AC sends a Configuration Update
Request message (see Section 8.4) to the WTP to update its
configuration. The AC receives a Configuration Update
Response message (see Section 8.5) from the WTP.
Change State Event: The AC receives a Change State Event
Request message (see Section 8.6), to which it MUST respond
with the Change State Event Response message (see
Section 8.7).
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Echo: The AC sends an Echo Request message Section 7.1 or
receives the corresponding Echo Response message, see
Section 7.2 from the WTP.
Clear Config Indication: The AC sends a Clear Config Indication
message (see Section 8.8).
WLAN Config: The AC sends a WLAN Config Request message (see
Section 11.7.1) or receives the corresponding WLAN Config
Response message (see Section 11.7.2) from the WTP.
Mobile Config: The AC sends a Mobile Config Request message
(see Section 10.1) or receives the corresponding Mobile
Config Response message (see Section 10.2) from the WTP.
Data Transfer: The AC receives a Data Transfer Request message
from the AC (see Section 9.7) and MUST generate a
corresponding Data Transfer Response message (see
Section 9.8).
WTP Event: The AC receives a WTP Event Request message from the
AC (see Section 9.5) and MUST generate a corresponding WTP
Event Response message (see Section 9.6).
Run to Reset(o): This state transition is used when the AC or WTP
wish to tear down the connection. This may occur as part of
normal operation, or due to error conditions.
WTP: The WTP enters the Reset state when it initiates orderly
termination of the DTLS connection, or when the underlying
reliable transport is unable to transmit a message within the
RetransmitInterval timer, see Section 4.5 The WTP also enters
the Reset state upon receiving a DTLS session termination
message (DTLS alert) from the AC. The WTP sends a DTLSReset
command to the DTLS state machine.
AC: The AC enters the Idle state when it initiates orderly
termination of the DTLS connection, or when the underlying
reliable transport is unable to transmit a message within the
RetransmitInterval timer (see Section 4.5), and the maximum
number of RetransmitCount counter has reached the MaxRetransmit
variable (see Section 4.6). The AC also enters the Reset state
upon receiving a DTLS session termination message from the WTP.
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Reset to Idle (p): This state transition occurs when the state
machine is restarted following a system restart, an unrecoverable
error on the AC-WTP connection, or orderly session teardown.
WTP: The WTP clears any state associated with any AC and enters
the Idle state.
AC: The AC clears any state associated with the WTP and enters the
idle state.
Run to Image Data (s): This state transition occurs when the AC
transmits an Image Data Request to the WTP, with the Initiate
Download message element. The means by which the AC decides to
download firmware is undefined, but could occur through an
administrative action.
WTP: The WTP enters this state when it receives an an Image Data
Request to the WTP, with the Initiate Download message element.
The WTP responds by transmitting an Image Data Request with the
Image Filename message element included..
AC: This state transition occurs when the AC decides that an WTP
is to update its firmware by sending an Image Data Request to
the WTP, with the Initiate Download message element.
2.3.2. CAPWAP to DTLS Commands
Four commands are defined for the CAPWAP to DTLS API. These
"commands" are conceptual, and may be implemented as one or more
function calls. This API definition is provided to clarify
interactions between the DTLS and CAPWAP components of the integrated
CAPWAP state machine.
Below is a list of the minimal command API:
o c1: DTLSStart is sent to the DTLS module to cause a DTLS session
to be established.
o c2: DTLSRehandshake is sent to the DTLS module to cause initiation
of a rehandshake (DTLS rekey).
o c3: DTLSShutdown is sent to the DTLS module to cause session
teardown.
o c4: DTLSAbort is sent to the DTLS module to cause session teardown
when the WaitJoin timer expires.
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2.3.3. DTLS to CAPWAP Notifications
Eight notifications are defined for the DTLS to CAPWAP API. These
"notifications" are conceptual, and may be implemented in numerous
ways (e.g. as function return values). This API definition is
provided to clarify interactions between the DTLS and CAPWAP
components of the integrated CAPWAP state machine.
Below is a list of the API notifications:
o n1: DTLSInitFailure is sent to the CAPWAP module to indicate an
initialization failure, which may be due to out of memory or other
internal error condition.
o n2: DTLSAuthenticateFail or DTLSAuthorizeFail is sent to the
CAPWAP module to indicate peer authentication or authorization
failures, respectively.
o n3: DTLSEstablished is sent to the CAPWAP module to indicate that
that a secure channel now exists.
o n4: DTLSEncapFailure may be sent to CAPWAP to indicate an
encapsulation failure. DTLSDecapFailure may be sent to CAPWAP to
indicate an encryption/authentication failure
o n5: DTLSRehandshake is sent to the CAPWAP module to indicate DTLS
rehandshake initiation by peer.
o n6: DTLSIdle is sent to the CAPWAP module to indicate that session
abort (as requested by CAPWAP) is complete; this occurs when the
WaitJoin timer expires, or when CAPWAP is executing an orderly
session shutdown.
o n7: DTLSPeerDisconnect is sent to the CAPWAP module to indicate
DTLS session teardown by peer. Note that the n7 notification, can
be received while in the Join, Configure, Image Data, Run and
Reset states, and always causes a transition to the Reset state.
o n8: DTLSReassemblyFailure may be sent to the CAPWAP module to
indicate DTLS fragment reassembly failure.
2.3.4. DTLS State Transitions
This section describes the transitions in the DTLS-specific portion
of the state machine.
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Idle to Init (Z): This transition indicates the begining of a DTLS
session.
WTP: The state ransition is triggered by receipt of the DTLSStart
command from the CAPWAP state machine, and causes the WTP to
send a DTLS ClientHello to the AC.
AC: The state transition is triggered by receipt of the DTLSStart
command from the CAPWAP state machine. The AC starts the
WaitJoin timer and awaits reception of a DTLS ClientHello
message
Init to Authenticate/Authorize (Y) This transition indicates that the
DTLS handshake is in progress.
WTP: The WTP executes this state transition upon receipt of a
valid ServerHello.
AC: The AC executes this transition upon receipt of a certificate
payload (if configured for public key authentication) or upon
receipt of the ClientKeyExchange payload if configured for
preshared keys.
Init to Idle(X) This state transition occurs upon timeout of the
WaitJoin Timer.
WTP: Upon receiving a DTLSAbort command from the CAPWAP state
machine, the WTP DTLS state machine transitions to Idle state.
AC: Upon receiving a DTLSAbort command from the CAPWAP state
machine, the AC DTLS state machine transitions to Idle state.
Authenticate/Authorize to Authenticate/Authorize (W) This state
transition is a Loopback state, representing execution of the TLS
handshake protocol, including authorization callbacks to the
CAPWAP architecture.
WTP: Upon receiving AC credential, attempt to execute associated
validation, authentication, and authorization callbacks. Note
that credentials may span protocol messages, in which case the
WTP will remain in this state pending receipt of all credential
payloads.
AC: Upon receipt of the WTP credential, attempt to execute
associated validation, authentication, and authorization
callbacks. Note that credentials may span protocol messages,
in which case the AC will remain in this state pending receipt
of all credential payloads.
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Authenticate/Authorize to Shutdown (V) This state transition
indicates a failure of the DTLS handshake.
WTP: Send a DTLSAuthenticateFail or DTLSAuthorizeFail to the
CAPWAP state machine, depending on the exact cause of the
error. May send a DTLS notification to the AC to indicate
failure.
AC: Send a DTLSAuthenticateFail or DTLSAuthorizeFail to the CAPWAP
state machine, depending on the exact cause of the error. May
send a DTLS Notification to the AC to indicate failure.
Authenticate/Authorize to Run (U) This state transition occurs upon
successful completion of the DTLS handshake.
WTP: Send a DTLSEstablished notification to the CAPWAP state
machine.
AC: Send a DTLSEstablished notification to the CAPWAP state
machine.
Run to Rekey (T) This state transition occurs when a DTLS rehandshake
is in progress; this is initiated when either (a) the DTLS state
machine receives the DTLSRehandshake command from CAPWAP, or (b) a
DTLS rehandshake message is received from the peer..
WTP: If CAPWAP issued a DTLSRehandshake command, initiate
rehandshake with the peer; note that control traffic may
continue to flow using existing secure association. If the
rehandshake is initiated by the peer, send a DTLSRehandshake
notification to CAPWAP.
AC: If CAPWAP issued a DTLSRehandshake command, initiate
rehandshake with the peer; note that control traffic may
continue to flow using existing secure association. If the
rehandshake is initiated by the peer, send a DTLSRehandshake
notification to CAPWAP.
Run to Shutdown (S) This state transition indicates a shutdown of the
DTLS channel.
WTP: This state transition occurs when the CAPWAP state machine
sends a DTLSShutdown command, or when the the AC terminates the
DTLS session.
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AC: This state transition occurs when CAPWAP state machine sends a
DTLSShutdown command, or when the WTP terminates the DTLS
session.
Rekey to Run (R) This state transition indicates the successful
completion of a DTLS rehandshake.
WTP: This state transition occurs when the WTP receives the DTLS
Finished message from the AC, completing the DTLS re-handshake.
AC: This state transition occurs when the AC sends a DTLS Finished
message to the WTP, completing the DTLS re-handshake.
Rekey to Shutdown (Q) This state transition indicates the failure of
the DTLS rekey operation.
WTP: This state transition occurs when there is a failure in the
rehandshake negotiation with the AC.
AC: This state transition occurs when there is a failure in the
rehandshake negotiation with the WTP.
Shutdown to Idle (P) This state transition occurs upon transmission
of a DTLS Session termination message, or upon receipt of a DTLS
session termination message.
WTP: This state transition occurs after the WTP transmits the DTLS
session termination message. If the WTP receives a DTLS
session termination message, it sends the DTLSPeerDisconnect
notification to CAPWAP and moves to the Idle state.
AC: This state transition occurs after the AC transmits the DTLS
session termination message. If the AC receives a DTLS session
termination message, it sends the DTLSPeerDisconnect
notification to CAPWAP and moves to the Idle state.
2.4. Use of DTLS in the CAPWAP Protocol
DTLS is used as a tightly-integrated, secure wrapper for the CAPWAP
protocol. In this document DTLS and CAPWAP are discussed as
nominally distinct entitites; however they are very closely coupled,
and may even be implemented inseparably. Since there are DTLS
library implementations currently available, and since security
protocols (e.g. IPsec, TLS) are often implemented in widely
available acceleration hardware, it is both convenient and forward-
looking to maintain a modular distinction in this document.
This section describes a detailed walk-through of the interactions
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between the DTLS module and the CAPWAP module, via 'commands' (CAPWAP
to DTLS) and 'notifications' (DTLS to CAPWAP) as they would be
encountered during the normal course of operation.
2.4.1. DTLS Handshake Processing
Details of the DTLS handshake process are specified in [DTLS]. This
section describes the interactions between the DTLS session
establishment process and the CAPWAP protocol. In the normal case,
the DTLS handshake will proceed as follows (NOTE: this example uses
certificates, but preshared keys are also supported):
============ ============
WTP AC
============ ============
ClientHello ------>
<------ HelloVerifyRequest
(with cookie)
ClientHello ------>
(with cookie)
<------ ServerHello
<------ Certificate
<------ ServerHelloDone
(WTP callout for AC authorization)
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ------>
(AC callout for WTP
authorization)
[ChangeCipherSpec]
<------ Finished
DTLS, as specified, provides its own retransmit timers with an
exponential back-off. However, it will never terminate the handshake
due to non-responsiveness; rather, it will continue to increase its
back-off timer period. Hence, timing out incomplete DTLS handshakes
is entirely the responsiblity of the CAPWAP protocol.
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2.4.1.1. Join Operations
The WTP, either through the Discovery process, or through pre-
configuration, determines the AC to connect to. The WTP uses DTLS to
establish a secure connection to the selected AC. Prior to
initiation of the DTLS handshake, the WTP sets the WaitJoin timer.
Upon receipt of a ClientHello message containing a valid cookie, the
AC sets the WaitJoin timer. If the Join operation has not completed
prior to timer expiration, the Join process is aborted, the WTP
transitions back to Discovery state, and the AC transitions back to
Idle state. Upon successful completion of the Join process the
WaitJoin timer is deactivated.
2.4.2. DTLS Error Handling
If the AC does not respond to any DTLS messages sent by the WTP, the
DTLS specification calls for the WTP to retransmit these messages.
If the WaitJoin timer expires, CAPWAP will issue the DTLSAbort
command, causing DTLS to terminate the handshake and remove any
allocated session context. Note that DTLS MAY send a single TLS
Alert message to the AC to indicate session termination.
If the WTP does not respond to any DTLS messages sent by the AC, the
CAPWAP protocol allows for three possiblities, listed below. Note
that DTLS MAY send a single TLS Alert message to the AC to indicate
session termination.
o The message was lost in transit; in this case, the WTP will re-
transmit its last outstanding message, since it did not receive
the reply.
o The WTP sent a DTLS Alert, which was lost in transit; in this
case, the AC's WaitJoin timer will expire, and the session will be
terminated.
o Communication with the WTP has completely failed; in this case,
the AC's WaitJoin timer will expire, and the session will be
terminated.
The DTLS specification provides for retransmission of unacknowledged
requests. If retransmissions remain unacknowledged, the WaitJoin
timer will eventually expire, at which time the CAPWAP module will
terminate the session.
If a cookie fails to validate, this could represent a WTP error, or
it could represent a DoS attack. Hence, AC resource utilization
SHOULD be minimized. The AC MAY log a message indicating the
failure, but SHOULD NOT attempt to reply to the WTP.
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Since DTLS handshake messages are potentially larger than the maximum
record size, DTLS supports fragmenting of handshake messages across
multiple records. There are several potential causes of re-assembly
errors, including overlapping and/or lost fragments. The DTLS module
MUST send a DTLSReassemblyFailure notification to CAPWAP. Whether
precise information is given along with notification is an
implementation issue, and hence is beyond the scope of this document.
Upon receipt of such an error, the CAPWAP protocol implementation
SHOULD log an appropriate error message. Whether processing
continues or the DTLS session is terminated is implementation
dependent.
DTLS decapsulation errors consist of three types: decryption errors,
and authentication errors, and malformed DTLS record headers. Since
DTLS authenticates the data prior to encapsulation, if decryption
fails, it is difficult to detect this without first attempting to
authenticate the packet. If authentication fails, a decryption error
is also likely, but not guaranteed. Rather than attempt to derive
(and require the implementation of) algorithms for detecting
decryption failures, these are reported as authentication failures.
The DTLS module MUST provide a DTLSDecapFailure notification to
CAPWAP when such errors occur. If a malformed DTLS record header is
detected, the packets SHOULD be silently discarded, and the receiver
MAY log an error message.
There is currently only one encapsulation error defined: MTU
exceeeded. As part of DTLS session establishment, CAPWAP informs
DTLS of the MTU size. This may be dynamically modified at any time
when CAPWAP sends the DTLSMtuUpdate command to DTLS. DTLS returns
this notification to CAPWAP whenever a transmission request will
result in a packet which exceeds the MTU.
2.4.3. DTLS Rehandshake Behavior
DTLS rekeying (known in DTLS as "rehandshake") requires special
attention, as the DTLS specification provides no rehandshake
triggering mechanism. Rather, the application (in this case, CAPWAP)
is expected to manage this for itself. This section addressed
various aspects of rehandshake behavior.
One simple way to think of a DTLS session is as a pair of
unidirectional channels which are tightly bound together. A useful
analogy is the twisted pair used for phone wiring, with one line per
pair. Then, the rehandshake process can be thought of using the call
over the existing pair to establish a call over a new pair - that is,
an entirely new session is negotiated under the protection of the
existing session.
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This sounds simple enough, yet there is operational complexity in
changing over to the new session. In particular, how does each end
know when it is safe to delete the "old" session, and switch over to
the new one? If DTLS were not a datagram protocol, this would be
simpler, but the fact that message delivery is unreliable
significantly complicates things: when the AC (the "server")
transmits its Finished message, it cannot be sure that the WTP
received it until the WTP transmits data on the new channel.
This fact constrains the way in which we transition to the new
session, and delete the old one. The WTP, upon receipt of the AC's
Finished message for the new session, immediately makes the new
session active, and transmits no further data (e.g. echo requests,
statistics, etc) on the old channel, and sends a TLS "user_cancelled"
alert message on the old channel, after which the old session is
immediately deleted.
The AC, sets a DTLSSessionDelete timer, (see Section 4.5) and
immediately makes the new session active, and transmits no further
data (e.g. echo requests, statistics, etc) on the old channel.
If a TLS "user_cancelled" alert message is received on the old
channel, the session delete timer is deactivated, and the session is
deleted.
if the dtls-session-delete timer expires, a TLS "user_cancelled"
alert message is transmitted on the old channel, and the session is
deleted.
Note that there is a slight possibility that some packets may be in
flight when the session is deleted. However, since CAPWAP provides
reliable delivery, these packets will be retransmitted over the new
channel.
2.4.3.1. Peer Initiated Rehandshake Triggers
Since key lifetimes are not negotiable in DTLS, it is possible that a
rehandshake from a peer may occur at any time, and implementations
must be prepared for this eventuality. Presumably, communicating
devices will be within the same domain of control. This being the
case, overly-aggressive rekeying may be detected by simply monitoring
logs, assuming such activity is indeed logged. Hence,
implementations MUST log rekey attempts as they occur, reporting the
time and identifying information for the peer.
CAPWAP implementations MUST provide an administrative interface which
permits specification of key lifetimes in seconds. Also,
implementations which wait until this interval has expired to begin
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the rehandshake process are liable to encounter temporary service
lapses on heavily loaded networks, so implementations SHOULD begin
the rehandshake before the actual lifetime has elapsed.
Given the relatively low bandwidth we might reasonably expect over a
CAPWAP control channel and the strength of modern cryptographic
algorithms (e.g. AES-128, 3DES, etc), it is reasonable to assume
that lifetimes will typically be more than 8 hours. Given this
assumption, a good rule of thumb for deciding when to rekey is this:
deduct a random number of seconds from the lifetime (say, between 1%
and 5% of the lifetime), and begin the rehandshake process at that
point. Using a random value helps avert collisions, when both sides
initiate a rehandshake at the same time (discussed further below).
2.4.3.2. Time Based Rehandshake Triggers
CAPWAP implementations MUST provide an administrative interface which
permits specification of key lifetimes in seconds. Also,
implementations which wait until this interval has expired to begin
the rehandshake process are liable to encounter temporary service
lapses on heavily loaded networks, so implementations SHOULD begin
the rehandshake before the actual lifetime has elapsed.
Given the relatively low bandwidth we might reasonably expect over a
CAPWAP control channel and the strength of modern cryptographic
algorithms (e.g. AES-128, 3DES, etc), it is reasonable to assume
that key lifetimes will typically be more than 8 hours. Given this
assumption, a good rule of thumb for deciding when to rekey is this:
deduct a random number of seconds from the lifetime (say, between 1%
and 5% of the lifetime), and begin the rehandshake process at that
point. Using a random value helps avert collisions, when both sides
initiate a rehandshake at the same time.
2.4.3.3. Volume Based Rehandshake Triggers
CAPWAP implementations MUST provide an administrative interface which
permits specification of key lifetimes in packet count. Like time-
based, lifetimes, implementations which wait until this interval has
expired to begin the rehandshake process may encounter temporary
service lapses on heavily loaded networks, so implementations SHOULD
begin the rehandshake before the actual lifetime has elapsed.
Volume-based lifetime estimation for purposes of rehandshake
initiation is considerably more complex than time-based lifetime. In
addition to avoiding collisions, the maximum burst rate must be
known, and an extimate made, assuming rehandshake packets are lost,
etc. Hence, we do not specify a one-size-fits-all approach here, and
the specific algorithm used is implementation dependent.
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2.4.3.4. Rehandshake Collisions
A collision occurs when both sides initiate a rehandshake
simultaneously. No matter how much care is taken, rehandshake
collisions are a distinct possibility. Hence, a contention
resolution strategy is specified.
A rehandshake collision is detected when a system receives a
rehandshake initiation when it has one outstanding with the same
peer.
When this occurs, each side will compare its own address with that of
its peer (in network byte order).
The one with the lower of the two addresses will ignore the peer's
rehandshake message, and continue with its own rehandshake process.
The one with the higher message will immediately abort its current
rehandshake, and set the DTLSRehandshake timer (see Section 4.5); if
the peer with the lower address does not complete the rehandshake
before the timer expires, the peer with the higher address will re-
initiate.
2.4.4. DTLS EndPoint Authentication
DTLS supports endpoint authentication with certificates or preshared
keys. The TLS algorithm suites for each endpoint authentication
method are described below.
2.4.4.1. Authenticating with Certificates
Note that only block ciphers are currently recommended for use with
DTLS. To understand the reasoning behind this, see [26].
However,support for AES counter mode encryption is currently
progressing in the TLS working group, and once protocol identifiers
are available, they will be added below. At present, the following
algorithms MUST be supported when using certificates for CAPWAP
authentication:
o TLS_RSA_WITH_AES_128_CBC_SHA
o TLS_RSA_WITH_3DES_EDE_CBC_SHA
The following algorithms SHOULD be supported when using certificates:
o TLS_DH_RSA_WITH_AES_128_CBC_SHA
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o TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA
The following algorithms MAY be supported when using certificates:
o TLS_RSA_WITH_AES_256_CBC_SHA
o TLS_DH_RSA_WITH_AES_256_CBC_SHA
2.4.4.2. Authenticating with Preshared Keys
Pre-shared keys present significant challenges from a security
perspective, and for that reason, their use is strongly discouraged.
However, [13] defines 3 different methods for authenticating with
preshared keys:
o PSK key exchange algorithm - simplest method, ciphersuites use
only symmetric key algorithms
o DHE_PSK key exchange algorithm - use a PSK to authenticate a
Diffie-Hellman exchange. These ciphersuites give some additional
protection against dictionary attacks and also provide Perfect
Forward Secrecy (PFS).
o RSA_PSK key exchange algorithm - use RSA and certificates to
authenticate the server, in addition to using a PSK. This is not
susceptible to passive attacks.
The first approach (plain PSK) is susceptible to passive dictionary
attacks; hence, while this alorithm MAY be supported, special care
should be taken when choosing that method. In particular, user-
readable passphrases SHOULD NOT be used, and use of short PSKs should
be strongly discouraged. Additionally, DHE_PSK MUST be supported,
and RSA_PSK MAY be supported.
The following cryptographic algorithms MUST be supported when using
preshared keys:
o TLS_DHE_PSK_WITH_AES_128_CBC_SHA
o TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA
The following algorithms SHOULD be supported when using preshared
keys:
o TLS_DHE_PSK_WITH_AES_256_CBC_SHA
The following algorithms MAY be supported when using preshared keys:
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o TLS_PSK_WITH_AES_128_CBC_SHA
o TLS_PSK_WITH_AES_256_CBC_SHA
o TLS_PSK_WITH_3DES_EDE_CBC_SHA
o TLS_RSA_PSK_WITH_AES_128_CBC_SHA
o TLS_RSA_PSK_WITH_AES_256_CBC_SHA
o TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA
2.4.4.3. Certificate Usage
Validation of the certificates by the AC and WTP is required so that
only an AC may perform the functions of an AC and that only a WTP may
perform the functions of a WTP. This restriction of functions to the
AC or WTP requires that the certificates used by the AC MUST be
distinguishable from the certificate used by the WTP. To accomplish
this differentiation, the x.509v3 certificates MUST include the
Extensions field [11] and MUST include the NetscapeComment [15]
extension.
For an AC, the value of the NetscapeComment extension MUST be the
string "CAPWAP AC Device Certificate". For a WTP, the value of the
NetscapeComment extension MUST be the string "CAPWAP WTP Device
Certificate".
Part of the CAPWAP certificate validation process includes ensuring
that the proper string is included in the NetscapeComment extension,
and only allowing the CAPWAP session to be established if the
extension does not represent the same role as the device validating
the certificate. For instance, a WTP MUST NOT accept a certificate
whose NetscapeComment field is set to "CAPWAP WTP Device
Certificate".
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3. CAPWAP Transport
The CAPWAP protocol uses UDP as a transport, and can be used with
IPv4 or IPv6. This section details the specifics of how the CAPWAP
protocol works in conjunction with IP.
3.1. UDP Transport
Communication between a WTP and an AC is established according to the
standard UDP client/server model. One of the CAPWAP requirements is
to allow a WTP to reside behind a firewall and/or Network Address
Translation (NAT) device. Since the connection is initiated by the
WTP (client) to the well-known UDP port of the AC (server), the use
of UDP is a logical choice.
CAPWAP protocol control packets sent between the WTP and the AC use
well known UDP port [to be IANA assigned]. CAPWAP protocol data
packets sent between the WTP and the AC use UDP port [to be IANA
assigned].
3.2. AC Discovery
A WTP and an AC will frequently not reside in the same IP subnet
(broadcast domain). When this occurs, the WTP must be capable of
discovering the AC, without requiring that multicast services are
enabled in the network. This section describes how AC discovery is
performed by WTPs.
As the WTP attempts to establish communication with an AC, it sends
the Discovery Request message and receives the corresponding response
message from the AC(s). The WTP must send the Discovery Request
message to either the limited broadcast IP address (255.255.255.255),
a well known multicast address or to the unicast IP address of the
AC. Upon receipt of the Discovery Request message, the AC issues a
Discovery Response message to the unicast IP address of the WTP,
regardless of whether the Discovery Request message was sent as a
broadcast, multicast or unicast message.
WTP use of a limited IP broadcast, multicast or unicast IP address is
implementation dependent.
When a WTP transmits a Discovery Request message to a unicast
address, the WTP must first obtain the IP address of the AC. Any
static configuration of an AC's IP address on the WTP non-volatile
storage is implementation dependent. However, additional dynamic
schemes are possible, for example:
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DHCP: A comma delimited ASCII encoded list of AC IP addresses is
embedded in the DHCP vendor specific option 43 extension. An
example of the actual format of the vendor specific payload for
IPv4 is of the form "10.1.1.1, 10.1.1.2".
DNS: The DNS name "CAPWAP-AC-Address" MAY be resolvable to one or
more AC addresses.
3.3. Fragmentation/Reassembly
While fragmentation and reassembly services are provided by IP, the
CAPWAP protocol also provides such services. Environments where the
CAPWAP protocol is used involve firewall, Network Address Translation
(NAT) and "middle box" devices, which tend to drop IP fragments in
order to minimize possible Denial of Service attacks. By providing
fragmentation and reassembly at the application layer, any
fragmentation required due to the tunneling component of the CAPWAP
protocol becomes transparent to these intermediate devices.
Consequently, the CAPWAP protocol is not impacted by any network
configurations.
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4. CAPWAP Packet Formats
This section contains the CAPWAP protocol packet formats. A CAPWAP
protocol packet consists of a CAPWAP Transport Layer packet header
followed by a CAPWAP message. The CAPWAP message can be either of
type Control or Data, where Control packets carry signaling, and Data
packets carry user payloads. The CAPWAP frame formats for CAPWAP
Data packets, and for DTLS encapsulated CAPWAP Data and Control
packets. are as shown below:
CAPWAP Data Packet :
+--------------------------------+
| IP |UDP | CAPWAP | Wireless |
| Hdr |Hdr | Header | Payload |
+--------------------------------+
CAPWAP + Optional DTLS Data Packet Security:
+------------------------------------------------+
| IP |UDP | DTLS | CAPWAP | Wireless | DTLS |
| Hdr |Hdr | Hdr | Hdr | Payload | Trailer|
+------------------------------------------------+
\--authenticated-----------/
\--- encrypted-----------/
CAPWAP Control Packet (DTLS Security Required):
+-----------------------------------------------------------+
| IP |UDP | DTLS | CAPWAP | Control | Message | DTLS |
| Hdr |Hdr | Hdr | Header | Header | Element(s) | Trailer |
+-----------------------------------------------------------+
\-------authenticated-----------------/
\------------encrypted-------------------/
UDP: All CAPWAP packets are encapsulated within UDP. Section
Section 3.1 defines the specific UDP usage.
CAPWAP Header: All CAPWAP protocol packets use a common header that
immediately follows the UDP header. This header, is defined in
Section 4.1.
Wireless Payload: A CAPWAP protocol packet that contains a wireless
payload is known as a data frame. The CAPWAP protocol does not
dictate the format of the wireless payload, which is defined by
the appropriate wireless standard. Additional information is in
Section 4.2.
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Control Header: The CAPWAP protocol includes a signalling component,
known as the CAPWAP control protocol. All CAPWAP control packets
include a Control Header, which is defined in Section 4.3.1.
Message Elements: A CAPWAP Control packet includes one or more
message elements, which are found immediately following the
control header. These message elements are in a Type/Length/value
style header, defined in Section 4.4.
4.1. CAPWAP Transport Header
All CAPWAP protocol messages are encapsulated using a common header
format, regardless of the CAPWAP control or CAPWAP Data transport
used to carry the messages. However, certain flags are not
applicable for a given transport. Refer to the specific transport
section in order to determine which flags are valid.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| RID | HLEN |F|L|W|M| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fragment ID | Frag Offset |Rsv-2|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Radio MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) Wireless Specific Information |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version: A 4 bit field which contains the version of CAPWAP used in
this packet. The value for this draft is 0.
RID: A 5 bit field which contains the Radio ID number for this
packet. WTPs with multiple radios but a single MAC Address range
use this field to indicate which radio is associated with the
packet.
HLEN: Length of CAPWAP tunnel header in 4 byte words. (Similar to IP
header length). This length includes the optional headers.
F: The Fragment 'F' bit indicates whether this packet is a fragment.
When this bit is one (1), the packet is a fragment and MUST be
combined with the other corresponding fragments to reassemble the
complete information exchanged between the WTP and AC.
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L: The Not Last 'L' bit is valid only if the 'F' bit is set and
indicates whether the packet contains the last fragment of a
fragmented exchange between WTP and AC. When this bit is 1, the
packet is not the last fragment. When this bit is 0, the packet
is the last fragment.
W: The Wireless 'W' bit is used to specify whether the optional
wireless specific information field is present in the header. A
value of one (1) is used to represent the fact that the optional
header is present.
M: The M bit is used to indicate that the Radio MAC Address optional
header is present. This is used to communicate the MAC address of
the receiving radio when the native wireless packet. This field
MUST NOT be set to one in packets sent by the AC to the WTP.
Flags: A set of reserved bits for future flags in the CAPWAP header.
All implementations complying with version zero of this protocol
MUST set these bits to zero.
Fragment ID: An 16 bit field whose value is assigned to each group of
fragments making up a complete set. The fragment ID space is
managed individually for every WTP/AC pair. The value of Fragment
ID is incremented with each new set of fragments. The Fragment ID
wraps to zero after the maximum value has been used to identify a
set of fragments.
Fragment Offset: A 13 bit field that indicates where in the payload
will this fragment belong during re-assembly. This field is valid
when the 'F' bit is set to 1. The fragment offset is measured in
units of 8 octets (64 bits). The first fragment has offset zero.
Reserved: The 3-bit Reserved-2 field is reserved and set to 0 in this
version of the CAPWAP protocol.
Radio MAC Address: This optional field contains the MAC address of
the radio receiving the packet. This is useful in packets sent
from the WTP to the AC, when the native wireless frame format is
converted to 802.3 by the WTP. This field is only present if the
'M' bit is set.
The field contains the basic format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | MAC Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Length: The number of bytes in the MAC Address field. The length
field is present since new IEEE technologies are using 48 byte
MAC addresses.
MAC Address: The MAC Address of the receiving radio.
Wireless Specific Information: This optional field contains
technology specific information that may be used to carry per
packet wireless information. This field is only present if the
'W' bit is set.
The field contains the basic format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Wireless ID | Length | Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Wireless ID: The wireless binding identifier. The following
values are defined:
1 - : IEEE 802.11
Length: The length of the data field
Data: Wireless specific information, whose details are defined in
the technology specific binding section.
Payload: This field contains the header for a CAPWAP Data Message or
CAPWAP Control Message, followed by the data associated with that
message.
4.2. CAPWAP Data Messages
A CAPWAP protocol data message is a forwarded wireless frame. The
CAPWAP protocol defines two different modes of encapsulations; IEEE
802.3 and native wireless. IEEE 802.3 encapsulation requires that
the bridging function be performed in the WTP. An IEEE 802.3
encapsulated user payload frame has the following format:
+------------------------------------------------------+
| IP Header | UDP Header | CAPWAP Header | 802.3 Frame |
+------------------------------------------------------+
The CAPWAP protocol also defines the native wireless encapsulation
mode. The actual format of the encapsulated CAPWAP data frame is
subject to the rules defined under the specific wireless technology
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binding. As a consequence, each wireless technology binding MUST
define a section entitled "Payload encapsulation", which defines the
format of the wireless payload that is encapsulated within the CAPWAP
Data messages.
In the event that the encapsulated frame would exceed the transport
layer's MTU, the sender is responsible for the fragmentation of the
frame, as specified in Section 3.3.
4.3. CAPWAP Control Messages
The CAPWAP Control protocol provides a control channel between the
WTP and the AC. Control messages are divided into the following
distinct message types:
Discovery: CAPWAP Discovery messages are used to identify potential
ACs, their load and capabilities.
WTP Configuration: The WTP Configuration messages are used by the AC
to push a specific configuration to the WTP it has a control
channel with. Messages that deal with the retrieval of statistics
from the WTP also fall in this category.
Mobile Session Management: Mobile session management messages are
used by the AC to push specific mobile station policies to the
WTP.
Firmware Management: Messages in this category are used by the AC to
push a new firmware image to the WTP.
Discovery, WTP Configuration and Mobile Session Management messages
MUST be implemented. Firmware Management MAY be implemented.
In addition, technology specific bindings may introduce new control
channel commands.
4.3.1. Control Message Format
All CAPWAP control messages are sent encapsulated within the CAPWAP
header (see Section 4.1). Immediately following the CAPWAP header,
is the control header, which has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seq Num | Msg Element Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Stamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Msg Element [0..N] ...
+-+-+-+-+-+-+-+-+-+-+-+-+
4.3.1.1. Message Type
The Message Type field identifies the function of the CAPWAP control
message. The Message Type field is comprised of an IANA Enterprise
Number and a message type value field. The first two byte contain
the IANA Enterprise Number (for example, the IEEE 802.11 IANA
Enterprise number is 13277), and the second two bytes contain the
Message Type value. The message type field can be expressed as:
Message Type = IANA Enterprise Number * 256 + Message Type Value
The valid values for base CAPWAP Message Types are given in the table
below:
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CAPWAP Control Message Message Type
Value
Discovery Request 1
Discovery Response 2
Join Request 3
Join Response 4
Configuration Status 5
Configuration Status Response 6
Configuration Update Request 7
Configuration Update Response 8
WTP Event Request 9
WTP Event Response 10
Change State Event Request 11
Change State Event Response 12
Echo Request 13
Echo Response 14
Image Data Request 15
Image Data Response 16
Reset Request 17
Reset Response 18
Primary Discovery Request 19
Primary Discovery Response 20
Data Transfer Request 21
Data Transfer Response 22
Clear Config Indication 23
Mobile Config Request 24
Mobile Config Response 25
4.3.1.2. Sequence Number
The Sequence Number Field is an identifier value to match request and
response packet exchanges. When a CAPWAP packet with a request
message type is received, the value of the sequence number field is
copied into the corresponding response packet.
When a CAPWAP control message is sent, its internal sequence number
counter is monotonically incremented, ensuring that no two requests
pending have the same sequence number. This field will wrap back to
zero.
4.3.1.3. Message Element Length
The Length field indicates the number of bytes following the Sequence
Num field.
4.3.1.4. Flags
The Flags field MUST be set to zero.
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4.3.1.5. Time Stamp
The Timestamp contains the timestamp. PRC-TODO: Details need to be
added here, and I am waiting for info from Dave Perkins.
4.3.1.6. Message Element[0..N]
The message element(s) carry the information pertinent to each of the
control message types. Every control message in this specification
specifies which message elements are permitted.
4.3.2. Control Message Quality of Service
It is recommended that CAPWAP control messages be sent by both the AC
and the WTP with an appropriate Quality of Service precedence value,
ensuring that congestion in the network minimizes occurrences of
CAPWAP control channel disconnects. Therefore, a Quality of Service
enabled CAPWAP device should use the following values:
802.1P: The precedence value of 7 SHOULD be used.
DSCP: The DSCP tag value of 46 SHOULD be used.
4.4. CAPWAP Protocol Message Elements
This section defines the CAPWAP Protocol message elements which are
included in CAPWAP protocol control messages.
Message elements are used to carry information needed in control
messages. Every message element is identified by the Type field,
whose numbering space is managed via IANA (see Section 14). The
total length of the message elements is indicated in the Message
Element Length field.
All of the message element definitions in this document use a diagram
similar to the one below in order to depict its format. Note that in
order to simplify this specification, these diagrams do not include
the header fields (Type and Length). The header field values are
defined in the Message element descriptions.
Additional message elements may be defined in separate IETF
documents.
The format of a message element uses the TLV format shown here:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value ... |
+-+-+-+-+-+-+-+-+
Where Type (16 bit) identifies the character of the information
carried in the Value field and Length (16 bits) indicates the number
of bytes in the Value field.
4.4.1. AC Descriptor
The AC payload message element is used by the AC to communicate it's
current state. The value contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Hardware Version ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HW Ver | Software Version ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SW Ver | Stations | Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Limit | Active WTPs | Max WTPs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max WTPs | Security |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1 for AC Descriptor
Length: 18
Reserved: MUST be set to zero
Hardware Version: The AC's hardware version number
Software Version: The AC's Firmware version number
Stations: The number of mobile stations currently associated with
the AC
Limit: The maximum number of stations supported by the AC
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Active WTPs: The number of WTPs currently attached to the AC
Max WTPs: The maximum number of WTPs supported by the AC
Security: A 8 bit bit mask specifying the authentication credential
type supported by the AC. The following values are supported (see
Section 2.4.4):
1 - X.509 Certificate Based
2 - Pre-Shared Secret
4.4.2. AC IPv4 List
The AC List message element is used to configure a WTP with the
latest list of ACs in a cluster.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 2 for AC List
Length: 4
The AC IP Address: An array of 32-bit integers containing an AC's
IPv4 Address.
4.4.3. AC IPv6 List
The AC List message element is used to configure a WTP with the
latest list of ACs in a cluster.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC IP Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 3 for AC IPV6 List
Length: 16
The AC IP Address: An array of 32-bit integers containing an AC's
IPv6 Address.
4.4.4. AC Name
The AC name message element contains an ASCII representation of the
AC's identity. The value is a variable length byte string. The
string is NOT zero terminated.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Name ...
+-+-+-+-+-+-+-+-+
Type: 4 for AC Name
Length: > 0
Name: A variable length ASCII string containing the AC's name
4.4.5. AC Name with Index
The AC Name with Index message element is sent by the AC to the WTP
to configure preferred ACs. The number of instances where this
message element would be present is equal to the number of ACs
configured on the WTP.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index | AC Name...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 5 for AC Name with Index
Length: > 2
Index: The index of the preferred server (e.g., 1=primary,
2=secondary).
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AC Name: A variable length ASCII string containing the AC's name.
4.4.6. AC Timestamp
The AC Timestamp message element is sent by the AC to synchronize the
WTP's clock.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 6 for AC Timestamp
Length: 4
Timestamp: The AC's current time, allowing all of the WTPs to be
time synchronized in the format defined by Network Time Protocol
(NTP) in RFC 1305 [10].
4.4.7. Add MAC ACL Entry
The Add MAC Access Control List (ACL) Entry message element is used
by an AC to add a MAC ACL list entry on a WTP, ensuring that the WTP
no longer provides any service to the MAC addresses provided in the
message. The MAC Addresses provided in this message element are not
expected to be saved in non-volatile memory on the WTP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 7 for Add MAC ACL Entry
Length: >= 7
Num of Entries: The number of MAC Addresses in the array.
MAC Address: An array of MAC Addresses to add to the ACL.
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4.4.8. Add Mobile Station
The Add Mobile Station message element is used by the AC to inform a
WTP that it should forward traffic for a particular mobile station.
The Add Mobile Station message element will be accompanied by
technology specific binding information element which may include
security parameters. Consequently, the security parameters must be
applied by the WTP for the particular mobile.
Once a mobile station's policy has been pushed to the WTP through
this message element, an AC may change any policies by simply sending
a modified Add Mobile Station message element. When a WTP receives
an Add Mobile Station message element for an existing mobile station,
it must override any existing state it may have for the mobile
station in question. The latest Add Mobile Station message element
data overrides any previously received messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | VLAN Name...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 8 for Add Mobile
Length: >= 7
Radio ID: An 8-bit value representing the radio
MAC Address: The mobile station's MAC Address
VLAN Name: An optional variable string containing the VLAN Name on
which the WTP is to locally bridge user data. Note this field is
only valid with WTPs configured in Local MAC mode.
4.4.9. Add Static MAC ACL Entry
The Add Static MAC ACL Entry message element is used by an AC to add
a permanent ACL entry on a WTP, ensuring that the WTP no longer
provides any service to the MAC addresses provided in the message.
The MAC Addresses provided in this message element are expected to be
saved in non-volative memory on the WTP.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 9 for Add Static MAC ACL Entry
Length: >= 7
Num of Entries: The number of MAC Addresses in the array.
MAC Address: An array of MAC Addresses to add to the permanent ACL.
4.4.10. CAPWAP Timers
The CAPWAP Timers message element is used by an AC to configure
CAPWAP timers on a WTP.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discovery | Echo Request |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 10 for CAPWAP Timers
Length: 2
Discovery: The number of seconds between CAPWAP Discovery packets,
when the WTP is in the discovery mode.
Echo Request: The number of seconds between WTP Echo Request CAPWAP
messages.
4.4.11. Change State Event
The Change State message element is used to communicate a change in
the operational state of a radio. The value contains two fields, as
shown.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | State | Cause |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 11 for Change State Event
Length: 3
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
State: An 8-bit boolean value representing the state of the radio.
A value of one disables the radio, while a value of two enables
it.
Cause: In the event of a radio being inoperable, the cause field
would contain the reason the radio is out of service. The
following values are supported:
0 - Normal
1 - Radio Failure
2 - Software Failure
4.4.12. Data Transfer Data
The Data Transfer Data message element is used by the WTP to provide
information to the AC for debugging purposes.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Type | Data Length | Data ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 12 for Data Transfer Data
Length: >= 3
Data Type: An 8-bit value the type of information being sent. The
following values are supported:
1 - WTP Crash Data
2 - WTP Memory Dump
Data Length: Length of data field.
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Data: Debug information.
4.4.13. Data Transfer Mode
The Data Transfer Mode message element is used by the AC to request
information from the WTP for debugging purposes.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Data Type |
+-+-+-+-+-+-+-+-+
Type: 13 for Data Transfer Mode
Length: 1
Data Type: An 8-bit value the type of information being requested.
The following values are supported:
1 - WTP Crash Data
2 - WTP Memory Dump
4.4.14. Decryption Error Report
The Decryption Error Report message element value is used by the WTP
to inform the AC of decryption errors that have occurred since the
last report. Note that this error reporting mechanism is not used if
encryption and decryption services are provided via the AC.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID |Num Of Entries | Mobile MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 14 for Decryption Error Report
Length: >= 8
Radio ID: The Radio Identifier, which typically refers to an
interface index on the WTP
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Num Of Entries: An 8-bit unsigned integer indicating the number of
mobile MAC addresses.
Mobile MAC Address: An array of mobile station MAC addresses that
have caused decryption errors.
4.4.15. Decryption Error Report Period
The Decryption Error Report Period message element value is used by
the AC to inform the WTP how frequently it should send decryption
error report messages.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Report Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 15 for Decryption Error Report Period
Length: 3
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP
Report Interval: A 16-bit unsigned integer indicating the time, in
seconds
4.4.16. Delete MAC ACL Entry
The Delete MAC ACL Entry message element is used by an AC to delete a
MAC ACL entry on a WTP, ensuring that the WTP provides service to the
MAC addresses provided in the message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 16 for Delete MAC ACL Entry
Length: >= 7
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Num of Entries: The number of MAC Addresses in the array.
MAC Address: An array of MAC Addresses to delete from the ACL.
4.4.17. Delete Mobile Station
The Delete Mobile station message element is used by the AC to inform
an WTP that it should no longer provide service to a particular
mobile station. The WTP must terminate service immediately upon
receiving this message element.
The transmission of a Delete Mobile Station message element could
occur for various reasons, including for administrative reasons, as a
result of the fact that the mobile has roamed to another WTP, etc.
Once access has been terminated for a given station, any future
packets received from the mobile station must result in a
deauthenticate message, as specified in [6].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 17 for Delete Mobile Station
Length: 7
Radio ID: An 8-bit value representing the radio
MAC Address: The mobile station's MAC Address
4.4.18. Delete Static MAC ACL Entry
The Delete Static MAC ACL Entry message element is used by an AC to
delete a previously added static MAC ACL entry on a WTP, ensuring
that the WTP provides service to the MAC addresses provided in the
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num of Entries| MAC Address[] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address[] |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 18 for Delete Static MAC ACL Entry
Length: >= 7
Num of Entries: The number of MAC Addresses in the array.
MAC Address: An array of MAC Addresses to delete from the static MAC
ACL entry.
4.4.19. Discovery Type
The Discovery message element is used to configure a WTP to operate
in a specific mode.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Discovery Type|
+-+-+-+-+-+-+-+-+
Type: 19 for Discovery Type
Length: 1
Discovery Type: An 8-bit value indicating how the AC was discovered.
The following values are supported:
0 - Broadcast
1 - Configured
4.4.20. Duplicate IPv4 Address
The Duplicate IPv4 Address message element is used by a WTP to inform
an AC that it has detected another IP device using the same IP
address it is currently using.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 20 for Duplicate IPv4 Address
Length: 10
IP Address: The IP Address currently used by the WTP.
MAC Address: The MAC Address of the offending device.
4.4.21. Duplicate IPv6 Address
The Duplicate IPv6 Address message element is used by a WTP to inform
an AC that it has detected another host using the same IP address it
is currently using.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 21 for Duplicate IPv6 Address
Length: 22
IP Address: The IP Address currently used by the WTP.
MAC Address: The MAC Address of the offending device.
4.4.22. Idle Timeout
The Idle Timeout message element is sent by the AC to the WTP to
provide it with the idle timeout that it should enforce on its active
mobile station entries.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timeout |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 22 for Idle Timeout
Length: 4
Timeout: The current idle timeout to be enforced by the WTP.
4.4.23. Image Data
The image data message element is present in the Image Data Request
message sent by the AC and contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Checksum | Image Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Image Data ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 23 for Image Data
Length: >= 4 (allows 0 length element if last data unit is 1024
bytes)
Opcode: An 8-bit value representing the transfer opcode. The
following values are supported:
3 - Image data is included
5 - An error occurred. Transfer is aborted
Checksum: A 16-bit value containing a checksum of the image data
that follows
Image Data: The Image Data field contains 1024 characters, unless
the payload being sent is the last one (end of file). If the last
block was 1024 in length, an Image Data with a zero length payload
is sent.
4.4.24. Image Filename
The image filename message element is sent by the WTP to the AC and
is used to initiate the firmware download process. This message
element contains the image filename, which the AC subsequently
transfers to the WTP via the Image Data message element. The value
is a variable length byte string, which is NOT zero terminated.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Filename ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 24 for Image Filename
Length: >= 1
Filename: A variable length string containing the filename to
download.
4.4.25. Initiate Download
The Initiate Download message element is used by the AC to inform the
WTP that it should initiate a firmware upgrade. This is performed by
having the WTP initiate its own Image Data Request, with the Image
Download message element. This message element does not contain any
data.
Type: 25 for Initiate Download
Length: 0
4.4.26. Location Data
The Location Data message elementis a variable length byte string
containing user defined location information (e.g. "Next to
Fridge"). This information is configurable by the network
administrator, and allows for the WTP location to be determined
through this field. The string is not zero terminated.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-
| Location ...
+-+-+-+-+-+-+-+-+-
Type: 26 for Location Data
Length: > 0
Timeout: A non-zero terminated string containing the WTP location.
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4.4.27. MTU Discovery Padding
The MTU Discovery Padding message element is used as padding to
perform MTU discovery, and MUST contain octets of value 0xFF, of any
length
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Padding...
+-+-+-+-+-+-+-+-
Type: 27 for MTU Discovery Padding
Length: variable
Timeout: A variable length pad.
4.4.28. Radio Administrative State
The administrative event message element is used to communicate the
state of a particular radio. The value contains the following
fields.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Admin State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 28 for Administrative State
Length: 2
Radio ID: An 8-bit value representing the radio to configure. The
Radio ID field may also include the value of 0xff, which is used
to identify the WTP itself. Therefore, if an AC wishes to change
the administrative state of a WTP, it would include 0xff in the
Radio ID field.
Admin State: An 8-bit value representing the administrative state of
the radio. The following values are supported:
1 - Enabled
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2 - Disabled
4.4.29. Result Code
The Result Code message element value is a 32-bit integer value,
indicating the result of the request operation corresponding to the
sequence number in the message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 29 for Result Code
Length: 4
Result Code: The following values are defined:
0 Success
1 Failure (AC List message element MUST be present)
2 Success (NAT detected)
3 Failure (unspecified)
4 Failure (Join Failure, Resource Depletion)
5 Failure (Join Failure, Unknown Source)
6 Failure (Join Failure, Incorrect Data)
7 Failure (Join Failure, Session ID already in use)
4.4.30. Session ID
The session ID message element value contains a randomly generated
unsigned 32-bit integer.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 30 for Session ID
Length: 4
Session ID: A 32-bit random session identifier
4.4.31. Statistics Timer
The statistics timer message element value is used by the AC to
inform the WTP of the frequency which it expects to receive updated
statistics.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Statistics Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 31 for Statistics Timer
Length: 2
Statistics Timer: A 16-bit unsigned integer indicating the time, in
seconds
4.4.32. Vendor Specific Payload
The Vendor Specific Payload is used to communicate vendor specific
information between the WTP and the AC. The value contains the
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Element ID | Value... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 32 for Vendor Specific
Length: >= 7
Vendor Identifier: A 32-bit value containing the IANA assigned "SMI
Network Management Private Enterprise Codes" [19]
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Element ID: A 16-bit Element Identifier which is managed by the
vendor.
Value: The value associated with the vendor specific element.
4.4.33. WTP Board Data
The WTP Board Data message element is sent by the WTP to the AC and
contains information about the hardware present.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional additional vendor specific WTP board data TLVs
Type: 33 for WTP Board Data
Length: >=14
Vendor Identifier: A 32-bit value containing the IANA assigned "SMI
Network Management Private Enterprise Codes"
Type: The following values are supported:
0 - WTP Model Number: The WTP Model Number MUST be included in
the WTP Board Data message element.
1 - WTP Serial Number: The WTP Serial Number MUST be included in
the WTP Board Data message element.
2 - Board ID: A hardware identifier, which MAY be included in the
WTP Board Data mesage element.
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3 - Board Revision A revision number of the board, which MAY be
included in the WTP Board Data message element.
4.4.34. WTP Descriptor
The WTP descriptor message element is used by a WTP to communicate
it's current hardware/firmware configuration. The value contains the
following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Radios | Radios in use | Encryption Capabilities |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 34 for WTP Descriptor
Length: >= 31
Max Radios: An 8-bit value representing the number of radios (where
each radio is identified via the RID field) supported by the WTP
Radios in use: An 8-bit value representing the number of radios
present in the WTP
Encryption Capabilities: This 16-bit field is used by the WTP to
communicate it's capabilities to the AC. Since most WTP's support
link layer encryption, the AC may make use of these services.
There are binding dependent encryption capabilities. A WTP that
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does not have any encryption capabilities would set this field to
zero (0). Refer to the specific binding for further specification
of the Encryption Capabilities field.
Vendor Identifier: A 32-bit value containing the IANA assigned "SMI
Network Management Private Enterprise Codes"
Type: The following values are supported. The Hardware Version,
Software Version, and Boot Version values MUST be included.
0 - WTP Model Number: The WTP Model Number MUST be included in
the WTP Board Data message element.
1 - WTP Serial Number: The WTP Serial Number MUST be included in
the WTP Board Data message element.
2 - Board ID: A hardware identifier, which MAY be included in the
WTP Board Data mesage element.
3 - Board Revision A revision number of the board, which MAY be
included in the WTP Board Data message element.
4 - Hardware Version: A 32-bit integer representing the WTP's
hardware version number
5 - Software Version: A 32-bit integer representing the WTP's
Firmware version number
6 - Boot Version: A 32-bit integer representing the WTP's boot
loader's version number
4.4.35. WTP Fallback
The WTP Fallback message element is sent by the AC to the WTP to
enable or disable automatic CAPWAP fallback in the event that a WTP
detects its preferred AC, and is not currently connected to it.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Mode |
+-+-+-+-+-+-+-+-+
Type: 35 for WTP Fallback
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Length: 1
Mode: The 8-bit value indicates the status of automatic CAPWAP
fallback on the WTP. A value of zero disables fallback, while a
value of one enables it. When enabled, if the WTP detects that
its primary AC is available, and it is not connected to it, it
SHOULD automatically disconnect from its current AC and reconnect
to its primary. If disabled, the WTP will only reconnect to its
primary through manual intervention (e.g., through the Reset
Request command).
4.4.36. WTP Frame Encapsulation Type
The WTP Frame EncapsultationType message element allows the WTP to
communicate the encapsulation type, or tunneling modes of operation
which it supports to the AC. A WTP that advertises support for all
types allows the AC to select which type will be used, based on its
local policy.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Frame Enc Type |
+-+-+-+-+-+-+-+-+
Type: 36 for WTP Frame Encapsulation Type
Length: 1
Frame Encapsulation Type: The Frame type specifies the encapsulation
modes supported by the WTP. The following values are supported:
1 - Local Bridging: Local Bridging allows the WTP to perform the
bridging function. This value MUST NOT be used when the WTP
MAC Type is set to Split-MAC.
2 - 802.3 Bridging: 802.3 Bridging requires the WTP and AC to
encapsulate all user payload as native IEEE 802.3 frames (see
Section 4.2). This value MUST NOT be used when the WTP MAC
Type is set to Split-MAC.
4 - Native Bridging: Native Bridging requires the WTP and AC to
encapsulate all user payloads as native wireless frames, as
defined by the wireless binding (see Section 4.2).
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7 - All: The WTP is capable of supporting all frame encapsulation
types.
4.4.37. WTP IPv4 IP Address
The WTP IPv4 address is used to perform NAT detection.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP IPv4 IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 37 for WTP IPv4 IP Address
Length: 4
WTP IPv4 IP Address: The IPv4 address from which the WTP is sending
packets. This field is used for NAT detection.
4.4.38. WTP MAC Type
The WTP MAC-Type message element allows the WTP to communicate its
mode of operation to the AC. A WTP that advertises support for both
modes allows the AC to select the mode to use, based on local policy.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MAC Type |
+-+-+-+-+-+-+-+-+
Type: 38 for WTP MAC Type
Length: 1
MAC Type: The MAC mode of operation supported by the WTP. The
following values are supported
0 - Local-MAC: Local-MAC is the default mode that MUST be
supported by all WTPs.
1 - Split-MAC: Split-MAC support is optional, and allows the AC
to receive and process native wireless frames.
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2 - Both: WTP is capable of supporting both Local-MAC and Split-
MAC.
4.4.39. WTP Radio Information
The WTP radios information message element is used to communicate the
radio information in a specific slot. The Discovery Request MUST
include one such message element per radio in the WTP. The Radio-
Type field is used by the AC in order to determine which technology
specific binding is to be used with the WTP.
The value contains two fields, as shown.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Radio Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio Type |
+-+-+-+-+-+-+-+-+
Type: 39 for WTP Radio Information
Length: 5
Radio ID: The Radio Identifier, which typically refers to an
interface index on the WTP
Radio Type: The type of radio present. Note this bitfield can be
used to specify support for more than a single type of PHY/MAC.
The following values are supported:
1 - 802.11b: An IEEE 802.11b radio.
2 - 802.11a: An IEEE 802.11a radio.
4 - 802.11g: An IEEE 802.11g radio.
8 - 802.11n: An IEEE 802.11n radio.
0xOF - 802.11b, 802.11a, 802.11g and 802.11n: The 4 radio types
indicated are supported in the WTP.
4.4.40. WTP Manager Control IPv4 Address
The WTP Manager Control IPv4 Address message element is sent by the
AC to the WTP during the discovery process and is used by the AC to
provide the interfaces available on the AC, and the current number of
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WTPs connected. In the event that multiple WTP Manager Control IPV4
Address message elements are returned, the WTP is expected to perform
load balancing across the multiple interfaces.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 40 for WTP Manager Control IPv4 Address
Length: 6
IP Address: The IP Address of an interface.
WTP Count: The number of WTPs currently connected to the interface.
4.4.41. WTP Manager Control IPv6 Address
The WTP Manager Control IPv6 Address message element is sent by the
AC to the WTP during the discovery process and is used by the AC to
provide the interfaces available on the AC, and the current number of
WTPs connected. This message element is useful for the WTP to
perform load balancing across multiple interfaces.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 41 for WTP Manager Control IPv6 Address
Length: 18
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IP Address: The IP Address of an interface.
WTP Count: The number of WTPs currently connected to the interface.
4.4.42. WTP Name
The WTP Name message element is a variable length bye string. The
string is not zero terminated.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-
| WTP Name ...
+-+-+-+-+-+-+-+-+-
Type: 42 for WTP Name
Length: variable
WTP Name: A non-zero terminated string containing the WTP name.
4.4.43. WTP Reboot Statistics
The WTP Reboot Statistics message element is sent by the WTP to the
AC to communicate reasons why reboots have occurred.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Crash Count | CAPWAP Initiated Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Failure Count | Failure Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 43 for WTP Reboot Statistics
Length: 7
Crash Count: The number of reboots that have occurred due to a WTP
crash. A value of 65535 implies that this information is not
available on the WTP.
CAPWAP Initiated Count: The number of reboots that have occurred at
the request of a CAPWAP protocol message, such as a change in
configuration that required a reboot or an explicit CAPWAP reset
request. A value of 65535 implies that this information is not
available on the WTP.
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Link Failure Count: The number of times that a CAPWAP protocol
connection with an AC has failed.
Failure Type: The last WTP failure. The following values are
supported:
0 - Link Failure
1 - CAPWAP Initiated (see Section 9.3)
2 - WTP Crash
255 - Unknown (e.g., WTP doesn't keep track of info)
4.4.44. WTP Static IP Address Information
The WTP Static IP Address Information message element is used by an
AC to configure or clear a previously configured static IP address on
a WTP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netmask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gateway |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Static |
+-+-+-+-+-+-+-+-+
Type: 44 for WTP Static IP Address Information
Length: 13
IP Address: The IP Address to assign to the WTP. This field is only
valid if the static field is set to one.
Netmask: The IP Netmask. This field is only valid if the static
field is set to one.
Gateway: The IP address of the gateway. This field is only valid if
the static field is set to one.
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Netmask: The IP Netmask. This field is only valid if the static
field is set to one.
Static: An 8-bit boolean stating whether the WTP should use a static
IP address or not. A value of zero disables the static IP
address, while a value of one enables it.
4.5. CAPWAP Protocol Timers
A WTP or AC that implements CAPWAP discovery MUST implement the
following timers.
4.5.1. DiscoveryInterval
The minimum time, in seconds, that a WTP MUST wait after receiving a
Discovery Response, before initiating a DTLS handshake.
Default: 5
4.5.2. DTLSRehandshake
The minimum time, in seconds, a WTP MUST wait for DTLS rehandshake to
complete.
Default: 10
4.5.3. DTLSSessionDelete
The minimum time, in seconds, a WTP MUST wait for DTLS session
deletion.
Default: 5
4.5.4. EchoInterval
The minimum time, in seconds, between sending echo requests to the AC
with which the WTP has joined.
Default: 30
4.5.5. KeyLifetime
The maximum time, in seconds, which a CAPWAP DTLS session key is
valid.
Default: 28800
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4.5.6. MaxDiscoveryInterval
The maximum time allowed between sending discovery requests from the
interface, in seconds. Must be no less than 2 seconds and no greater
than 180 seconds.
Default: 20 seconds.
4.5.7. NeighborDeadInterval
The minimum time, in seconds, a WTP MUST wait without having received
Echo Responses to its Echo Requests, before the destination for the
Echo Request may be considered dead. Must be no less than
2*EchoInterval seconds and no greater than 240 seconds.
Default: 60
4.5.8. ResponseTimeout
The minimum time, in seconds, which the WTP or AC must respond to a
CAPWAP Request message.
Default: 1
4.5.9. RetransmitInterval
The minimum time, in seconds, which a non-acknowledged CAPWAP packet
will be retransmitted.
Default: 3
4.5.10. SilentInterval
The minimum time, in seconds, a WTP MUST wait after failing to
receive any responses to its discovery requests, before it MAY again
send discovery requests.
Default: 30
4.5.11. WaitJoin
The maximum time, in seconds, a WTP MUST wait without having received
a DTLS Handshake message from an AC. This timer must be greater than
30 seconds.
Default: 60
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4.6. CAPWAP Protocol Variables
A WTP or AC that implements CAPWAP discovery MUST allow for the
following variables to be configured by system management; default
values are specified so as to make it unnecessary to configure any of
these variables in many cases.
4.6.1. DiscoveryCount
The number of discoveries transmitted by a WTP to a single AC. This
is a monotonically increasing counter.
4.6.2. MaxDiscoveries
The maximum number of discovery requests that will be sent after a
WTP boots.
Default: 10
4.6.3. MaxRetransmit
The maximum number of retransmissions for a given CAPWAP packet
before the link layer considers the peer dead.
Default: 5
4.6.4. RetransmitCount
The number of retransmissions for a given CAPWAP packet. This is a
monotonically increasing counter.
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5. CAPWAP Discovery Operations
The Discovery messages are used by a WTP to determine which ACs are
available to provide service, and the capabilities and load of the
ACs.
5.1. Discovery Request Message
The Discovery Request message is used by the WTP to automatically
discover potential ACs available in the network. The Discovery
Request message provides ACs with the primary capabilities of the
WTP. A WTP must exchange this information to ensure subsequent
exchanges with the ACs are consistent with the WTP's functional
characteristics. A WTP must transmit this command even if it has a
statically configured AC.
Discovery Request messages MUST be sent by a WTP in the Discover
state after waiting for a random delay less than
MaxDiscoveryInterval, after a WTP first comes up or is
(re)initialized. A WTP MUST send no more than the maximum of
MaxDiscoveries Discovery Request messages, waiting for a random delay
less than MaxDiscoveryInterval between each successive message.
This is to prevent an explosion of WTP Discovery Request messages.
An example of this occurring is when many WTPs are powered on at the
same time.
Discovery Request messages MUST be sent by a WTP when no Echo
Response messages are received for NeighborDeadInterval and the WTP
returns to the Idle state. Discovery Request messages are sent after
NeighborDeadInterval. They MUST be sent after waiting for a random
delay less than MaxDiscoveryInterval. A WTP MAY send up to a maximum
of MaxDiscoveries Discovery Request messages, waiting for a random
delay less than MaxDiscoveryInterval between each successive message.
If a Discovery Response message is not received after sending the
maximum number of Discovery Request messages, the WTP enters the
Sulking state and MUST wait for an interval equal to SilentInterval
before sending further Discovery Request messages.
The Discovery Request message may be sent as a unicast, broadcast or
multicast message.
Upon receiving a Discovery Request message, the AC will respond with
a Discovery Response message sent to the address in the source
address of the received discovery request message.
The following message elements MUST be included in the Discovery
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Request message:
o Discovery Type, see Section 4.4.19
o WTP Descriptor, see Section 4.4.34
o WTP Frame Type, see Section 4.4.36
o WTP MAC Type, see Section 4.4.38
o WTP Radio Information, see Section 4.4.39
5.2. Discovery Response Message
The Discovery Response message provides a mechanism for an AC to
advertise its services to requesting WTPs.
The Discovery Response message is sent by an AC after receiving a
Discovery Request message from a WTP.
When a WTP receives a Discovery Response message, it MUST wait for an
interval not less than DiscoveryInterval for receipt of additional
Discovery Response messages. After the DiscoveryInterval elapses,
the WTP enters the DTLS-Init state and selects one of the ACs that
sent a Discovery Response message and send a DTLS Handshake to that
AC.
The following message elements MUST be included in the Discovery
Response Message:
o AC Descriptor, see Section 4.4.1
o AC Name, see Section 4.4.4
o WTP Manager Control IPv4 Address, see Section 4.4.40
o WTP Manager Control IPv6 Address, see Section 4.4.41
5.3. Primary Discovery Request Message
The Primary Discovery Request message is sent by the WTP to determine
whether its preferred (or primary) AC is available.
A Primary Discovery Request message is sent by a WTP when it has a
primary AC configured, and is connected to another AC. This
generally occurs as a result of a failover, and is used by the WTP as
a means to discover when its primary AC becomes available. As a
consequence, this message is only sent by a WTP when it is in the Run
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state.
The frequency of the Primary Discovery Request messages should be no
more often than the sending of the Echo Request message.
Upon receipt of a Discovery Request message, the AC responds with a
Primary Discovery Response message sent to the address in the source
address of the received Primary Discovery Request message.
The following message elements MUST be included in the Primary
Discovery Request message.
o Discovery Type, see Section 4.4.19
o WTP Descriptor, see Section 4.4.34
o WTP Frame Type, see Section 4.4.36
o WTP MAC Type, see Section 4.4.38
o WTP Radio Information, see Section 4.4.39 A WTP Radio Information
message element MUST be present for every radio in the WTP.
5.4. Primary Discovery Response
The Primary Discovery Response message enables an AC to advertise its
availability and services to requesting WTPs that are configured to
have the AC as its primary AC.
The Primary Discovery Response message is sent by an AC after
receiving a Primary Discovery Request message.
When a WTP receives a Primary Discovery Response message, it may
establish a CAPWAP protocol connection to its primary AC, based on
the configuration of the WTP Fallback Status message element on the
WTP.
The following message elements MUST be included in the Primary
Discovery Response message.
o AC Descriptor, see Section 4.4.1
o AC Name, see Section 4.4.4
o WTP Manager Control IPv4 Address, see Section 4.4.40
o WTP Manager Control IPv6 Address, see Section 4.4.41
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6. CAPWAP Join Operations
The Join Request message is used by a WTP to request service from an
AC after a DTLS connection is established to that AC. The Join
Response message is used by the the AC to indicate that it will or
will not provide service.
6.1. Join Request
The Join Request message is used by a WTP to inform an AC that it
wishes to provide services through the AC. A Join Request message is
sent by a WTP after receiving one or more Discovery Responses, and
completion of DTLS session establishment. When an AC receives a Join
Request message it responds with a Join Response message.
Upon completion of the DTLS handshake (synonymous with DTLS "session
establishment"), the WTP sends the Join Request message to the AC.
Upon receipt of the Join Request Message, the AC generates a Join
Response message and sends it to the WTP, indicating success or
failure.
Upon transmission of the Join Request message, the WTP sets the
WaitJoin timer. If the Join Response message has not been received
prior to expiration, the WTP aborts the Join process and transitions
back to the Discovery state, see Section 2.3.1). Upon receipt of the
Join Response message, the WaitJoin timer is deactivated.
If the AC rejects the Join Request, it sends a Join Response with a
failure indication then enters the CAPWAP reset state, resulting in
shutdown of the DTLS session.
Upon determining which AC to join, the WTP creates session state
containing the AC address and session ID, creates the Join Request
message, sets the WaitJoin timer for the session and sends the Join
Request message to the AC.
If an invalid (i.e. malformed) Join Request message is received, the
message MUST be silently discarded by the AC. No response is sent to
the WTP. The AC SHOULD log this event.
The following message elements MUST be included in the Join Request
message.
o Location Data, see Section 4.4.26
o Session ID, see Section 4.4.30
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o WTP Descriptor, see Section 4.4.34
o WTP IPv4 IP Address, see Section 4.4.37
o WTP Name, see Section 4.4.42
o WTP Radio Information, see Section 4.4.39 A WTP Radio Information
message element MUST be present for every radio in the WTP.
6.2. Join Response
The Join Response message is sent by the AC to indicate to a WTP that
it is capable and willing to provide service to it.
After determining that a WTP should join the AC, the AC creates
session state containing the WTP address, port and session ID, sets
the WaitJoin timer for the session, sends the Join Response message
to the WTP.
The WTP, receiving a Join Response message checks for success or
failure. If the message indicates success, the WTP clears the
WaitJoin timer for the session and proceeds to the Configure or Image
Data state. Otherwise, the WTP enters the CAPWAP reset state,
resulting in shutdown of the DTLS session.
If the WaitJoin Timer expires prior to reception of the Join Response
message, the WTP MUST terminate the handshake, deallocate associated
session state and transition to the Discover state.
If an invalid (malformed) Join Response message is received, the WTP
SHOULD log an informative message detailing the error. This error
MUST be treated in the same manner as AC non-responsiveness. In this
way, the WaitJoin timer will eventually expire, in which case the WTP
may (if it is so configured) attempt to join with an alternative AC.
The following message elements MAY be included in the Join Response
message.
o Result Code, see Section 4.4.29
o AC IPv4 List, see Section 4.4.2
o AC IPv6 List, see Section 4.4.3
o Session ID, see Section 4.4.30
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7. Control Channel Management
The Control Channel Management messages are used by the WTP and AC to
maintain a control communication channel.
7.1. Echo Request
The Echo Request message is a keep alive mechanism for CAPWAP control
messages.
Echo Request messages are sent periodically by a WTP in the Run state
(see Section 2.3) to determine the state of the connection between
the WTP and the AC. The Echo Request message is sent by the WTP when
the Heartbeat timer expires. The WTP MUST start its
NeighborDeadInterval timer when the Heartbeat timer expires.
The Echo Request message carries no message elements.
When an AC receives an Echo Request message it responds with an Echo
Response message.
7.2. Echo Response
The Echo Response message acknowledges the Echo Request message, and
is only processed while in the Run state (see Section 2.3).
An Echo Response message is sent by an AC after receiving an Echo
Request message. After transmitting the Echo Response message, the
AC SHOULD reset its Heartbeat timer to expire in the value configured
for EchoInterval. If another Echo Request message or other control
message is not received by the AC when the timer expires, the AC
SHOULD consider the WTP to be no longer be reachable.
The Echo Response message carries no message elements.
When a WTP receives an Echo Response message it stops the
NeighborDeadInterval timer, and initializes the Heartbeat timer to
the EchoInterval.
If the NeighborDeadInterval timer expires prior to receiving an Echo
Response message, or other control message, the WTP enters the Idle
state.
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8. WTP Configuration Management
Wireless Termination Point Configuration messages are used to
exchange configuration information between the AC and the WTP.
8.1. Configuration Consistency
The CAPWAP protocol provides flexibility in how WTP configuration is
managed. A WTP has two options:
1. The WTP retains no configuration and accepts the configuration
provided by the AC.
2. The WTP retains the configuration of parameters provided by the AC
that are non-default values.
If the WTP opts to save configuration locally, the CAPWAP protocol
state machine defines the Configure state, which allows for
configuration exchange. In the Configure state, the WTP sends its
current configuration overrides to the AC via the Configuration
Status message. A configuration override is a parameter that is non-
default. One example is that in the CAPWAP protocol, the default
antenna configuration is internal omni antenna. A WTP that either
has no internal antennas, or has been explicitly configured by the AC
to use external antennas, sends its antenna configuration during the
configure phase, allowing the AC to become aware of the WTP's current
configuration.
Once the WTP has provided its configuration to the AC, the AC sends
its own configuration. This allows the WTP to inherit the
configuration and policies from the AC.
An AC maintains a copy of each active WTP's configuration. There is
no need for versioning or other means to identify configuration
changes. If a WTP becomes inactive, the AC MAY delete the
configuration associated with it. If a WTP fails, and connects to a
new AC, it provides its overridden configuration parameters, allowing
the new AC to be aware of the WTP's configuration.
This model allows for resiliency in case of an AC failure, that
another AC can provide service to the WTP. In this scenario, the new
AC would be automatically updated with WTP configuration changes,
eliminating the need for inter-AC communication or the need for all
ACs to be aware of the configuration of all WTPs in the network.
Once the CAPWAP protocol enters the Run state, the WTPs begin to
provide service. It is quite common for administrators to require
that configuration changes be made while the network is operational.
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Therefore, the Configuration Update Request is sent by the AC to the
WTP to make these changes at run-time.
8.1.1. Configuration Flexibility
The CAPWAP protocol provides the flexibility to configure and manage
WTPs of varying design and functional characteristics. When a WTP
first discovers an AC, it provides primary functional information
relating to its type of MAC and to the nature of frames to be
exchanged. The AC configures the WTP appropriately. The AC also
establishes corresponding internal operations to deal with the WTP
according to its functionalities.
8.2. Configuration Status
The Configuration Status message is sent by a WTP to deliver its
current configuration to its AC.
Configuration Status messages are sent by a WTP while in the
Configure state.
The Configuration Status message carries binding specific message
elements. Refer to the appropriate binding for the definition of
this structure.
When an AC receives a Configuration Status message it will act upon
the content of the packet and respond to the WTP with a Configuration
Status Response message.
The Configuration Status message includes multiple Administrative
State message Elements. There is one such message element for the
WTP, and one message element per radio in the WTP.
The following message elements MUST be included in the Configuration
Status message.
o AC Name, see Section 4.4.4
o AC Name with Index, see Section 4.4.5
o Radio Administrative State, see Section 4.4.28
o Statistics Timer, see Section 4.4.31
o WTP Board Data, see Section 4.4.33
o WTP Static IP Address Information, see Section 4.4.44
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o WTP Reboot Statistics, see Section 4.4.43
8.3. Configuration Status Response
The Configuration Status Response message is sent by an AC and
provides a mechanism for the AC to override a WTP's requested
configuration.
Configuration Status Response messages are sent by an AC after
receiving a Configure Request message.
The Configuration Status Response message carries binding specific
message elements. Refer to the appropriate binding for the
definition of this structure.
When a WTP receives a Configuration Status Response message it acts
upon the content of the message, as appropriate. If the
Configuration Status Response message includes a Change State Event
message element that causes a change in the operational state of one
of the Radio, the WTP will transmit a Change State Event to the AC,
as an acknowledgement of the change in state.
The following message elements MUST be included in the Configuration
Status Response message.
o AC IPv4 List, see Section 4.4.2
o AC IPv6 List, see Section 4.4.3
o CAPWAP Timers, see Section 4.4.10
o Change State Event, see Section 4.4.11
o Decryption Error Report Period, see Section 4.4.15
o Idle Timeout, see Section 4.4.22
o WTP Fallback, see Section 4.4.35
8.4. Configuration Update Request
Configure Update Request messages are sent by the AC to provision the
WTP while in the Run state. This is used to modify the configuration
of the WTP while it is operational.
When an AC receives a Configuration Update Request message it will
respond with a Configuration Update Response message, with the
appropriate Result Code.
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One or more of the following message elements MAY be included in the
Configuration Update message.
o AC IPv4 List, see Section 4.4.2
o AC IPv6 List, see Section 4.4.3
o AC Name with Index, see Section 4.4.5
o AC Timestamp, see Section 4.4.6
o Add MAC ACL Entry, see Section 4.4.7
o Add Static MAC ACL Entry, see Section 4.4.9
o CAPWAP Timers, see Section 4.4.10
o Change State Event, see Section 4.4.11
o Decryption Error Report Period, see Section 4.4.15
o Delete MAC ACL Entry, see Section 4.4.16
o Delete Static MAC ACL Entry, see Section 4.4.18
o Idle Timeout, see Section 4.4.22
o Location Data, see Section 4.4.26
o Radio Administrative State, see Section 4.4.28
o Statistics Timer, see Section 4.4.31
o WTP Fallback, see Section 4.4.35
o WTP Name, see Section 4.4.42
8.5. Configuration Update Response
The Configuration Update Response message is the acknowledgement
message for the Configuration Update Request message.
The Configuration Update Response message is sent by a WTP after
receiving a Configuration Update Request message.
When an AC receives a Configure Update Response message the result
code indicates if the WTP successfully accepted the configuration.
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The following message element MUST be present in the Configuration
Update message.
Result Code, see Section 4.4.29
The following message elements MAY be present in the Configuration
Update message.
o AC IPv4 List, see Section 4.4.2
o AC IPv6 List, see Section 4.4.3
8.6. Change State Event Request
The Change State Event Request message is used by the WTP to inform
the AC of a change in the operational state.
The Change State Event Request message is sent by the WTP when it
receives a Configuration Response message that includes a Change
State Event message element. It is also sent when the WTP detects an
operational failure with a radio. The Change State Event Request
message may be sent in either the Configure or Run state (see
Section 2.3.
When an AC receives a Change State Event message it will respond with
a Change State Event Response message and make any necessary
modifications to internal WTP data structures.
The following message elements MUST be present in the Change State
Event Request message.
o Change State Event message element, see Section 4.4.11
8.7. Change State Event Response
The Change State Event Response message acknowledges the Change State
Event Request message.
A Change State Event Response message is by a WTP after receiving a
Change State Event Request message.
The Change State Event Response message carries no message elements.
Its purpose is to acknowledge the receipt of the Change State Event
Request message.
The WTP does not need to perform any special processing of the Change
State Event Response message.
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8.8. Clear Config Indication
The Clear Config Indication message is used to reset a WTP's
configuration.
The Clear Config Indication message is sent by an AC to request that
a WTP reset its configuration to the manufacturing default
configuration. The Clear Config Indication message is sent while in
the Run CAPWAP state.
The Clear Config Indication message carries no message elements.
When a WTP receives a Clear Config Indication message it resets its
configuration to the manufacturing default configuration.
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9. Device Management Operations
This section defines CAPWAP operations responsible for debugging,
gathering statistics, logging, and firmware management.
9.1. Image Data Request
The Image Data Request message is used to update firmware on the WTP.
This message and its companion response message are used by the AC to
ensure that the image being run on each WTP is appropriate.
Image Data Request messages are exchanged between the WTP and the AC
to download a new firmware image to the WTP. When a WTP or AC
receives an Image Data Request message it will respond with an Image
Data Response message. The message elements contained within the
Image Data Request is required in order to determine the intent of
the request. Note that only one message element may be present in
any given Image Data Request message.
The decision that new firmware is to downloaded to the WTP can occur
in one of two methods:
When the WTP joins the AC, and each exchange their software
revision, the WTP may opt to initiate a firmware download by
sending an Image Data Request, which contains an Image Filename
message element.
Once the WTP is in the CAPWAP state, it is possible for the AC to
cause the WTP to initiate a firmware download by initiating an
Image Data Request, with the Initiate Download message element.
The WTP would then transmit the Image Filename message element to
start the download process.
Regardless of how the download was initiated, once the AC receives an
Image Data Request with the Image Filename message element, it begins
the transfer process by transmitting its own request with the Image
Data message element. This continues until the whole firmware image
has been transfered.
The following message elements MAY be included in the Image Data
Request Message.
o Image Data, see Section 4.4.23
o Image Filename, see Section 4.4.24
o Initiate Download, see Section 4.4.25
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9.2. Image Data Response
The Image Data Response message acknowledges the Image Data Request
message.
An Image Data Response message is sent in response to a received
Image Data Request message. Its purpose is to acknowledge the
receipt of the Image Data Request message.
The Image Data Response message carries no message elements.
No action is necessary on receipt.
9.3. Reset Request
The Reset Request message is used to cause a WTP to reboot.
A Reset Request message is sent by an AC to cause a WTP to
reinitialize its operation.
The Reset Request carries no message elements.
When a WTP receives a Reset Request it will respond with a Reset
Response and then reinitialize itself.
9.4. Reset Response
The Reset Response message acknowledges the Reset Request message.
A Reset Response message is sent by the WTP after receiving a Reset
Request message.
The Reset Response message carries no message elements. Its purpose
is to acknowledge the receipt of the Reset Request message.
When an AC receives a Reset Response message, it is notified that the
WTP will reinitialize its operation.
9.5. WTP Event Request
WTP Event Request message is used by a WTP to send information to its
AC. The WTP Event Request message may be sent periodically, or sent
in response to an asynchronous event on the WTP. For example, a WTP
MAY collect statistics and use the WTP Event Request message to
transmit the statistics to the AC.
When an AC receives a WTP Event Request message it will respond with
a WTP Event Response message.
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The WTP Event Request message MUST contain one of the message
elements listed below, or a message element that is defined for a
specific wireless technology.
o Decryption Error Report, see Section 4.4.14
o Duplicate IPv4 Address, see Section 4.4.20
o Duplicate IPv6 Address, see Section 4.4.21
9.6. WTP Event Response
The WTP Event Response message acknowledges receipt of the WTP Event
Request message.
A WTP Event Response message issent by an AC after receiving a WTP
Event Request message.
The WTP Event Response message carries no message elements.
9.7. Data Transfer Request
The Data Transfer Request message is used to deliver debug
information from the WTP to the AC.
Data Transfer Request messages are sent by the WTP to the AC when the
WTP determines that it has important information to send to the AC.
For instance, if the WTP detects that its previous reboot was caused
by a system crash, it can send the crash file to the AC. The remote
debugger function in the WTP also uses the Data Transfer Request
message to send console output to the AC for debugging purposes.
When the AC receives a Data Transfer Request message it responds to
the WTP ith a Data Transfer Response message. The AC MAY log the
information received.
The Data Transfer Request message MUST contain one of the message
elements listed below.
o Data Transfer Mode, see Section 4.4.13
o Data Transfer Data, see Section 4.4.12
9.8. Data Transfer Response
The Data Transfer Response message acknowledges the Data Transfer
Request message.
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A Data Transfer Response message is sent in response to a received
Data Transfer Request message. Its purpose is to acknowledge receipt
of the Data Transfer Request message.
The Data Transfer Response message carries no message elements.
Upon receipt of a Data Transfer Response message, the WTP transmits
more information, if more information is available.
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10. Mobile Session Management
Messages in this section are used by the AC to create, modify or
delete mobile station session state on the WTPs.
10.1. Mobile Config Request
The Mobile Config Request message is used to create, modify or delete
mobile session state on a WTP. The message is sent by the AC to the
WTP, and may contain one or more message elements. The message
elements for this CAPWAP control message include information that is
generally highly technology specific. Refer to the appropriate
binding section or document for the definitions of the messages
elements that may be used in this control message.
The following CAPWAP Control message elements MAY be included in the
Mobile Config Request message.
o Add Mobile Station, see Section 4.4.8
o Delete Mobile Station, see Section 4.4.17
10.2. Mobile Config Response
The Mobile Configuration Response message is used to acknowledge a
previously received Mobile Configuration Request message, and MUST
include a Result Code message element, see Section 4.4.29 which
indicates whether an error occurred on the WTP.
This message requires no special processing, and is only used to
acknowledge receipt of the Mobile Configuration Request message.
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11. IEEE 802.11 Binding
This section defines the extensions required for the CAPWAP protocol
to be used with the IEEE 802.11 protocol.
11.1. Split MAC and Local MAC Functionality
The CAPWAP protocol, when used with IEEE 802.11 devices, requires a
specific behavior from the WTP and the AC, to support the required
IEEE 802.11 protocol functions.
For both the Split and Local MAC approaches, the CAPWAP functions, as
defined in the taxonomy specification [Add reference], reside in the
AC.
11.1.1. Split MAC
This section shows the division of labor between the WTP and the AC
in a Split MAC architecture. Figure 3 shows the clear separation of
functionality among CAPWAP components.
Function Location
Distribution Service AC
Integration Service AC
Beacon Generation WTP
Probe Response Generation WTP
Power Mgmt/Packet Buffering WTP
Fragmentation/Defragmentation WTP/AC
Assoc/Disassoc/Reassoc AC
802.11e
Classifying AC
Scheduling WTP/AC
Queuing WTP
802.11i
802.1X/EAP AC
RSNA Key Management AC
802.11 Encryption/Decryption WTP/AC
Figure 3: Mapping of 802.11 Functions for Split MAC Architecture
The Distribution and Integration services reside on the AC, and
therefore all user data is tunneled between the WTP and the AC. As
noted above, all real-time IEEE 802.11 services, including the beacon
and probe response frames, are handled on the WTP.
All remaining IEEE 802.11 MAC management frames are supported on the
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AC, including the Association Request which allows the AC to be
involved in the access policy enforcement portion of the IEEE 802.11
protocol. The IEEE 802.1X and IEEE 802.11i key management function
are also located on the AC.
While the admission control component of IEEE 802.11e resides on the
AC, the real time scheduling and queuing functions are on the WTP.
Note this does not exclude the AC from providing additional policing
and scheduling functionality.
Note that in the following figure, the use of '( - )' indicates that
processing of the frames is done on the WTP.
Client WTP AC
Beacon
<-----------------------------
Probe Request
----------------------------( - )------------------------->
Probe Response
<-----------------------------
802.11 AUTH/Association
<--------------------------------------------------------->
Mobile Config Request[Add Mobile (Clear Text, 802.1X)]
<------------------------->
802.1X Authentication & 802.11i Key Exchange
<--------------------------------------------------------->
Mobile Config Request[Add Mobile (AES-CCMP, PTK=x)]
<------------------------->
802.11 Action Frames
<--------------------------------------------------------->
802.11 DATA (1)
<---------------------------( - )------------------------->
Figure 4: Split MAC Message Flow
Figure 4 provides an illustration of the division of labor in a Split
MAC architecture. In this example, a WLAN has been created that is
configured for IEEE 802.11i, using AES-CCMP for privacy. The
following process occurs:
o The WTP generates the IEEE 802.11 beacon frames, using information
provided to it through the Add WLAN (see Section Section 11.10.1)
message element.
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o The WTP processes the probe request and responds with a
corresponding probe response. The probe request is then forwarded
to the AC for optional processing.
o The WTP forwards the IEEEE 802.11 Authentication and Association
frames to the AC, which is responsible for responding to the
client.
o Once the association is complete, the AC transmits an CAPWAP Add
Mobile Station request to the WTP (see Section Section 4.4.8. In
the above example, the WLAN is configured for IEEE 802.1X, and
therefore the '802.1X only' policy bit is enabled.
o If the WTP is providing encryption/decryption services, once the
client has completed the IEEE 802.11i key exchange, the AC
transmits another Add Mobile request to the WTP, stating the
security policy to enforce for the client (in this case AES-CCMP),
as well as the encryption key to use. If encryption/decryption is
handled in the AC, the Add Mobile Station request would have the
encryption policy set to "Clear Text".
o The WTP forwards any 802.11 Action frames received to the AC.
o All client data frames are tunneled between the WTP and the AC.
Note that the WTP is responsible for encrypting and decrypting
frames, if it was indicated in the Add Mobile request.
11.1.2. Local MAC
This section shows the division of labor between the WTP and the AC
in a Local MAC architecture. Figure 5 shows the clear separation of
functionality among CAPWAP components.
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Function Location
Distribution Service WTP
Integration Service WTP
Beacon Generation WTP
Probe Response WTP
Power Mgmt/Packet Buffering WTP
Fragmentation/Defragmentation WTP
Assoc/Disassoc/Reassoc WTP
802.11e
Classifying WTP
Scheduling WTP
Queuing WTP
802.11i
802.1X/EAP AC
RSNA Key Management AC
802.11 Encryption/Decryption WTP
Figure 5: Mapping of 802.11 Functions for Local AP Architecture
Given the Distribution and Integration Services exist on the WTP,
client data frames are not forwarded to the AC, with the exception
listed in the following paragraphs.
While the MAC is terminated on the WTP, it is necessary for the AC to
be aware of mobility events within the WTPs. As a consequence, the
WTP MUST forward the IEEE 802.11 Association Requests to the AC, and
the AC MAY reply with a failed Association Response if it deems it
necessary.
The IEEE 802.1X and RSNA Key Management function resides in the AC.
Therefore, the WTP MUST forward all IEEE 802.1X/RSNA Key Management
frames to the AC and forward the associated responses to the station.
Note that in the following figure, the use of '( - )' indicates that
processing of the frames is done on the WTP.
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Client WTP AC
Beacon
<-----------------------------
Probe
<---------------------------->
802.11 AUTH
<-----------------------------
802.11 Association
<---------------------------( - )------------------------->
Mobile Config Request[Add Mobile (Clear Text, 802.1X)]
<------------------------->
802.1X Authentication & 802.11i Key Exchange
<--------------------------------------------------------->
802.11 Action Frames
<--------------------------------------------------------->
Mobile Config Request[Add Mobile (AES-CCMP, PTK=x)]
<------------------------->
802.11 DATA
<----------------------------->
Figure 6: Local MAC Message Flow
Figure 6 provides an illustration of the division of labor in a Local
MAC architecture. In this example, a WLAN has been created that is
configured for IEEE 802.11i, using AES-CCMP for privacy. The
following process occurs:
o The WTP generates the IEEE 802.11 beacon frames, using information
provided to it through the Add WLAN (see Section 11.10.1) message
element.
o The WTP processes the probe request and responds with a
corresponding probe response.
o The WTP forwards the IEEE 802.11 Authentication and Association
frames to the AC, which is responsible for responding to the
client.
o Once the association is complete, the AC transmits an CAPWAP Add
Mobile Station message element to the WTP (see Section
Section 4.4.8. In the above example, the WLAN is configured for
IEEE 802.1X, and therefore the '802.1X only' policy bit is
enabled.
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o The WTP forwards all IEEE 802.1X and IEEE 802.11i key exchange
messages to the AC for processing.
o The AC transmits another Add Mobile Station message element to the
WTP, stating the security policy to enforce for the client (in
this case AES-CCMP), as well as the encryption key to use. The
Add Mobile Station message element MAY include a VLAN name, which
when present is used by the WTP to identify the VLAN on which the
user's data frames are to be bridged.
o The WTP forwards any IEEE 802.11 Action frames received to the AC.
11.2. Roaming Behavior
It is important that CAPWAP implementations react properly to mobile
devices associating to the networks in how they generate Add Mobile
and Delete Mobile messages. This section expands upon the examples
provided in the previous section, and describes how the CAPWAP
control protocol is used in order to provide secure roaming.
Once a client has successfully associated with the network in a
secure fashion, it is likely to attempt to roam to another WTP.
Figure 7 shows an example of a currently associated station moving
from its "Old WTP" to a "new WTP". The figure is useful for multiple
different security policies, including IEEE 802.1X and dynamic WEP
keys, WPA or even WPA2 both with key caching (where the IEEE 802.1x
exchange would be bypassed) and without.
Client Old WTP WTP AC
Association Request/Response
<--------------------------------------( - )-------------->
Mobile Config Request[Add Mobile (Clear Text, 802.1X)]
<---------------->
802.1X Authentication (if no key cache entry exists)
<--------------------------------------( - )-------------->
802.11i 4-way Key Exchange
<--------------------------------------( - )-------------->
Mobile Config Request[Delete Mobile]
<---------------------------------->
Mobile Config Request[Add Mobile (AES-CCMP, PTK=x)]
<---------------->
Figure 7: Client Roaming Example
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11.3. Group Key Refresh
Periodically, the Group Key (GTK)for the BSS needs to be updated.
The AC uses an EAPoL frame to update the group key for each STA in
the BSS. While the AC is updating the GTK, each L2 broadcast frame
transmitted to the BSS needs to be duplicated and transmitted using
both the current GTK and the new GTK. Once the GTK update process
has completed, broadcast frames transmitted to the BSS will be
encrypted using the new GYT
In the case of Split MAC, the AC needs to duplicate all broadcast
packets and update the key index so that the packet is transmitted
using both the current and new GTK to ensure that all STA's in the
BSS receive the broadcast frames. In the case of local MAC, the WTP
needs to duplicate and transmit broadcast frames using the
appropriate index to ensure that all STA's in the BSS continue to
receive broadcast frames.
The Group Key update procedure is given in the following figure. The
AC will signal the update to the GTK using an 802.11 Configuration
Request frame with the new GTK, its index, and the Key Status set to
3 (begin GTK update). The AC will then begin updating the GTK for
each STA. During this time, the AC (for Split MAC) or WTP (for Local
MAC) must duplicate broadcast packets and transmit them encrypted
with both the current and new GTK. When the AC has completed the GTK
update to all STA's in the BSS, the AC must transmit an 802.11
Configuration Request frame containing the new GTK, its index, and
the Key Status set to 4 (GTK update complete).
Client WTP AC
802.11 Config Request ( Update WLAN (GTK, GTK Index, GTK Start)
<----------------------------------------------
802.1X EAPoL (GTK Message 1)
<-------------( - )-------------------------------------------
802.1X EAPoL (GTK Message 2)
-------------( - )------------------------------------------->
802.11 Config Request ( Update WLAN (GTK, GTK Index, GTK Complete)
<---------------------------------------------
Figure 8: Group Key Update Procedure
11.4. Transport specific bindings
All CAPWAP transports have the following IEEE 802.11 specific
bindings:
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Payload encapsulation The CAPWAP protocol defines the CAPWAP data
frame, which is used to encapsulate a wireless payload. For IEEE
802.11, the IEEE 802.11 header and payload are encapsulated
(excluding the IEEE 802.11 FCS checksum). The IEEE 802.11 FCS
checksum is handled by the WTP. This allows the WTP to validate a
frame prior to sending it to the AC. Similarly, when an AC wishes
to transmit a frame towards a station, the WTP computes and adds
the FCS checksum.
CAPWAP Header Reserved field The reserved CAPWAP header field (see
figure Section 4.1) is only used with CAPWAP data frames, and it
serves two purposes, depending upon the direction of the frame.
For packets from the WTP to the AC, the field uses the format
described in the IEEE 802.11 Frame Info" field. However, for
frames sent by the AC to the WTP, the format used is described in
described in the Destination WLANs field.
IEEE 802.11 Frame Info When an CAPWAP data frame is received from a
station over the air, it is encapsulated and this field is used to
include radio and PHY specific information associated with the
frame.
When used with the IEEE 802.11 binding, the field follows the
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RSSI | SNR | Data Rate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RSSI: RSSI is a signed, 8-bit value. It is the received signal
strength indication, in dBm.
SNR: SNR is a signed, 8-bit value. It is the signal to noise
ratio of the received IEEE 802.11 frame, in dB.
Data Rate: The data rate field is a 16 bit unsigned value. The
contents of the field is set to 1/10th of the data rate of the
packet received by the WTP. For instance, a packet received at
5.5Mbps would be set to 55, while 11Mbps would be set to 110.
Destination WLANs The Destination WLAN field is used to specify the
target WLANs for a given frame, and is only used with broadcast
and multicast frames. This field allows the AC to transmit a
single broadcast or multicast frame to the WTP, and allows the WTP
to perform the necessary frame replication services. The field
uses the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WLAN | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
WLAN: This bit field indicates the WLAN ID (see section
Section 11.10.1) which the WTP will transmit the associated
frame on. For instance, if a multicast packet is to be
transmitted on WLANs 1 and 3, bits 1 and 3 of this field would
be enabled. Note this field is to be set to zero for unicast
packets and is unused if the WTP is not providing encryption
services.
Reserved: This field MUST be set to zero.
11.5. BSSID to WLAN ID Mapping
The CAPWAP protocol allows the WTP to assign BSSIDs upon creation of
a WLAN (see Section Section 11.10.1). While manufacturers are free
to assign BSSIDs using any arbitrary mechanism, it is advised that
where possible the BSSIDs are assigned as a contiguous block.
When assigned as a block, implementations can still assign any of the
available BSSIDs to any WLAN. One possible method is for the WTP to
assign the address using the following algorithm: base BSSID address
+ WLAN ID.
The WTP communicates the maximum number of BSSIDs that it supports
during the Config Request within the IEEE 802.11 WTP WLAN Radio
Configuration message element (see Section 11.10.24).
11.6. Quality of Service for Control Messages
It is recommended that IEEE 802.11 MAC management frames be sent by
both the AC and the WTP with appropriate Quality of Service values,
ensuring that congestion in the network minimizes occurrences of
packet loss. Therefore, a Quality of Service enabled CAPWAP device
should use:
802.1P: The precedence value of 6 SHOULD be used for all IEEE 802.11
MAC management frames, except for Probe Requests which SHOULD use
4.
DSCP: The DSCP tag value of 46 SHOULD be used for all IEEE 802.11
MAC management frames, except for Probe Requests which SHOULD use
34.
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11.7. IEEE 802.11 Specific CAPWAP Control Messages
This section defines CAPWAP Control Messages that are specific to the
IEEE 802.11 binding. The two messages are defined as IEEE 802.11
WLAN Config Request and IEEE 802.11 WLAN Config Response. See
Section 4.3.1.1
The valid message types for IEEE 802.11 specific control messages are
listed below. The IANA Enterprise number used with these messages is
13277
CAPWAP Control Message Message Type
Value
IEEE 802.11 WLAN Config Request 3398912
IEEE 802.11 WLAN Config Response 3398913
11.7.1. IEEE 802.11 WLAN Config Request
The IEEE 802.11 WLAN Configuration Request is sent by the AC to the
WTP in order to change services provided by the WTP. This control
message is used to either create, update or delete a WLAN on the WTP.
The IEEE 802.11 WLAN Configuration Request is sent as a result of
either some manual admistrative process (e.g., deleting a WLAN), or
automatically to create a WLAN on a WTP. When sent automatically to
create a WLAN, this control message is sent after the CAPWAP
Configure Update Request message has been received by the WTP.
Upon receiving this control message, the WTP will modify the
necessary services, and transmit an IEEE 802.11 WLAN Configuration
Response.
A WTP MAY provide service for more than one WLAN, therefore every
WLAN is identified through a numerical index. For instance, a WTP
that is capable of supporting up to 16 SSIDs, could accept up to 16
IEEE 802.11 WLAN Configuration Request messages that include the Add
WLAN message element.
Since the index is the primary identifier for a WLAN, an AC MAY
attempt to ensure that the same WLAN is identified through the same
index number on all of its WTPs. An AC that does not follow this
approach MUST find some other means of maintaining a WLAN Identifier
to SSID mapping table.
The following message elements may be included in the IEEE 802.11
WLAN Config Request message. Only one message element MUST be
present.
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o IEEE 802.11 Add WLAN, see Section 11.10.1
o IEEE 802.11 Delete WLAN, see Section 11.10.5
o IEEE 802.11 Update WLAN, see Section 11.10.21
o IEEE 802.11 Information Element, see Section 11.10.7
11.7.2. IEEE 802.11 WLAN Config Response
The IEEE 802.11 WLAN Configuration Response is sent by the AC to the
WTP as an acknowledgement of the receipt of an IEEE 802.11 WLAN
Configuration Request.
The following message elements may be included in the IEEE 802.11
WLAN Config Request message. Only one message element MUST be
present.
o IEEE 802.11 Assigned WTP BSSID, see Section 11.10.3
11.8. Data Message bindings
There are no CAPWAP Data Message bindings for IEEE 802.11.
11.9. Control Message bindings
This section describes he IEEE 802.11 specific message elements
included in CAPWAP Control Messages.
11.9.1. Mobile Config Request
The following IEEE 802.11 specific message elements MAY used with the
CAPWAP Mobile Config Request message.
o IEEE 802.11 Mobile, see Section 11.10.11
o IEEE 802.11 Mobile Session Key, see Section 11.10.12
o Station QOS Profile, see Section 11.10.25
11.9.2. WTP Event Request
The following IEEE 802.11 specific message elements may be included
in the CAPWAP WTP Event Request message.
o IEEE 802.11 MIC Countermeasures, see Section 11.10.9
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o IEEE 802.11 Statistics, see Section 11.10.16
o IEEE 802.11 WTP Radio Fail Alarm Indication, see Section 11.10.23
11.9.3. Configuration Messages
This section defines the IEEE 802.11 Message Elements which MAY be
included in the Configuration Status, Configuration Status Response,
Configuration Update Request and Mobile Config Request CAPWAP control
meessages. The binding of message elements to CAPWAP control
messages is shown below:
Conf Conf Conf Mobile
Message Element Stat Stat Upd Config Req
Msg Resp Msg Msg
IEEE 802.11 Antenna X X X
IEEE 802.11 Broadcast Probe Mode X X
IEEE 802.11 Direct Sequence Control X X X
IEEE 802.11 MAC Operation X X X
IEEE 802.11 MIC Error Report From Mobile X
IEEE 802.11 Mobile Session Key X
IEEE 802.11 Multi-domain Capability X X X
IEEE 802.11 OFDM Control X X X
IEEE 802.11 Rate Set X X
IEEE 802.11 Supported Rates X X
IEEE 802.11 Tx Power X X X
IEEE 802.11 Tx Power Level X
IEEE 802.11 Update Mobile QoS X
IEEE 802.11 WTP Mode and Type X? X
IEEE 802.11 WTP Quality of Service X X
IEEE 802.11 WTP Radio Configuration X X X
11.10. IEEE 802.11 Message Element Definitions
11.10.1. IEEE 802.11 Add WLAN
The Add WLAN message element is used by the AC to define a wireless
LAN on the WTP. The inclusion of this message element MUST also
include IEEE 802.11 Information Element message elements, containing
the following 802.11 IEs:
Power Capability information element
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WPA information element
RSN information element
EDCA Parameter Set information element
QoS Capability information element
WMM information element
The message element uses the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Index | Key Status | QoS | Auth Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Mode | Tunnel Mode | Suppress SSID | SSID ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1024 for IEEE 802.11 Add WLAN
Length: >= 49
Radio ID: An 8-bit value representing the radio.
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WLAN ID: An 8-bit value specifying the WLAN Identifier.
Reserved: A 16-bit value that MUST be set to zero.
Encryption Policy: A 32-bit value specifying the encryption scheme
to apply to traffic to and from the mobile station. The
applicability of the encryption policy depends upon the security
policy. For static WEP keys, which is true when the 'Shared Key'
bit is set, this encryption policy is relevant for both unicast
and multicast traffic. For encryption schemes that employ a
separate encryption key for unicast and multicast traffic, the
encryption policy defined here only applies to multicast data. In
these scenarios, the unicast encryption policy is communicated via
the Add Mobile Station (Section 4.4.8).
0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using standard 104 bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must be
encrypted using standard 40 bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using standard 128 bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using 128 bit AES CCMP [7]
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [24]
Key: A 32 byte Session Key to use with the encryption policy.
Key-Index: The Key Index associated with the key.
Key Status: A 1 byte value that specifies the state and usage of the
key that has been included. The following values describe the key
usage and its status:
0 - A value of zero, with the 'Encryption Policy' field set to any
value other than 'Clear Text' means that the WLAN uses per-station
encryption keys, and therefore the key in the 'Key' field is only
used for multicast traffic.
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1 - When set to one, the WLAN employs a shared WEP key, also known as
a static WEP key, and uses the encryption key for both unicast and
multicast traffic for all stations.
2 - The value of 2 indicates that the AC will begin rekeying the GTK
with the STA's in the BSS. It is only valid when IEEE 802.11i is
enabled as the security policy for the BSS.
3 - The value of 3 indicates that the AC has completed rekeying the
GTK and broadcast packets no longer need to be duplicated and
transmitted with both GTK's.
QOS: An 8-bit value specifying the QoS policy to enforce for the
station.
The following values are supported:
0 - Best Effort
1 - Video
2 - Voice
3 - Background
Auth Type: An 8-bit value specifying the supported authentication
type.
The following values are supported:
0 - Open System
1 - WEP Shared Key
2 - WPA/WPA2 802.1X
3 - WPA/WPA2 PSK
MAC Mode: This field specifies whether the WTP should support the
WLAN in Local or Split MAC modes. Note that the AC MUST NOT
request a mode of operation that was not advertised by the WTP
during the discovery process (see section Section 4.4.38). The
following values are supported:
0 - Local-MAC: Service for the WLAN is to be provided in Local
MAC mode.
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1 - Split-MAC: Service for the WLAN is to be provided in Split
MAC mode.
Tunnel Mode: This field specifies the tunneling type to be used for
all stations associated with the WLAN. Note that the AC MUST NOT
request a mode of operation that was not advertised by the WTP
during the discovery process (see section Section 4.4.36). The
following values are supported:
0 - Local Bridging: All user traffic is to be locally bridged.
1 - 802.3 Tunnel: All user traffic is to be tunneled to the AC in
802.3 format (see section Section 4.2).
2 - 802.11 Bridging: All user traffic is to be tunneled to the AC
in 802.11 format.
Supress SSID: A boolean indicating whether the SSID is to be
advertised by the WTP. A value of zero supresses the SSID in the
802.11 Beacon and Probe Response frames, while a value of one will
cause the WTP to populate the field.
SSID: The SSID attribute is the service set identifier that will be
advertised by the WTP for this WLAN.
11.10.2. IEEE 802.11 Antenna
The antenna message element is communicated by the WTP to the AC to
provide information on the antennas available. The AC MAY use this
element to reconfigure the WTP's antennas. The value contains the
following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Diversity | Combiner | Antenna Cnt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Antenna Selection [0..N] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1025 for IEEE 802.11 Antenna
Length: >= 5
Radio ID: An 8-bit value representing the radio to configure.
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Diversity: An 8-bit value specifying whether the antenna is to
provide receive diversity. The following values are supported:
0 - Disabled
1 - Enabled (may only be true if the antenna can be used as a
receive antenna)
Combiner: An 8-bit value specifying the combiner selection. The
following values are supported:
1 - Sectorized (Left)
2 - Sectorized (Right)
3 - Omni
4 - MIMO
Antenna Count: An 8-bit value specifying the number of Antenna
Selection fields.
Antenna Selection: One 8-bit antenna configuration value per antenna
in the WTP. The following values are supported:
1 - Internal Antenna
2 - External Antenna
11.10.3. IEEE 802.11 Assigned WTP BSSID
The IEEE 802.11 Assigned WTP BSSID is only included by the WTP when
the IEEE 802.11 WLAN Config Request included the IEEE 802.11 Add WLAN
message element. The value field of this message element contains
the BSSID that has been assigned by the WTP, which allows the WTP to
perform its own BSSID assignment.
The WTP is free to assign the BSSIDs the way it sees fit, but it is
highly recommended that the WTP assign the BSSID using the following
algorithm: BSSID = {base BSSID} + WLAN ID.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 1026 for IEEE 802.11 Assigned WTP BSSID
Length: 6
BSSID: The BSSID assigned by the WTP for the WLAN created as a
result of receiving an IEEE 802.11 Add WLAN.
11.10.4. IEEE 802.11 Broadcast Probe Mode
The Broadcast Probe Mode message element indicates whether a WTP will
respond to NULL SSID probe requests. Since broadcast NULL probes are
not sent to a specific BSSID, the WTP cannot know which SSID the
sending station is querying. Therefore, this behavior must be global
to the WTP.
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+
Type: 1027 for IEEE 802.11 Broadcast Probe Mode
Length: 1
Status: An 8-bit boolean indicating the status of whether a WTP
shall response to a NULL SSID probe request. A value of zero
disables NULL SSID probe response, while a value of one enables
it.
11.10.5. IEEE 802.11 Delete WLAN
The delete WLAN message element is used to inform the WTP that a
previously created WLAN is to be deleted. The value contains the
following fields:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1028 for IEEE 802.11 Delete WLAN
Length: 3
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Radio ID: An 8-bit value representing the radio
WLAN ID: A 16-bit value specifying the WLAN Identifier
11.10.6. IEEE 802.11 Direct Sequence Control
The direct sequence control message element is a bi-directional
element. When sent by the WTP, it contains the current state. When
sent by the AC, the WTP MUST adhere to the values. This element is
only used for 802.11b radios. The value has the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Chan | Current CCA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Energy Detect Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1029 for IEEE 802.11 Direct Sequence Control
Length: 8
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Channel: This attribute contains the current operating
frequency channel of the DSSS PHY.
Current CCA: The current CCA method in operation. Valid values are:
1 - energy detect only (edonly)
2 - carrier sense only (csonly)
4 - carrier sense and energy detect (edandcs)
8 - carrier sense with timer (cswithtimer)
16 - high rate carrier sense and energy detect (hrcsanded)
Energy Detect Threshold: The current Energy Detect Threshold being
used by the DSSS PHY.
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11.10.7. IEEE 802.11 Information Element
The IEEE 802.11 Information Element is used to communicate any IE
defined in the IEEE 802.11 protocol. The data field contains the raw
IE as it would be included within an IEEE 802.11 MAC management
message.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|B|P| Flags | Info Element
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type: 1030 for IEEE 802.11 Information Element
Length: >= 2
B: When set, the WTP is to include the information element in
beacons associated with the WLAN.
P: When set, the WTP is to include the information element in probe
responses associated with the WLAN.
Flags: Reserved field and MUST be set to zero.
Info Element: The IEEE 802.11 Information Element, which includes
the type, length and value field.
11.10.8. IEEE 802.11 MAC Operation
The MAC operation message element is sent by the AC to set the 802.11
MAC parameters on the WTP. The value contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | RTS Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Short Retry | Long Retry | Fragmentation Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tx MSDU Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rx MSDU Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 1031 for IEEE 802.11 MAC Operation
Length: 16
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
RTS Threshold: This attribute indicates the number of octets in an
MPDU, below which an RTS/CTS handshake MUST NOT be performed. An
RTS/CTS handshake MUST be performed at the beginning of any frame
exchange sequence where the MPDU is of type Data or Management,
the MPDU has an individual address in the Address1 field, and the
length of the MPDU is greater than this threshold. Setting this
attribute to be larger than the maximum MSDU size MUST have the
effect of turning off the RTS/CTS handshake for frames of Data or
Management type transmitted by this STA. Setting this attribute
to zero MUST have the effect of turning on the RTS/CTS handshake
for all frames of Data or Management type transmitted by this STA.
The default value of this attribute MUST be 2347.
Short Retry: This attribute indicates the maximum number of
transmission attempts of a frame, the length of which is less than
or equal to RTSThreshold, that MUST be made before a failure
condition is indicated. The default value of this attribute MUST
be 7.
Long Retry: This attribute indicates the maximum number of
transmission attempts of a frame, the length of which is greater
than dot11RTSThreshold, that MUST be made before a failure
condition is indicated. The default value of this attribute MUST
be 4.
Fragmentation Threshold: This attribute specifies the current
maximum size, in octets, of the MPDU that MAY be delivered to the
PHY. An MSDU MUST be broken into fragments if its size exceeds
the value of this attribute after adding MAC headers and trailers.
An MSDU or MMPDU MUST be fragmented when the resulting frame has
an individual address in the Address1 field, and the length of the
frame is larger than this threshold. The default value for this
attribute MUST be the lesser of 2346 or the aMPDUMaxLength of the
attached PHY and MUST never exceed the lesser of 2346 or the
aMPDUMaxLength of the attached PHY. The value of this attribute
MUST never be less than 256.
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Tx MSDU Lifetime: This attribute speficies the elapsed time in TU,
after the initial transmission of an MSDU, after which further
attempts to transmit the MSDU MUST be terminated. The default
value of this attribute MUST be 512.
Rx MSDU Lifetime: This attribute specifies the elapsed time in TU,
after the initial reception of a fragmented MMPDU or MSDU, after
which further attempts to reassemble the MMPDU or MSDU MUST be
terminated. The default value MUST be 512.
11.10.9. IEEE 802.11 MIC Countermeasures
The MIC Countermeasures message element is sent by the WTP to the AC
to indicate the occurrence of a MIC failure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1032 for IEEE 802.11 MIC Countermeasures
Length: 8
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP.
WLAN ID: This 8-bit unsigned integer includes the WLAN Identifier,
on which the MIC failure occurred.
MAC Address: The MAC Address of the mobile station that caused the
MIC failure.
11.10.10. IEEE 802.11 MIC Error Report From Mobile
The MIC Error Report From Mobile message element is sent by an AC to
an WTP when it receives a MIC failure notification, via the Error bit
in the EAPOL-Key frame.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Client MAC Address | BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1033 for IEEE 802.11 MIC Error Report From Mobile
Length: 14
Client MAC Address: The Client MAC Address of the station reporting
the MIC failure.
BSSID: The BSSID on which the MIC failure is being reported.
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP
WLAN ID: The WLAN ID on which the MIC failure is being reported.
11.10.11. IEEE 802.11 Mobile
The IEEE 802.11 Mobile message element accompanies the Add Mobile
message element, and is used to deliver IEEE 802.11 station policy
from the AC to the WTP.
The latest IEEE 802.11 Mobile message element overrides any
previously received message elements.
If the QoS field is set, the WTP MUST observe and provide policing of
the 802.11e priority tag to ensure that it does not exceed the value
provided by the AC.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Association ID | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capabilities | WLAN ID |Supported Rates
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 1034 for Add IEEE 802.11 Mobile
Length: >= 8
Radio ID: An 8-bit value representing the radio
Association ID: A 16-bit value specifying the IEEE 802.11
Association Identifier
Flags: The Flags field MUST be set to zero
Capabilities: A 16-bit field containing the IEEE 802.11 capabilities
to use with the mobile.
WLAN ID: An 8-bit value specifying the WLAN Identifier
Supported Rates: The variable length field containing the supported
rates to be used with the mobile station.
11.10.12. IEEE 802.11 Mobile Session Key
The Mobile Session Key Payload message element is sent when the AC
determines that encryption of a mobile station must be performed in
the WTP. This message element MUST NOT be present without the IEEE
802.11 Mobile (see Section 11.10.11) message element, and MUST NOT be
sent if the WTP had not specifically advertised support for the
requested encryption scheme.
If the IEEE 802.11 Mobile Session Key message element's EAP-Only bit
is set, the WTP MUST drop all IEEE 802.11 packets that do not contain
EAP packets. Note that when EAP-Only is set, the Encryption Policy
field MAY be set, and therefore it is possible to inform a WTP to
only accept encrypted EAP packets. Once the mobile station has
successfully completed EAP authentication, the AC must send a new Add
Mobile message element to remove the EAP Only restriction, and
optionally push the session key down to the WTP.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |E|C| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pairwise TSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pairwise TSC | Pairwise RSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pairwise RSC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Key...
+-+-+-+-+-+-+-+-
Type: 1035 for IEEE 802.11 Mobile Session Key
Length: >= 25
MAC Address: The mobile station's MAC Address
Flags: A 16 bit field, whose unused bits MUST be set to zero. The
following bits are defined:
E: The one bit EAP-Only field is set by the AC to inform the WTP
that is MUST NOT accept any 802.11 data frames, other than IEEE
802.1X frames. This is the equivalent of the WTP's IEEE 802.1X
port for the mobile station to be in the closed state. When
set, the WTP MUST drop any non-IEEE 802.1X packets it receives
from the mobile station.
C: The one bit field is set by the AC to inform the WTP that
encryption services will be provided by the AC. When set, the
WTP SHOULD police frames received from stations to ensure that
they comply to the stated encryption policy, but does not need
to take specific cryptographic action on the frame. Similarly,
for transmitted frames, the WTP only needs to forward already
encrypted frames.
Encryption Policy: The policy field informs the WTP how to handle
packets from/to the mobile station. The following values are
supported:
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0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using standard 104 bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must be
encrypted using standard 40 bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using standard 128 bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using 128 bit AES CCMP [7]
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [24]
Pairwise TSC: The 6 byte Transmit Sequence Counter (TSC) field to
use for unicast packets transmitted to the mobile.
Pairwise RSC: The 6 byte Receive Sequence Counter (RSC) to use for
unicast packets received from the mobile.
Session Key: The session key the WTP is to use when encrypting
traffic to/from the mobile station. For dynamically created keys,
this is commonly known as a Pairwise Transient Key (PTK).
11.10.13. IEEE 802.11 Multi-domain Capability
The multi-domain capability message element is used by the AC to
inform the WTP of regulatory limits. The value contains the
following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | First Channel # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Channels | Max Tx Power Level |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1036 for IEEE 802.11 Multi-Domain Capability
Length: 8
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Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
First Channnel #: This attribute indicates the value of the lowest
channel number in the subband for the associated domain country
string.
Number of Channels: This attribute indicates the value of the total
number of channels allowed in the subband for the associated
domain country string.
Max Tx Power Level: This attribute indicates the maximum transmit
power, in dBm, allowed in the subband for the associated domain
country string.
11.10.14. IEEE 802.11 OFDM Control
The OFDM control message element is a bi-directional element. When
sent by the WTP, it contains the current state. When sent by the AC,
the WTP MUST adhere to the values. This element is only used for
802.11a radios. The value contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Chan | Band Support |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TI Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1037 for IEEE 802.11 OFDM Control
Length: 8
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Channel: This attribute contains the current operating
frequency channel of the OFDM PHY.
Band Supported: The capability of the OFDM PHY implementation to
operate in the three U-NII bands. Coded as an integer value of a
three bit field as follows:
capable of operating in the lower (5.15-5.25 GHz) U-NII band
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capable of operating in the middle (5.25-5.35 GHz) U-NII band
capable of operating in the upper (5.725-5.825 GHz) U-NII band
For example, for an implementation capable of operating in the
lower and mid bands this attribute would take the value
TI Threshold: The Threshold being used to detect a busy medium
(frequency). CCA MUST report a busy medium upon detecting the
RSSI above this threshold.
11.10.15. IEEE 802.11 Rate Set
The rate set message element value is sent by the AC and contains the
supported operational rates. It contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Rate Set...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1038 for IEEE 802.11 Rate Set
Length: >= 3
Radio ID: An 8-bit value representing the radio to configure.
Rate Set: The AC generates the Rate Set that the WTP is to include
in it's Beacon and Probe messages. The length of this field is
between 2 and 8 bytes.
11.10.16. IEEE 802.11 Statistics
The statistics message element is sent by the WTP to transmit it's
current statistics. The value contains the following fields.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tx Fragment Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Tx Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Failed Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multiple Retry Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Duplicate Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTS Success Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTS Failure Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACK Failure Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rx Fragment Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast RX Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS Error Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tx Frame Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Decryption Errors |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1039 for Statistics
Length: 60
Radio ID: An 8-bit value representing the radio.
Tx Fragment Count: A 32-bit value representing the number of
fragmented frames transmitted.
Multicast Tx Count: A 32-bit value representing the number of
multicast frames transmitted.
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Failed Count: A 32-bit value representing the transmit excessive
retries.
Retry Count: A 32-bit value representing the number of transmit
retries.
Multiple Retry Count: A 32-bit value representing the number of
transmits that required more than one retry.
Frame Duplicate Count: A 32-bit value representing the duplicate
frames received.
RTS Success Count: A 32-bit value representing the number of
successfully transmitted Ready To Send (RTS).
RTS Failure Count: A 32-bit value representing the failed
transmitted RTS.
ACK Failure Count: A 32-bit value representing the number of failed
acknowledgements.
Rx Fragment Count: A 32-bit value representing the number of
fragmented frames received.
Multicast RX Count: A 32-bit value representing the number of
multicast frames received.
FCS Error Count: A 32-bit value representing the number of FCS
failures.
Decryption Errors: A 32-bit value representing the number of
Decryption errors that occurred on the WTP. Note that this field
is only valid in cases where the WTP provides encryption/
decryption services.
11.10.17. IEEE 802.11 Supported Rates
The supported rates message element is sent by the WTP to indicate
the rates that it supports. The value contains the following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Supported Rates...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 1040 for IEEE 802.11 Supported Rates
Length: >= 3
Radio ID: An 8-bit value representing the radio.
Supported Rates: The WTP includes the Supported Rates that its
hardware supports. The format is identical to the Rate Set
message element and is between 2 and 8 bytes in length.
11.10.18. IEEE 802.11 Tx Power
The Tx power message element value is bi-directional. When sent by
the WTP, it contains the current power level of the radio in
question. When sent by the AC, it contains the power level the WTP
MUST adhere to.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Current Tx Power |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1041 for IEEE 802.11 Tx Power
Length: 4
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
Current Tx Power: This attribute contains the transmit output power
in mW.
11.10.19. IEEE 802.11 Tx Power Level
The Tx power level message element is sent by the WTP and contains
the different power levels supported. The value contains the
following fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Num Levels | Power Level [n] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 1042 for IEEE 802.11 Tx Power Level
Length: >= 4
Radio ID: An 8-bit value representing the radio to configure.
Num Levels: The number of power level attributes.
Power Level: Each power level fields contains a supported power
level, in mW.
11.10.20. IEEE 802.11 Update Mobile QoS
The Update Mobile QoS message element is used to change the Quality
of Service policy on the WTP for a given mobile station.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | DSCP Tag | 802.1P Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1043 for IEEE 802.11 Update Mobile QoS
Length: 8
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP
MAC Address: The mobile station's MAC Address.
DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
802.1P Tag: The 802.1P precedence value to use if packets are to be
IEEE 802.1P tagged.
11.10.21. IEEE 802.11 Update WLAN
The Update WLAN message element is used by the AC to define a
wireless LAN on the WTP. The inclusion of this message element MUST
also include the IEEE 802.11 Information Element message element,
containing the following 802.11 IEs:
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Power Capability information element
WPA information element
RSN information element
EDCA Parameter Set information element
QoS Capability information element
WMM information element
The message element uses the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID |Encrypt Policy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encryption Policy | Key... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Index | Shared Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1044 for IEEE 802.11 Update WLAN
Length: 43
Radio ID: An 8-bit value representing the radio.
WLAN ID: A 16-bit value specifying the WLAN Identifier.
Encryption Policy: A 32-bit value specifying the encryption scheme
to apply to traffic to and from the mobile station. The
applicability of the encryption policy depends upon the security
policy. For static WEP keys, which is true when the 'Shared Key'
bit is set, this encryption policy is relevant for both unicast
and multicast traffic. For encryption schemes that employ a
separate encryption key for unicast and multicast traffic, the
encryption policy defined here only applies to multicast data. In
these scenarios, the unicast encryption policy is communicated via
the Add Mobile Station (Section 4.4.8).
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The following values are supported:
0 - Encrypt WEP 104: All packets to/from the mobile station must
be encrypted using standard 104 bit WEP.
1 - Clear Text: All packets to/from the mobile station do not
require any additional crypto processing by the WTP.
2 - Encrypt WEP 40: All packets to/from the mobile station must be
encrypted using standard 40 bit WEP.
3 - Encrypt WEP 128: All packets to/from the mobile station must
be encrypted using standard 128 bit WEP.
4 - Encrypt AES-CCMP 128: All packets to/from the mobile station
must be encrypted using 128 bit AES CCMP [7]
5 - Encrypt TKIP-MIC: All packets to/from the mobile station must
be encrypted using TKIP and authenticated using Michael [24]
Key: A 32 byte Session Key to use with the encryption policy.
Key-Index: The Key Index associated with the key.
Key Status: A 1 byte value that specifies the state and usage of the
key that has been included. The following values describe the key
usage and its status:
0 - A value of zero, with the 'Encryption Policy' field set to any
value other than 'Clear Text' means that the WLAN uses per-station
encryption keys, and therefore the key in the 'Key' field is only
used for multicast traffic.
1 - When set to one, the WLAN employs a shared WEP key, also known as
a static WEP key, and uses the encryption key for both unicast and
multicast traffic for all stations.
2 - The value of 2 indicates that the AC will begin rekeying the GTK
with the STA's in the BSS. It is only valid when IEEE 802.11i is
enabled as the security policy for the BSS.
3 - The value of 3 indicates that the AC has completed rekeying the
GTK and broadcast packets no longer need to be duplicated and
transmitted with both GTK's.
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11.10.22. IEEE 802.11 WTP Quality of Service
The WTP Quality of Service message element value is sent by the AC to
the WTP to communicate quality of service configuration information.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Tag Packets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1045 for IEEE 802.11 WTP Quality of Service
Length: >= 2
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP
Tag Packets: An value indicating whether CAPWAP packets should be
tagged with for QoS purposes. The following values are currently
supported:
0 - Untagged
1 - 802.1P
2 - DSCP
Immediately following the above header is the following data
structure. This data structure will be repeated five times; once
for every QoS profile. The order of the QoS profiles are Voice,
Video, Best Effort and Background.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Queue Depth | CWMin | CWMax |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CWMax | AIFS | Dot1P Tag | DSCP Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Queue Depth: The number of packets that can be on the specific QoS
transmit queue at any given time.
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CWMin: The Contention Window minimum value for the QoS transmit
queue.
CWMax: The Contention Window maximum value for the QoS transmit
queue.
AIFS: The Arbitration Inter Frame Spacing to use for the QoS
transmit queue.
Dot1P Tag: The 802.1P precedence value to use if packets are to be
802.1P tagged.
DSCP Tag: The DSCP label to use if packets are to be DSCP tagged.
11.10.23. IEEE 802.11 WTP Radio Fail Alarm Indication
The WTP Radio Fail Alarm Indication message element is sent by the
WTP to the AC when it detects a radio failure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Type | Status | Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1046 for WTP Radio Fail Alarm Indication
Length: 4
Radio ID: The Radio Identifier, typically refers to some interface
index on the WTP
Type: The type of radio failure detected. The following values are
supported:
1 - Receiver
2 - Transmitter
Status: An 8-bit boolean indicating whether the radio failure is
being reported or cleared. A value of zero is used to clear the
event, while a value of one is used to report the event.
Pad: Reserved field MUST be set to zero (0).
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11.10.24. IEEE 802.11 WTP Radio Configuration
The WTP WLAN radio configuration is used by the AC to configure a
Radio on the WTP, and by the WTP to deliver its radio configuration
to the AC. The message element value contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | Reserved | Num of BSSIDs | DTIM Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BSSID | Beacon Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Country Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1047 for IEEE 802.11 WTP WLAN Radio Configuration
Length: 16
Radio ID: An 8-bit value representing the radio to configure.
Reserved: MUST be set to zero
BSSID: The WLAN Radio's base MAC Address.
Number of BSSIDs: This attribute contains the maximum number of
BSSIDs supported by the WTP. This value restricts the number of
logical networks supported by the WTP, and is between 1 and 16.
DTIM Period: This attribute specifies the number of beacon intervals
that elapse between transmission of Beacons frames containing a
TIM element whose DTIM Count field is 0. This value is
transmitted in the DTIM Period field of Beacon frames.
Beacon Period: This attribute specifies the number of TU that a
station uses for scheduling Beacon transmissions. This value is
transmitted in Beacon and Probe Response frames.
Country Code: This attribute identifies the country in which the
station is operating. Special attention is required with use of
this field, as implementations which take action based on this
field could violate regulatory requirements. Some regulatory
bodies do permit configuration of the country code under certain
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restrictions, such as the FCC, when WTPs are certified as Software
Defined Radios.
The WTP and AC may ignore the value of this field, depending upon
regulatory requirements, for example to avoid classification as a
Software Defined Radio. When this field is used, the first two
octets of this string is the two character country code as
described in document ISO/IEC 3166- 1, and the third octet MUST
have the value 1, 2 or 3 as defined below. When the value of the
third octet is 255, the country code field is not used, and MUST
be ignored
1 an ASCII space character, if the regulations under which the
station is operating encompass all environments in the country,
2 an ASCII 'O' character, if the regulations under which the
station is operating are for an outdoor environment only, or
3 an ASCII 'I' character, if the regulations under which the
station is operating are for an indoor environment only
255 Country Code field is not used; ignore the field.
11.10.25. Station QoS Profile
The Station QoS Profile Payload message element contains the maximum
IEEE 802.11e priority tag that may be used by the station. Any
packet received that exceeds the value encoded in this message
element must either be dropped or tagged using the maximum value
permitted by to the user. The priority tag must be between zero (0)
and seven (7).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address | 802.1P Precedence Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 1048 for IEEE 802.11 Station QOS Profile
Length: 8
MAC Address: The mobile station's MAC Address
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802.1P Precedence Tag: The maximum 802.1P precedence value that the
WTP will allow in the TID field in the extended 802.11e QOS Data
header.
11.11. Technology Specific Message Element Values
This section lists IEEE 802.11 specific values for any generic CAPWAP
message elements which include fields whose values are technology
specific.
IEEE 802.11 uses the following values:
4 - Encrypt AES-CCMP 128: WTP supports AES-CCMP, as defined in [7].
5 - Encrypt TKIP-MIC: WTP supports TKIP and Michael, as defined in
[24].
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12. NAT Considerations
There are two specific situations in which a NAT system may be used
in conjunction with a CAPWAP-enabled system. The first consists of a
configuration where the WTP is behind a NAT system. Given that all
communication is initiated by the WTP, and all communication is
performed over IP using two UDP ports, the protocol easily traverses
NAT systems in this configuration.
The second configuration is one where the AC sits behind a NAT. Two
issues exist in this situation. First, an AC communicates its
interfaces, and associated WTP load on these interfaces, through the
WTP Manager Control IP Address. This message element is currently
mandatory, and if NAT compliance became an issue, it would be
possible to either:
1. Make the WTP Manager Control IP Address optional, allowing the WTP
to simply use the known IP Address. However, note that this
approach would eliminate the ability to perform load balancing of
WTP across ACs, and therefore is not the recommended approach.
2. Allow an AC to be able to configure a NAT'ed address for every
associated AC that would generally be communicated in the WTP
Manager Control IP Address message element.
3. Require that if a WTP determines that the AC List message element
consists of a set of IP Addresses that are different from the AC's
IP Address it is currently communicating with, then assume that
NAT is being enforced, and require that the WTP communicate with
the original AC's IP Address (and ignore the WTP Manager Control
IP Address message element(s)).
Another issue related to having an AC behind a NAT system is CAPWAP's
support for the CAPWAP Objective to allow the control and data plane
to be separated. In order to support this requirement, the CAPWAP
protocol defines the WTP Manager Data IP Address message element,
which allows the AC to inform the WTP that the CAPWAP data frames are
to be forwarded to a separate IP Address. This feature MUST be
disabled when an AC is behind a NAT. However, there is no easy way
to provide some default mechanism that satisfies both the data/
control separation and NAT objectives, as they directly conflict with
each other. As a consequence, user intervention will be required to
support such networks.
The CAPWAP protocol allows for all of the ACs identities supporting a
group of WTPs to be communicated through the AC List message element.
This feature must be disabled when the AC is behind a NAT and the IP
Address that is embedded would be invalid.
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The CAPWAP protocol has a feature that allows an AC to configure a
static IP address on a WTP. The WTP Static IP Address Information
message element provides such a function, however this feature SHOULD
NOT be used in NAT'ed environments, unless the administrator is
familiar with the internal IP addressing scheme within the WTP's
private network, and does not rely on the public address seen by the
AC.
When a WTP detects the duplicate address condition, it generates a
message to the AC, which includes the Duplicate IP Address message
element. The IP Address embedded within this message element is
different from the public IP address seen by the AC.
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13. Security Considerations
This section describes security considerations for the CAPWAP
protocol. It also provides security recommendations for protocols
used in conjunction with CAPWAP.
13.1. CAPWAP Security
As it is currently specified, the CAPWAP protocol sits between the
security mechanisms specified by the wireless link layer protocol
(e.g.IEEE 802.11i) and AAA. One goal of CAPWAP is to bootstrap trust
between the STA and WTP using a series of preestablished trust
relationships:
STA WTP AC AAA
==============================================
DTLS Cred AAA Cred
<------------><------------->
EAP Credential
<------------------------------------------>
wireless link layer
(e.g.802.11 PTK)
<-------------->
(derived)
Within CAPWAP, DTLS is used to secure the link between the WTP and
AC. In addition to securing control messages, it's also a link in
this chain of trust for establishing link layer keys. Consequently,
much rests on the security of DTLS.
In some CAPWAP deployment scenarios, there are two channels between
the WTP and AC: the control channel, carrying CAPWAP control
messages, and the data channel, over which client data packets are
tunneled between the AC and WTP. Typically, the control channel is
secured by DTLS, while the data channel is not. In the remote WTP
with local MAC deployment scenario, there is only one channel (a
control channel) between the AC and WTP.
The use of parallel protected and unprotected channels deserves
special consideration, but does not create a threat. There are two
potential concerns: attempting to convert protected data into un-
protected data and attempting to convert un-protected data into
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protected data. These concerns are addressed below.
13.1.1. Converting Protected Data into Unprotected Data
Since CAPWAP does not support authentication-only ciphers (i.e. all
supported ciphersuites include encryption and authentication), it is
not possible to convert protected data into unprotected data. Since
encrypted data is (ideally) indistinguishable from random data, the
probability of an encrypted packet passing for a well-formed packet
is effectively zero.
13.1.2. Converting Unprotected Data into Protected Data (Insertion)
The use of message authentication makes it impossible for the
attacker to forge protected records. This makes conversion of
unprotected records to protected records impossible.
13.1.3. Deletion of Protected Records
An attacker could remove protected records from the stream, though
not undetectably so, due the built-in reliability of the underlying
CAPWAP protocol. In the worst case, the attacker would remove the
same record repeatedly, resulting in a CAPWAP session timeout and
restart. This is effectively a DoS attack, and could be accomplished
by a man in the middle regardless of the CAPWAP protocol security
mechanisms chosen.
13.1.4. Insertion of Unprotected Records
An attacker could inject packets into the unprotected channel, but
this may become evident if sequence number desynchronization occurs
as a result. Only if the attacker is a MiM can packets be inserted
undetectably. This is a consequence of that channel's lack of
protection, and not a new threat resulting from the CAPWAP security
mechanism.
13.2. Use of Preshared Keys in CAPWAP
While use of preshared keys may provide deployment and provisioning
advantages not found in public key based deployments, it also
introduces a number of operational and security concerns. In
particular, because the keys must typically be entered manually, it
is common for people to base them on memorable words or phrases.
These are referred to as "low entropy passwords/passphrases".
Use of low-entropy preshared keys, coupled with the fact that the
keys are often not frequently updated, tends to significantly
increase exposure. For these reasons, we make the following
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recommendations:
o When DTLS is used with a preshared-key (PSK) ciphersuite, each WTP
SHOULD have a unique PSK. Since WTPs will likely be widely
deployed, their physical security is not guaranteed. If PSKs are
not unique for each WTP, key reuse would allow the compromise of
one WTP to result in the compromise of others
o Generating PSKs from low entropy passwords is NOT RECOMMENDED.
o It is RECOMMENDED that implementations that allow the
administrator to manually configure the PSK also provide a
capability for generation of new random PSKs, taking "RFC 1750
[4]" into account.
o Preshared keys SHOULD be periodically updated. Implementations
may facilitate this by providing an administrative interface for
automatic key generation and periodic update, or it may be
accomplished manually instead.
13.3. Use of Certificates in CAPWAP
For public-key-based DTLS deployments, each device SHOULD have unique
credentials, with a certificate profile authorizing them to act as
either a WTP or AC. If devices do not have unique credentials, it is
possible that by compromising one, any other one using the same
credential may also be considered to be compromised.
Each device is responsible for authenticating and authorizing devices
with which they communicate. At minimum, such authentication entails
validation of the chain of trust leading to the peer certificate,
followed by the the peer certificate itself. Implementations SHOULD
also provide a secure method for verifying that the credential in
question has not been revoked.
Note that if the WTP relies on the AC for network connectivity (e.g.
the AC is a layer 2 switch to which the WTP is directly connected),
there is a chicken and egg problem, in that the WTP may not be able
to contact an OCSP server or otherwise obtain an up to date CRL if a
compromised AC doesn't explicitly permit this. This cannot be
avoided, except through effective physical security and monitoring
measures at the AC.
13.4. AAA Security
The AAA protocol is used to distribute EAP keys to the ACs, and
consequently its security is important to the overall system
security. When used with TLS or IPsec, security guidelines specified
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in "RFC 3539 [12]" SHOULD be followed.
In general, the link between the AC and AAA server SHOULD be secured
using a strong ciphersuite keyed with mutually authenticated session
keys. Implementations SHOULD NOT rely solely on Basic RADIUS shared
secret authentication as it is often vulnerable to dictionary
attacks, but rather SHOULD use stronger underlying security
mechanisms.
13.5. IEEE 802.11 Security
When used with an IEEE 802.11 infrastructure with WEP encryption, the
CAPWAP protocol does not add any new vulnerabilities. Derived
session keys between the STA and WTP can be compromised, resulting in
many well-documented attacks. Implementors SHOULD discourage the use
of WEP and encourage use of technically sound cryptographic solutions
such as those in an IEEE 802.11 RSN.
STA authentication in CAPWAP is performed using IEEE 802.lX, and
consequently EAP. Implementors SHOULD use EAP methods meeting the
requirements specified in RFC 4017 [ref]
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14. IANA Considerations
A separate UDP port for data channel communications is (currently)
the selected demultiplexing mechanism, and a port must be assigned
for this purpose.
The Message element type fields must be IANA aassigned, see
Section 4.4.
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15. References
15.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001,
<http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.
[3] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-
MAC (CCM)", RFC 3610, September 2003.
[4] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
[5] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[6] "Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area networks
- Specific requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications",
IEEE Standard 802.11, 1999,
<http://standards.ieee.org/getieee802/download/
802.11-1999.pdf>.
[7] "Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area networks
- Specific requirements - Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications Amendment
6: Medium Access Control (MAC) Security Enhancements",
IEEE Standard 802.11i, July 2004, <http://standards.ieee.org/
getieee802/download/802.11i-2004.pdf>.
[8] Clark, D., "IP datagram reassembly algorithms", RFC 815,
July 1982.
[9] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES)
Key Wrap Algorithm", RFC 3394, September 2002.
[10] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation", RFC 1305, March 1992.
[11] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
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[12] Aboba, B. and J. Wood, "Authentication, Authorization and
Accounting (AAA) Transport Profile", RFC 3539, June 2003.
[13] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites for
Transport Layer Security (TLS)", RFC 4279, December 2005.
[14] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.1", RFC 4346, April 2006.
[15] "Netscape Certificate Extensions Specification",
<http://wp.netscape.com/eng/security/comm4-cert-exts.html>.
[16] Clancy, C., "Security Review of the Light Weight Access Point
Protocol", May 2005,
<http://www.cs.umd.edu/~clancy/docs/lwapp-review.pdf>.
[17] Rescorla et al, E., "Datagram Transport Layer Security",
June 2004.
[18] "Recommendation for Block Cipher Modes of Operation: the CMAC
Mode for Authentication", May 2005, <http://csrc.ncsl.nist.gov/
publications/nistpubs/800-38B/SP_800-38B.pdf>.
15.2. Informational References
[19] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
line Database", RFC 3232, January 2002.
[20] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
[21] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[22] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[23] Karn, P. and W. Simpson, "ICMP Security Failures Messages",
RFC 2521, March 1999.
[24] "WiFi Protected Access (WPA) rev 1.6", April 2003.
[25] Dierks et al, T., "The TLS Protocol Version 1.1", June 2005.
[26] Modadugu et al, N., "The Design and Implementation of Datagram
TLS", Feb 2004.
[27] "The Care and Feeding of Cookie Monsters", May 2006.
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[28] "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-17.txt", September 2004.
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Editors' Addresses
Pat R. Calhoun
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-853-5269
Email: pcalhoun@cisco.com
Michael P. Montemurro
Chantry Networks
1900 Minnesota Court, Suite 125
Mississauga, ON L5N 3C9
Canada
Phone: +1 905-363-6400
Email: montemurro.michael@gmail.com
Dorothy Stanley
Aruba Networks
1322 Crossman Ave
Sunnyvale, CA 94089
Phone: +1 630-363-1389
Email: dstanley@arubanetworks.com
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