Network Working Group                                 P. Calhoun, Editor
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Informational                     M. Montemurro, Editor
Expires: April 16, 2007                               Research In Motion
                                                      D. Stanley, Editor
                                                          Aruba Networks
                                                        October 13, 2006


                     CAPWAP Protocol Specification
              draft-ietf-capwap-protocol-specification-03

Status of this Memo

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   This Internet-Draft will expire on April 16, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).











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Abstract

   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.  The CAPWAP protocol binding which defines extensions for
   use with the IEEE 802.11 wireless LAN protocol is available in [11].
   Extensions are expected to be defined to enable use of the CAPWAP
   protocol with additional wireless technologies.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.1.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.2.  Conventions used in this document . . . . . . . . . . . .   7
     1.3.  Contributing Authors  . . . . . . . . . . . . . . . . . .   8
     1.4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . .   9
     1.5.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   9
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  10
     2.1.  Wireless Binding Definition . . . . . . . . . . . . . . .  11
     2.2.  CAPWAP Session Establishment Overview . . . . . . . . . .  11
     2.3.  CAPWAP State Machine Definition . . . . . . . . . . . . .  13
       2.3.1.  CAPWAP Protocol State Transitions . . . . . . . . . .  15
       2.3.2.  CAPWAP to DTLS Commands . . . . . . . . . . . . . . .  21
       2.3.3.  DTLS to CAPWAP Notifications  . . . . . . . . . . . .  21
       2.3.4.  DTLS State Transitions  . . . . . . . . . . . . . . .  22
     2.4.  Use of DTLS in the CAPWAP Protocol  . . . . . . . . . . .  25
       2.4.1.  DTLS Handshake Processing . . . . . . . . . . . . . .  26
       2.4.2.  DTLS Error Handling . . . . . . . . . . . . . . . . .  27
       2.4.3.  DTLS Rehandshake Behavior . . . . . . . . . . . . . .  28
       2.4.4.  DTLS EndPoint Authentication  . . . . . . . . . . . .  31
   3.  CAPWAP Transport  . . . . . . . . . . . . . . . . . . . . . .  34
     3.1.  UDP Transport . . . . . . . . . . . . . . . . . . . . . .  34
     3.2.  AC Discovery  . . . . . . . . . . . . . . . . . . . . . .  34
     3.3.  Fragmentation/Reassembly  . . . . . . . . . . . . . . . .  35
   4.  CAPWAP Packet Formats . . . . . . . . . . . . . . . . . . . .  36
     4.1.  CAPWAP Header . . . . . . . . . . . . . . . . . . . . . .  37
     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 . . . . . . . . . . . . . . . . . . . .  47
       4.4.2.  AC IPv4 List  . . . . . . . . . . . . . . . . . . . .  48
       4.4.3.  AC IPv6 List  . . . . . . . . . . . . . . . . . . . .  49



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       4.4.4.  AC Name . . . . . . . . . . . . . . . . . . . . . . .  49
       4.4.5.  AC Name with Index  . . . . . . . . . . . . . . . . .  50
       4.4.6.  AC Timestamp  . . . . . . . . . . . . . . . . . . . .  50
       4.4.7.  Add MAC ACL Entry . . . . . . . . . . . . . . . . . .  50
       4.4.8.  Add Station . . . . . . . . . . . . . . . . . . . . .  51
       4.4.9.  Add Static MAC ACL Entry  . . . . . . . . . . . . . .  52
       4.4.10. CAPWAP Control IPv4 Address . . . . . . . . . . . . .  52
       4.4.11. CAPWAP Control IPv6 Address . . . . . . . . . . . . .  53
       4.4.12. CAPWAP Timers . . . . . . . . . . . . . . . . . . . .  54
       4.4.13. Data Transfer Data  . . . . . . . . . . . . . . . . .  54
       4.4.14. Data Transfer Mode  . . . . . . . . . . . . . . . . .  55
       4.4.15. Decryption Error Report . . . . . . . . . . . . . . .  55
       4.4.16. Decryption Error Report Period  . . . . . . . . . . .  56
       4.4.17. Delete MAC ACL Entry  . . . . . . . . . . . . . . . .  56
       4.4.18. Delete Station  . . . . . . . . . . . . . . . . . . .  57
       4.4.19. Delete Static MAC ACL Entry . . . . . . . . . . . . .  57
       4.4.20. Discovery Type  . . . . . . . . . . . . . . . . . . .  58
       4.4.21. Duplicate IPv4 Address  . . . . . . . . . . . . . . .  58
       4.4.22. Duplicate IPv6 Address  . . . . . . . . . . . . . . .  59
       4.4.23. Idle Timeout  . . . . . . . . . . . . . . . . . . . .  60
       4.4.24. Image Data  . . . . . . . . . . . . . . . . . . . . .  60
       4.4.25. Image Filename  . . . . . . . . . . . . . . . . . . .  61
       4.4.26. Initiate Download . . . . . . . . . . . . . . . . . .  61
       4.4.27. Location Data . . . . . . . . . . . . . . . . . . . .  62
       4.4.28. MTU Discovery Padding . . . . . . . . . . . . . . . .  62
       4.4.29. Radio Administrative State  . . . . . . . . . . . . .  62
       4.4.30. Radio Operational State . . . . . . . . . . . . . . .  63
       4.4.31. Result Code . . . . . . . . . . . . . . . . . . . . .  64
       4.4.32. Session ID  . . . . . . . . . . . . . . . . . . . . .  65
       4.4.33. Statistics Timer  . . . . . . . . . . . . . . . . . .  65
       4.4.34. Vendor Specific Payload . . . . . . . . . . . . . . .  66
       4.4.35. WTP Board Data  . . . . . . . . . . . . . . . . . . .  66
       4.4.36. WTP Descriptor  . . . . . . . . . . . . . . . . . . .  67
       4.4.37. WTP Fallback  . . . . . . . . . . . . . . . . . . . .  69
       4.4.38. WTP Frame Tunnel Mode . . . . . . . . . . . . . . . .  70
       4.4.39. WTP IPv4 IP Address . . . . . . . . . . . . . . . . .  71
       4.4.40. WTP MAC Type  . . . . . . . . . . . . . . . . . . . .  71
       4.4.41. WTP Name  . . . . . . . . . . . . . . . . . . . . . .  72
       4.4.42. WTP Operational Statistics  . . . . . . . . . . . . .  72
       4.4.43. WTP Radio Statistics  . . . . . . . . . . . . . . . .  73
       4.4.44. WTP Reboot Statistics . . . . . . . . . . . . . . . .  74
       4.4.45. WTP Static IP Address Information . . . . . . . . . .  75
     4.5.  CAPWAP Protocol Timers  . . . . . . . . . . . . . . . . .  76
       4.5.1.  DiscoveryInterval . . . . . . . . . . . . . . . . . .  76
       4.5.2.  DTLSRehandshake . . . . . . . . . . . . . . . . . . .  76
       4.5.3.  DTLSSessionDelete . . . . . . . . . . . . . . . . . .  77
       4.5.4.  EchoInterval  . . . . . . . . . . . . . . . . . . . .  77
       4.5.5.  KeyLifetime . . . . . . . . . . . . . . . . . . . . .  77



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       4.5.6.  MaxDiscoveryInterval  . . . . . . . . . . . . . . . .  77
       4.5.7.  NeighborDeadInterval  . . . . . . . . . . . . . . . .  77
       4.5.8.  ResponseTimeout . . . . . . . . . . . . . . . . . . .  77
       4.5.9.  RetransmitInterval  . . . . . . . . . . . . . . . . .  78
       4.5.10. SilentInterval  . . . . . . . . . . . . . . . . . . .  78
       4.5.11. WaitJoin  . . . . . . . . . . . . . . . . . . . . . .  78
     4.6.  CAPWAP Protocol Variables . . . . . . . . . . . . . . . .  78
       4.6.1.  AdminState  . . . . . . . . . . . . . . . . . . . . .  78
       4.6.2.  DiscoveryCount  . . . . . . . . . . . . . . . . . . .  78
       4.6.3.  IdleTimeout . . . . . . . . . . . . . . . . . . . . .  78
       4.6.4.  MaxDiscoveries  . . . . . . . . . . . . . . . . . . .  78
       4.6.5.  MaxRetransmit . . . . . . . . . . . . . . . . . . . .  79
       4.6.6.  ReportInterval  . . . . . . . . . . . . . . . . . . .  79
       4.6.7.  RetransmitCount . . . . . . . . . . . . . . . . . . .  79
       4.6.8.  StatisticsTimer . . . . . . . . . . . . . . . . . . .  79
       4.6.9.  WTPFallBack . . . . . . . . . . . . . . . . . . . . .  79
     4.7.  WTP Saved Variables . . . . . . . . . . . . . . . . . . .  79
       4.7.1.  AdminRebootCount  . . . . . . . . . . . . . . . . . .  79
       4.7.2.  FrameEncapType  . . . . . . . . . . . . . . . . . . .  79
       4.7.3.  LastRebootReason  . . . . . . . . . . . . . . . . . .  79
       4.7.4.  MacType . . . . . . . . . . . . . . . . . . . . . . .  80
       4.7.5.  PreferredACs  . . . . . . . . . . . . . . . . . . . .  80
       4.7.6.  RebootCount . . . . . . . . . . . . . . . . . . . . .  80
       4.7.7.  Static ACL Table  . . . . . . . . . . . . . . . . . .  80
       4.7.8.  Static IP Address . . . . . . . . . . . . . . . . . .  80
       4.7.9.  WTPLinkFailureCount . . . . . . . . . . . . . . . . .  80
       4.7.10. WTPLocation . . . . . . . . . . . . . . . . . . . . .  80
       4.7.11. WTPName . . . . . . . . . . . . . . . . . . . . . . .  80
   5.  CAPWAP Discovery Operations . . . . . . . . . . . . . . . . .  81
     5.1.  Discovery Request Message . . . . . . . . . . . . . . . .  81
     5.2.  Discovery Response Message  . . . . . . . . . . . . . . .  82
     5.3.  Primary Discovery Request Message . . . . . . . . . . . .  82
     5.4.  Primary Discovery Response  . . . . . . . . . . . . . . .  83
   6.  CAPWAP Join Operations  . . . . . . . . . . . . . . . . . . .  84
     6.1.  Join Request  . . . . . . . . . . . . . . . . . . . . . .  84
     6.2.  Join Response . . . . . . . . . . . . . . . . . . . . . .  84
   7.  Control Channel Management  . . . . . . . . . . . . . . . . .  86
     7.1.  Echo Request  . . . . . . . . . . . . . . . . . . . . . .  86
     7.2.  Echo Response . . . . . . . . . . . . . . . . . . . . . .  86
   8.  WTP Configuration Management  . . . . . . . . . . . . . . . .  87
     8.1.  Configuration Consistency . . . . . . . . . . . . . . . .  87
       8.1.1.  Configuration Flexibility . . . . . . . . . . . . . .  88
     8.2.  Configuration Status  . . . . . . . . . . . . . . . . . .  88
     8.3.  Configuration Status Response . . . . . . . . . . . . . .  89
     8.4.  Configuration Update Request  . . . . . . . . . . . . . .  89
     8.5.  Configuration Update Response . . . . . . . . . . . . . .  90
     8.6.  Change State Event Request  . . . . . . . . . . . . . . .  91
     8.7.  Change State Event Response . . . . . . . . . . . . . . .  91



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     8.8.  Clear Configuration Request . . . . . . . . . . . . . . .  91
     8.9.  Clear Configuration Response  . . . . . . . . . . . . . .  92
   9.  Device Management Operations  . . . . . . . . . . . . . . . .  93
     9.1.  Image Data Request  . . . . . . . . . . . . . . . . . . .  93
     9.2.  Image Data Response . . . . . . . . . . . . . . . . . . .  94
     9.3.  Reset Request . . . . . . . . . . . . . . . . . . . . . .  94
     9.4.  Reset Response  . . . . . . . . . . . . . . . . . . . . .  94
     9.5.  WTP Event Request . . . . . . . . . . . . . . . . . . . .  95
     9.6.  WTP Event Response  . . . . . . . . . . . . . . . . . . .  95
     9.7.  Data Transfer Request . . . . . . . . . . . . . . . . . .  95
     9.8.  Data Transfer Response  . . . . . . . . . . . . . . . . .  96
   10. Station Session Management  . . . . . . . . . . . . . . . . .  97
     10.1. Station Configuration Request . . . . . . . . . . . . . .  97
     10.2. Station Configuration Response  . . . . . . . . . . . . .  97
   11. NAT Considerations  . . . . . . . . . . . . . . . . . . . . .  98
   12. Security Considerations . . . . . . . . . . . . . . . . . . . 100
     12.1. CAPWAP Security . . . . . . . . . . . . . . . . . . . . . 100
       12.1.1. Converting Protected Data into Unprotected Data . . . 101
       12.1.2. Converting Unprotected Data into Protected Data
               (Insertion) . . . . . . . . . . . . . . . . . . . . . 101
       12.1.3. Deletion of Protected Records . . . . . . . . . . . . 101
       12.1.4. Insertion of Unprotected Records  . . . . . . . . . . 101
     12.2. Use of Preshared Keys in CAPWAP . . . . . . . . . . . . . 101
     12.3. Use of Certificates in CAPWAP . . . . . . . . . . . . . . 102
     12.4. AAA Security  . . . . . . . . . . . . . . . . . . . . . . 103
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 104
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . . 105
     14.1. Normative References  . . . . . . . . . . . . . . . . . . 105
     14.2. Informational References  . . . . . . . . . . . . . . . . 105
   Editors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 106
   Intellectual Property and Copyright Statements  . . . . . . . . . 107




















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1.  Introduction

   This document describes the CAPWAP Protocol, a standard,
   interoperable protocol which enables an Access Controller (AC) to
   manage a collection of Wireless Termination Points (WTPs).  The
   CAPWAP protocol is defined to be independent of layer 2 technology.

   The emergence of centralized IEEE 802.11 Wireless Local Area Network
   (WLAN) architectures, in which simple IEEE 802.11 WTPs are managed by
   an Access Controller (AC) suggested 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).  An IEEE 802.11 binding is defined in [11] to support use
   of the CAPWAP protocol with IEEE 802.11 WLAN 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 CAPWAP
   protocol supports two modes of operation: Split and Local MAC.  In
   Split MAC mode all L2 wireless data and management frames are
   encapsulated via the CAPWAP protocol and exchanged between the AC and
   the WTP.  As shown in Figure 1, the wireless frames received from a
   mobile device, which is referred to in this specification as a
   Station (or STA for short), are directly encapsulated by the WTP and
   forwarded to the AC.

              +-+         wireless frames        +-+
              | |--------------------------------| |
              | |              +-+               | |
              | |--------------| |---------------| |
              | |wireless PHY/ | |     CAPWAP    | |
              | | MAC sublayer | |               | |
              +-+              +-+               +-+
              STA              WTP                AC

        Figure 1: Representative CAPWAP Architecture for Split MAC

   The Local MAC mode of operation allows for the data frames to be
   either locally bridged, or tunneled as 802.3 frames.  The latter
   implies that the WTP performs the 802 bridging function.  In either
   case the L2 wireless management frames are processed locally by the
   WTP, and then forwarded to the AC.  Figure 2 shows the Local MAC
   mode, in which a station transmits a wireless frame which is
   encapsulated in an 802.3 frame and forwarded to the AC.



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              +-+wireless frames +-+ 802.3 frames +-+
              | |----------------| |--------------| |
              | |                | |              | |
              | |----------------| |--------------| |
              | |wireless PHY/   | |     CAPWAP   | |
              | | MAC sublayer   | |              | |
              +-+                +-+              +-+
              STA                WTP               AC

        Figure 2: Representative CAPWAP Architecture for Local 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:

   1. To centralize the authentication and policy enforcement functions
      for a wireless network.  The AC may also provide centralized
      bridging, forwarding, and 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 many 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 station 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].



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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 a future revision 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:

   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:




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   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


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 [9].

1.5.  Terminology

   Access Controller (AC): The network entity that provides WTP access
   to the network infrastructure in the data plane, control plane,
   management plane, or a combination therein.

   Station (STA): A device that contains an IEEE 802.11 conformant
   medium access control (MAC) and physical layer (PHY) interface to the
   wireless medium (WM).

   Wireless Termination Point (WTP): The physical or network entity that
   contains an RF antenna and wireless PHY to transmit and receive
   station traffic for wireless access networks.

   This Document uses additional terminology defined in [8].

















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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)
   [7].  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 encapsulate 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.  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 stations that are communicating with
   the WTP.  This may include the creation of local data structures in
   the WTP for the stations and the collection of statistical
   information about the communication between the WTP and the stations.
   The CAPWAP protocol provides a mechanism for the AC to obtain
   statistical information collected by the WTP.



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   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.

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.

   When defining a binding for 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, a message element carried in the Station Configure Request
   to configure STA information on the WTP, and a WTP Radio Information
   message element carried in the Discovery Request, Primary Discovery
   Request and and Join Request messages, indicating the binding
   specific radio types supported at the WTP.  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 [11], 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 ------------]

            Discover Request     ------>
                                 <------       Discover Response

            [----------- end optional discovery ------------]



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                        (--- 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

                                   :
                                   :

           EventRequest          ------->



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                                 <------       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 3: 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.







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2.3.1.  CAPWAP Protocol State Transitions

   The following text discusses the various state transitions, and the
   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
         compatible, 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 compatible,
         the WTP will immediately transition to Image Data state (see
         transition (i)).  If the AC determines that a new firmware
         image should be installed on the WTP, the AC initiates a
         firmware download by sending an Image Data Request Message with
         an Initiate Download message element to the WTP

      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.






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      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.

      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).






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   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:

         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 Request:  The WTP receives a Clear Configuration
            Request 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).

         Station Configuration Request:  The WTP receives a Station
            Config Request message (see Section 10.1), to which it MUST
            respond with a Station 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 Response:  The AC receives a Clear Configuration
            Response message (see Section 8.9).

         Station Config:  The AC sends a Station Configuration Request
            message (see Section 10.1) or receives the corresponding
            Station Configuration 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 DTLSShutdown
         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.

   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.







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      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.

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



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   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.

   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.




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      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.

    Authenticate/Authorize to Shutdown (V)  This state transition
      indicates a failure of the DTLS handshake.







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      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.

      AC:  This state transition occurs when CAPWAP state machine sends
         a DTLSShutdown command, or when the WTP terminates the DTLS
         session.




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    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
   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.




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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.

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



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   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.

   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



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   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.

   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



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   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
   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.



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   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 [13].  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

   o  TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA




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   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, [6] defines several different methods for authenticating
   with preshared keys, and we focus on the following two:

   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).

   The first approach (plain PSK) is susceptible to passive dictionary
   attacks; hence, while this alorithm MUST 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.

   The following cryptographic algorithms MUST be supported when using
   preshared keys:

   o  TLS_PSK_WITH_AES_128_CBC_SHA

   o  TLS_PSK_WITH_3DES_EDE_CBC_SHA

   o  TLS_DHE_PSK_WITH_AES_128_CBC_SHA

   o  TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA

   The following algorithms MAY be supported when using preshared keys:

   o  TLS_PSK_WITH_AES_256_CBC_SHA

   o  TLS_DHE_PSK_WITH_AES_256_CBC_SHA








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2.4.4.3.  Certificate Usage

   When using certificates, both authentication and authorization must
   be considered.  Section 12.3 provides recommendations on how to
   authenticate a certificate and bind that to a CAPWAP entity.  This
   section deals with certificate authorization.

   Certificate authorization 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.509 certificates MUST include the
   Extended Key Usage (EKU)certificate extension [4].

   The EKU field indicates one or more purposes for which a certificate
   may be used.  It is an essential part in authorization.  Its syntax
   is as follows:

              ExtKeyUsageSyntax  ::=  SEQUENCE SIZE (1..MAX) OF KeyPurposeId

              KeyPurposeId  ::=  OBJECT IDENTIFIER


   Here we define two KeyPurposeId values, one for the WTP and one for
   the AC.  Inclusion of one of those two values indicates a certificate
   is authorized for use by a WTP or AC, respectively.  These values are
   formatted as id-kp fields.

             id-kp  OBJECT IDENTIFIER  ::=
                 { iso(1) identified-organization(3) dod(6) internet(1)
                   security(5) mechanisms(5) pkix(7) 3 }

              id-kp-capwapWTP  OBJECT IDENTIFIER  ::=  { id-kp 19 }

              id-kp-capwapAC   OBJECT IDENTIFIER  ::=  { id-kp 18 }

   For an AC, the id-kp-capwapAC EKU MUST be present in the certificate.
   For a WTP, the id-kp-capwapWTP EKU MUST be present in the
   certificate.

   Part of the CAPWAP certificate validation process includes ensuring
   that the proper EKU is included and only allowing the CAPWAP session
   to be established if the extension properly represents the device.







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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 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.

   Note that the optional fields defined in this section MUST be present
   in the precise order shown below.

        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   |  WBID   |T|F|L|W|M|     Flags     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Fragment ID          |     Frag Offset         |Rsvd |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 (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:  A 5 bit field containing the length of the CAPWAP transport
      header in 4 byte words (Similar to IP header length).  This length
      includes the optional headers.






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   WBID:  A 5 bit field which is the wireless binding identifier.  The
      identifier will indicate the type of wireless packet type
      associated with the radio.  The following values are defined:

      1 -  IEEE 802.11

      2 -  IEEE 802.16

      3 -  EPCGlobal

   T: The Type 'T' bit indicates the format of the frame being
      transported in the payload.  When this bit is set to one (1), the
      payload has the native frame format indicated by the WBID field.
      When this bit is zero (0) the payload is an IEEE 802.3 frame.

   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.

   L: The 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
      the last fragment.  When this bit is 0, the packet is not 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 this protocol MUST set to zero
      any bits that are reserved in the version of the protocol
      supported by that implementation.  Receivers MUST ignore all bits
      not defined for the version of the protocol they support.

   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.



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   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.
      Note the CAPWAP protocol does not allow for overlapping fragments.
      For instance, fragment 0 would include offset 0 with a payload
      length of 1000, while fragment 1 include offset 900 with a payload
      length of 600.

   Reserved:  The 3-bit field is reserved for future use.  All
      implementations complying with this protocol MUST set to zero any
      bits that are reserved in the version of the protocol supported by
      that implementation.  Receivers MUST ignore all bits not defined
      for the version of the protocol they support.

   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.  Given the HLEN field assumes 4 byte alignment,
      this field MUST be padded with zeroes (0x00) if it is not 4 byte
      aligned.

      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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Length:  The number of bytes in the MAC Address field.  The length
         field is present since some technologies (e.g., IEEE 802.16)
         are now using 64 bit 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.  Given the HLEN field assumes 4 byte alignment,
      this field MUST be padded with zeroes (0x00) if it is not 4 byte
      aligned.

      The field contains the basic 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Wireless ID  |    Length     |             Data
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Wireless ID:  The wireless binding identifier.  The following
         values are defined:

         1 -  IEEE 802.11

         2 -  IEEE 802.16

         3 -  EPCGlobal

      Length:  The length of the data field

      Data:  Wireless specific information, defined by the wireless
         specific binding.

   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 encapsulates a forwarded wireless
   frame.  The CAPWAP protocol defines two different modes of
   encapsulation; 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
   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.



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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.

   Join:  CAPWAP Join messages are used to for a WTP to request service
      from an AC, and for the AC to respond to the WTP.

   Control Channel Management:  CAPWAP control channel management
      messages are used to maintain the control channel.

   WTP Configuration Management:  The WTP Configuration messages are
      used by the AC to push a specific configuration to the WTP.
      Messages which provide retrieval of statistics from the WTP also
      fall in this category.

   Station Session Management:  Station session management messages are
      used by the AC to push specific Station policies to the WTP.

   Device Management Operations:  Device management operations are used
      to request and deliver a firmware image to the WTP.

   Binding Specific CAPWAP Management Frames:  Messages in this category
      are used by the AC and the WTP to exchange protocol-specific
      CAPWAP management messages.  These messages may or may not be used
      to change the link state of a station.

   Discovery, Join, Control Message Management, WTP Configuration
   Management and Station Session Management CAPWAP control messages
   MUST be implemented.  Device Operations Management messages MAY be
   implemented.

   CAPWAP control messages sent from the WTP to the AC indicate that the
   WTP is operational, providing an implicit keep-alive mechanism for
   the WTP.  The Control Channel Management Echo Request and Echo
   Response messages provide an explicit keep-alive mechanism when other
   CAPWAP control messages are not exchanged.

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 an enterprise specific message type number.  The first
   three octets is the enterprise number in network byte order, with
   zero being used for CAPWAP generic message types and the IEEE 802.11
   IANA assigned enterprise number 13277 being used for IEEE 802.11
   technology specific message types.  The last octet is the enterprise
   specific message type number, which has a range from 0 to 255.  The
   message type field can be expressed as:

Message Type = IANA Enterprise Number * 256 + enterprise specific message type number

   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 Configuration Request         23
           Clear Configuration Response        24
           Station Configuration Request       25
           Station Configuration Response      26

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.






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4.3.1.4.  Flags

   The Flags field MUST be set to zero.

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 defined below.  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.

   Note that unless otherwise specified, a control message that lists a
   set of supported (or expected) message elements MUST not expect the
   message elements to be in any specific order.  The sender may order
   the message elements as convenient.  Furthermore, unless specifically
   noted, any individual message element may exist one or more times



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   within a given control message.

   Additional message elements may be defined in separate IETF
   documents.

   The format of a message element uses the TLV format shown here:

      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.  Type field values are allocated as
   follows:

              Usage                              Type Values

   CAPWAP Protocol Message Elements                1-1023
   IEEE 802.11 Message Elements                    1024-2047
   IEEE 802.16 Message Elements                    2048 - 3071
   EPCGlobal Message Elements                      3072 - 4095
   Reserved for Future Use                         4096 - 65024

   The table below lists the CAPWAP protocol Message Elements and their
   Type values.





















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   CAPWAP Message Element                            Type Value

   AC Descriptor                                         1
   AC IPv4 List                                          2
   AC IPv6 List                                          3
   AC Name                                               4
   AC Name with Index                                    5
   AC Timestamp                                          6
   Add MAC ACL Entry                                     7
   Add Station                                           8
   Add Static MAC ACL Entry                              9
   CAPWAP Control IPV4 Address                          10
   CAPWAP Control IPV6 Address                          11
   CAPWAP Timers                                        12
   Data Transfer Data                                   13
   Data Transfer Mode                                   14
   Decryption Error Report                              15
   Decryption Error Report Period                       16
   Delete MAC ACL Entry                                 17
   Delete Station                                       18
   Delete Static MAC ACL Entry                          19
   Discovery Type                                       20
   Duplicate IPv4 Address                               21
   Duplicate IPv6 Address                               22
   Idle Timeout                                         23
   Image Data                                           24
   Image Filename                                       25
   Initiate Download                                    26
   Location Data                                        27
   MTU Discovery Padding                                28
   Radio Administrative State                           29
   Radio Operational State                              30
   Result Code                                          31
   Session ID                                           32
   Statistics Timer                                     33
   Vendor Specific Payload                              34
   WTP Board Data                                       35
   WTP Descriptor                                       36
   WTP Fallback                                         37
   WTP Frame Tunnel Mode                                38
   WTP IPv4 IP Address                                  39
   WTP MAC Type                                         40
   WTP Name                                             41
   WTP Operational Statistics                           42
   WTP Radio Statistics                                 43
   WTP Reboot Statistics                                44
   WTP Static IP Address Information                    45




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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Stations           |             Limit             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Active WTPs          |            Max WTPs           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Security   |  R-MAC Field  |Wireless Field |   Reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=4                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=5                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   1 for AC Descriptor

   Length:   >= 12

   Stations:   The number of stations currently associated with the AC

   Limit:   The maximum number of stations supported by the AC

   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






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      2 -  Pre-Shared Secret

   R-MAC Field:   The AC supports the optional Radio MAC Address field
      in the CAPWAP transport Header (see Section 4.1).

   Wireless Field:   The AC supports the optional Wireless Specific
      Information field in the CAPWAP Header (see Section 4.1).

   Reserved:   All implementations complying with this protocol MUST set
      to zero any bits that are reserved in the version of the protocol
      supported by that implementation.  Receivers MUST ignore all bits
      not defined for the version of the protocol they support.

   Vendor Identifier:   A 32-bit value containing the IANA assigned "SMI
      Network Management Private Enterprise Codes"

   Type:   Vendor specific encoding of AC information.  The following
      values are supported.  The Hardware and Software Version values
      MUST be included.

      4 - Hardware Version:   The AC's hardware version number.

      5 - Software Version:   The AC's Firmware version number.

   Length:   Length of vendor specific encoding of AC information.

   Value:   Vendor specific encoding of AC information.

4.4.2.  AC IPv4 List

   The AC IPv4 List message element is used to configure a WTP with the
   latest list of ACs available for the WTP to join.


        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.





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4.4.3.  AC IPv6 List

   The AC IPv6 List message element is used to configure a WTP with the
   latest list of ACs available for the WTP to join.


        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[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   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 UTF-8 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 UTF-8 encoded string containing the AC's
      name







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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).

   AC Name:   A variable length UTF-8 encoded 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 [3].

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



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   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.

4.4.8.  Add Station

   The Add Station message element is used by the AC to inform a WTP
   that it should forward traffic for a particular station.  The Add
   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 station.

   Once a 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 Station message element.  When a WTP receives an Add
   Station message element for an existing station, it must override any
   existing state it may have for the station in question.  The latest
   Add 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 Station







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   Length:   >= 7

   Radio ID:   An 8-bit value representing the radio

   MAC Address:   The station's MAC Address

   VLAN Name:   An optional variable length UTF-8 encoded 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.

      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 Control IPv4 Address

   The CAPWAP 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 WTPs
   connected.  In the event that multiple CAPWAP Control IPV4 Address
   message elements are returned, the WTP is expected to perform load
   balancing across the multiple interfaces.








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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           WTP Count           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   10 for CAPWAP Control IPv4 Address

   Length:   6

   IP Address:   The IP Address of an interface.

   WTP Count:   The number of WTPs currently connected to the interface.

4.4.11.  CAPWAP Control IPv6 Address

   The CAPWAP 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:   11 for CAPWAP Control IPv6 Address

   Length:   18

   IP Address:   The IP Address of an interface.

   WTP Count:   The number of WTPs currently connected to the interface.






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4.4.12.  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:   12 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.  The default value for this message element can be found
      in Section 4.5.4.

4.4.13.  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:   13 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








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   Data Length:   Length of data field.

   Data:   Debug information.

4.4.14.  Data Transfer Mode

   The Data Transfer Mode message element is used by the WTP to indicate
   the type of data transfer information it is sending to the AC for
   debugging purposes.

      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |   Data  Type   |
     +-+-+-+-+-+-+-+-+

   Type:   14 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

4.4.15.  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 |      Station MAC Address      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                     Station MAC Address[]                     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   15 for Decryption Error Report

   Length:   >= 8






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   Radio ID:   The Radio Identifier, which typically refers to an
      interface index on the WTP

   Num Of Entries:   An 8-bit unsigned integer indicating the number of
      station MAC addresses.

   Station MAC Address:   An array of station MAC addresses that have
      caused decryption errors.

4.4.16.  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:   16 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.  The default value for this message element can be found
      in Section 4.6.6.

4.4.17.  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[]                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   Type:   17 for Delete 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 ACL.

4.4.18.  Delete Station

   The Delete Station message element is used by the AC to inform an WTP
   that it should no longer provide service to a particular station.
   The WTP must terminate service immediately upon receiving this
   message element.

   The transmission of a Delete Station message element could occur for
   various reasons, including for administrative reasons, as a result of
   the fact that the station has roamed to another WTP, etc.

      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:   18 for Delete Station

   Length:   7

   Radio ID:   An 8-bit value representing the radio

   MAC Address:   The station's MAC Address

4.4.19.  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:   19 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.

4.4.20.  Discovery Type

   The Discovery Type message element is used by the WTP to indicate how
   it has come to know about the existence of the AC, to which it is
   sending the Discovery Request message.

      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     | Discovery Type|
     +-+-+-+-+-+-+-+-+

   Type:   20 for Discovery Type

   Length:   1

   Discovery Type:   An 8-bit value indicating how the WTP discovered
      the AC .  The following values are supported:

      0 -  Unknown

      1 -  Static Configuration

      2 -  DHCP

      3 -  DNS

      4 -  AC Referral

4.4.21.  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.






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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          MAC Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          MAC Address          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   21 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.

4.4.22.  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:   22 for Duplicate IPv6 Address

   Length:   22

   IP Address:   The IP Address currently used by the WTP.






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   MAC Address:   The MAC Address of the offending device.

4.4.23.  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
   station entries.  The value applies for all radios 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Timeout                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   23 for Idle Timeout

   Length:   4

   Timeout:   The current idle timeout to be enforced by the WTP.  The
      default value for this message element can be found in
      Section 4.6.3.

4.4.24.  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:   24 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







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      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.

4.4.25.  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 UTF-8 encoded string, which is NOT zero
   terminated.

      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:   25 for Image Filename

   Length:   >= 1

   Filename:   A variable length UTF-8 encoded string containing the
      filename to download.

4.4.26.  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:   24 for Initiate Download

   Length:   0








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4.4.27.  Location Data

   The Location Data message element is a variable length byte UTF-8
   encoded 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:   27 for Location Data

   Length:   > 0

   Location:   A non-zero terminated UTF-8 encoded string containing the
      WTP location.

4.4.28.  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:   28 for MTU Discovery Padding

   Length:   variable

   Pad:   A variable length pad.

4.4.29.  Radio Administrative State

   The radio administrative state message element is used to communicate
   the state of a particular radio.  The configuration of the Radio
   Administrative State is sent by the AC to change the state of the
   WTP, which saves the value to ensure its effect remains across WTP
   resets.  The WTP communicates this message element during the
   configuration phase to ensure that AC has the WTP radio's current



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   administrative state settings.  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    |  Admin State  |     Cause     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   29 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 default value for the Admin State field is
      listed in section Section 4.6.1.  The following values are
      supported:

      1 -  Enabled

      2 -  Disabled

   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

      3 -  Radar Detection

4.4.30.  Radio Operational State

   The Radio Operational State message element is sent by the WTP to the
   AC to communicate a change in the operational state of a radio.  For
   instance, if the WTP were to detect that a hardware failure existed
   with a radio, which caused the radio to be taken offline, the WTP
   would indicate this event to the AC via the message element.  The AC
   MAY also send this message element to change the operational state of



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   a specific radio.  Note that the operational state setting is not
   saved on the WTP, and therefore does not remain across WTP resets.
   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     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   30 for Radio Operational State

   Length:   3

   Radio ID:   The Radio Identifier, typically refers to some interface
      index on the WTP.  A value of 0xFF is invalid, as it is not
      possible to change the WTP's operational state.

   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

      3 -  Administratively Set

4.4.31.  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                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






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   Type:   31 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)

      8  Failure (Join Failure, WTP Hardware not supported)

      9  Failure (Unable to Reset)

4.4.32.  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                                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   32 for Session ID

   Length:   4

   Session ID:   A 32-bit random session identifier

4.4.33.  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.



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      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Statistics Timer       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   33 for Statistics Timer

   Length:   2

   Statistics Timer:   A 16-bit unsigned integer indicating the time, in
      seconds.  The default value for this timer can be found in section
      Section 4.6.8.

4.4.34.  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:   34 for Vendor Specific

   Length:   >= 7

   Vendor Identifier:   A 32-bit value containing the IANA assigned "SMI
      Network Management Private Enterprise Codes" [12]

   Element ID:   A 16-bit Element Identifier which is managed by the
      vendor.

   Value:   The value associated with the vendor specific element.

4.4.35.  WTP Board Data

   The WTP Board Data message element is sent by the WTP to the AC and
   contains information about the hardware present.







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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=0                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=1                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Optional additional vendor specific WTP board data TLVs



   Type:   35 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.

      3 - Board Revision   A revision number of the board, which MAY be
         included in the WTP Board Data message element.

4.4.36.  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.








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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   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:   36 for WTP Descriptor

   Length:   >= 31

   Max Radios:   An 8-bit value representing the number of radios (where
      each radio is identified via the Radio ID, or 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.  A WTP that does not have
      any encryption capabilities sets this field to zero (0).  Refer to
      the specific wireless 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"







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   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:   The WTP's hardware version number.

      5 - Software Version:   The WTP's Firmware version number.

      6 - Boot Version:   The WTP's boot loader's version number.

   Length:   Length of vendor specific encoding of WTP information.

   Value:   Vendor specific data of WTP information encoded in the UTF-8
      format.

4.4.37.  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:   37 for WTP Fallback

   Length:   1

   Mode:   The 8-bit value indicates the status of automatic CAPWAP
      fallback on the WTP.  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



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      command).  The default value for this field can be found in
      section Section 4.6.9.  The following values are supported:

      1 -  Enabled

      2 -  Disabled

4.4.38.  WTP Frame Tunnel Mode

   The WTP Frame Tunnel Mode message element allows the WTP to
   communicate the 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
     +-+-+-+-+-+-+-+-+
     | Tunnel Mode   |
     +-+-+-+-+-+-+-+-+

   Type:   38 for WTP Frame Tunnel Mode

   Length:   1

   Frame Tunnel Mode:   The Frame Tunnel mode specifies the tunneling
      modes for station data which are supported by the WTP.  The
      following values are supported:

      1 - Local Bridging:   When Local Bridging is used, the WTP does
         not tunnel user traffic to the AC; all user traffic is locally
         bridged.  This value MUST NOT be used when the WTP MAC Type is
         set to Split-MAC.

      2 - 802.3 Frame Tunnel Mode:   The 802.3 Frame Tunnel Mode
         requires the WTP and AC to encapsulate all user payload as
         native IEEE 802.3 frames (see Section 4.2).  All user traffic
         is tunneled to the AC.  This value MUST NOT be used when the
         WTP MAC Type is set to Split-MAC.

      4 - Native Frame Tunnel Mode:   Native Frame Tunnel mode requires
         the WTP and AC to encapsulate all user payloads as native
         wireless frames, as defined by the wireless binding (see for
         example Section 4.2).

      7 - All:   The WTP is capable of supporting all frame tunnel
         modes.





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4.4.39.  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:   39 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.

4.4.40.  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:   40 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.

      2 - Both:   WTP is capable of supporting both Local-MAC and Split-
         MAC.






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4.4.41.  WTP Name

   The WTP Name message element is a variable length byte UTF-8 encoded
   string.  The string is not zero terminated.

      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+-
     | WTP Name ...
     +-+-+-+-+-+-+-+-+-

   Type:   41 for WTP Name

   Length:   variable

   WTP Name:   A non-zero terminated UTF-8 encoded string containing the
      WTP name.

4.4.42.  WTP Operational Statistics

   The WTP Operational Statistics message element is sent by the WTP to
   the AC to provide statistics related to the operation of 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID   | Tx Queue Level | Wireless Link Frames per Sec  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   42 for WTP Operational Statistics

   Length:   4

   Radio ID:   The radio ID of the radio to which the statistics apply.

   Wireless Transmit Queue Level:   The percentage of Wireless Transmit
      queue utilization, calaculated as the sum of utilized transmit
      queue lengths divided by the sum of maximum transmit queue
      lengths, multiplied by 100.  The Wireless Transmit Queue Level is
      representative of congestion conditions over wireless interfaces
      between the WTP and wireless terminals.

   Wireless Link Frames per Sec:   The number of frames transmitted or
      received per second by the WTP over the air interface.






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4.4.43.  WTP Radio Statistics

   The WTP Radio Statistics message element is sent by the WTP to the AC
   to communicate statistics on radio behavior and reasons why the WTP
   radio has been reset.

      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    | Last Fail Type|       Reset Count             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     SW Failure Count          |        HW Failure Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Other  Failure Count       |   Unknown Failure Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Config Update Count         |    Channel Change Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Band Change Count           |    Current Noise Floor        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   43 for WTP Radio Statistics

   Length:   20

   Radio ID:   The radio ID of the radio to which the statistics apply.

   Last Failure Type:   The last WTP failure.  The following values are
      supported:

      0 -  Statistic Not Supported

      1 -  Software Failure

      2 -  Hardware Failure

      3 -  Other Failure

      255 -  Unknown (e.g., WTP doesn't keep track of info)

   Reset Count:   The number of times that that the radio has been
      reset.

   SW Failure Count:   The number of times that the radio has failed due
      to software related reasons.







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   HW Failure Count:   The number of times that the radio has failed due
      to hardware related reasons.

   Other Failure Count:   The number of times that the radio has failed
      due to known reasons, other than software or hardware failure.

   Unknown Failure Count:   The number of times that the radio has
      failed for unknown reasons.

   Config Update Count:   The number of times that the radio
      configuration has been updated.

   Channel Change Count:   The number of times that the radio channel
      has been changed.

   Band Change Count:   The number of times that the radio has changed
      frequency bands.

   Current Noise Floor:   A signed integer which indicates the noise
      floor of the radio receiver in units of dBm.

4.4.44.  WTP Reboot Statistics

   The WTP Reboot Statistics message element is sent by the WTP to the
   AC to communicate reasons why WTP 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Reboot Count          |    AC Initiated Count         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Link Failure Count       |    SW Failure Count           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      HW Failure Count         |    Other Failure Count        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Unknown Failure Count    |Last Failure Type|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   44 for WTP Reboot Statistics

   Length:   15

   Reboot 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.





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   AC 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
      protocol reset request.  A value of 65535 implies that this
      information is not available on the WTP.

   Link Failure Count:   The number of times that a CAPWAP protocol
      connection with an AC has failed due to link failure.

   SW Failure Count:   The number of times that a CAPWAP protocol
      connection with an AC has failed due to software related reasons.

   HW Failure Count:   The number of times that a CAPWAP protocol
      connection with an AC has failed due to hardware related reasons.

   Other Failure Count:   The number of times that a CAPWAP protocol
      connection with an AC has failed due to known reasons, other than
      AC initiated, link, SW or HW failure.

   Unknown Failure Count:   The number of times that a CAPWAP protocol
      connection with an AC has failed for unknown reasons.

   Last Failure Type:   The failure type of the most recent WTP failure.
      The following values are supported:

      0 -  Not Supported

      1 -  AC Initiated (see Section 9.3)

      2 -  Link Failure

      3 -  Software Failure

      4 -  Hardware Failure

      5 -  Other Failure

      255 -  Unknown (e.g., WTP doesn't keep track of info)

4.4.45.  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.







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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Netmask                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Gateway                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Static     |
     +-+-+-+-+-+-+-+-+

   Type:   45 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.

   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.



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   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

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





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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

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, making explicit configuration unnecessary in
   many cases.  If the default values are explicitly overriden by the
   AC, the WTP MUST save the values sent by the AC.

4.6.1.  AdminState

   The default Administrative State value is enabled (1).

4.6.2.  DiscoveryCount

   The number of discoveries transmitted by a WTP to a single AC.  This
   is a monotonically increasing counter.

4.6.3.  IdleTimeout

   The default Idle Timeout is 300 seconds.

4.6.4.  MaxDiscoveries

   The maximum number of discovery requests that will be sent after a
   WTP boots.



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   Default: 10

4.6.5.  MaxRetransmit

   The maximum number of retransmissions for a given CAPWAP packet
   before the link layer considers the peer dead.

   Default: 5

4.6.6.  ReportInterval

   The default Report Interval is 120 seconds.

4.6.7.  RetransmitCount

   The number of retransmissions for a given CAPWAP packet.  This is a
   monotonically increasing counter.

4.6.8.  StatisticsTimer

   The default Statistics Interval is 120 seconds.

4.6.9.  WTPFallBack

   The default WTP Fallback value is enabled (1).

4.7.  WTP Saved Variables

   In addition to the values defined in Section 4.6, the following
   values SHOULD be saved on the WTP in non-volatile memory.  CAPWAP
   wireless bindings may define additional values that SHOULD be stored
   on the WTP.

4.7.1.  AdminRebootCount

   The number of times the WTP has rebooted administratively, defined in
   Section 4.4.44.

4.7.2.  FrameEncapType

   For WTPs that support multiple Frame Encapsulation Types, it is
   useful to save the value configured by the AC.  The Frame
   Encapsulation Type is defined in Section 4.4.38.

4.7.3.  LastRebootReason

   The reason why the WTP last rebooted, defined in Section 4.4.44.




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4.7.4.  MacType

   For WTPs that support multiple MAC Types, it is usefule to save the
   value configured by the AC.  The MAC Type is defined in
   Section 4.4.40.

4.7.5.  PreferredACs

   The preferred ACs, with the index, defined in Section 4.4.5.

4.7.6.  RebootCount

   The number of times the WTP has rebooted, defined in Section 4.4.44.

4.7.7.  Static ACL Table

   The static ACL table saved on the WTP, as configured by the Add
   Static MAC ACL Entry message element, see Section 4.4.9.

4.7.8.  Static IP Address

   The static IP Address assigned to the WTP, as configured by the
   message element, see Section 4.4.45.

4.7.9.  WTPLinkFailureCount

   The number of times the link to the AC has failed, see
   Section 4.4.44.

4.7.10.  WTPLocation

   The WTP Location, defined in Section 4.4.27.

4.7.11.  WTPName

   The WTP Name, defined in Section 4.4.41.















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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 4.4.20

   o  WTP Descriptor, see Section 4.4.36

   o  WTP Frame Tunnel Mode, see Section 4.4.38

   o  WTP MAC Type, see Section 4.4.40

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  CAPWAP Control IPv4 Address, see Section 4.4.10

   o  CAPWAP Control IPv6 Address, see Section 4.4.11

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
   state.




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   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 4.4.20

   o  WTP Descriptor, see Section 4.4.36

   o  WTP Frame Tunnel Mode, see Section 4.4.38

   o  WTP MAC Type, see Section 4.4.40

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  CAPWAP Control IPv4 Address, see Section 4.4.10

   o  CAPWAP Control IPv6 Address, see Section 4.4.11









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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 (optionally) 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.

   If the AC rejects the Join Request, it sends a Join Response message
   with a failure indication then enters the CAPWAP reset state,
   resulting in shutdown of the DTLS session.

   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 4.4.27

   o  Session ID, see Section 4.4.32

   o  WTP Descriptor, see Section 4.4.36

   o  WTP IPv4 IP Address, see Section 4.4.39

   o  WTP Name, see Section 4.4.41

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.




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   Upon receipt of the DTLSClientHello, 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 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  AC IPv4 List, see Section 4.4.2

   o  AC IPv6 List, see Section 4.4.3

   o  Result Code, see Section 4.4.31

   o  Session ID, see Section 4.4.32

   The following message element MUST be included in the Join Response
   message.

   o  AC Descriptor, see Section 4.4.1
















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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.  CAPWAP control messages,
   such as the WTP Event Request message sent from the WTP to the AC
   indicate to the AC that the WTP is operational.  When such control
   messages are not being sent, the Echo Request and Echo Response
   messages are used to maintain the 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 Radio
   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 4.4.29

   o  Statistics Timer, see Section 4.4.33

   o  WTP Board Data, see Section 4.4.35

   o  WTP Reboot Statistics, see Section 4.4.44




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   The following message elements MAY be included in the Configuration
   Status message.

   o  WTP Static IP Address Information, see Section 4.4.45

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 Radio Operational
   State 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 4.4.12

   o  Radio Operational Event, see Section 4.4.30

   o  Decryption Error Report Period, see Section 4.4.16

   o  Idle Timeout, see Section 4.4.23

   o  WTP Fallback, see Section 4.4.37

8.4.  Configuration Update Request

   Configuration 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.




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   When an AC receives a Configuration Update Request message it will
   respond with a Configuration Update Response message, with the
   appropriate Result Code.

   One or more of the following message elements MAY be included in the
   Configuration Update message.

   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 4.4.12

   o  Decryption Error Report Period, see Section 4.4.16

   o  Delete MAC ACL Entry, see Section 4.4.17

   o  Delete Static MAC ACL Entry, see Section 4.4.19

   o  Idle Timeout, see Section 4.4.23

   o  Location Data, see Section 4.4.27

   o  Radio Operational State, see Section 4.4.30

   o  Statistics Timer, see Section 4.4.33

   o  WTP Fallback, see Section 4.4.37

   o  WTP Name, see Section 4.4.41

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 Configuration Update Response message the
   result code indicates if the WTP successfully accepted the
   configuration.

   The following message element MUST be present in the Configuration



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   Update message.

   Result Code, see Section 4.4.31

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 one of the WTP radio's operational state.

   The Change State Event Request message MUST sent by the WTP when it
   receives a Configuration Response message that includes a Radio
   Operational State 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 Request 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  Radio Operational State message element, see Section 4.4.30

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 sent by an AC in response to
   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.

8.8.  Clear Configuration Request

   The Clear Configuration Request message is used to reset a WTP's
   configuration.

   The Clear Configuration Request message is sent by an AC to request
   that a WTP reset its configuration to the manufacturing default
   configuration.  The Clear Config Request message is sent while in the



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   Run CAPWAP state.

   The Clear Configuration Request message carries no message elements.

   When a WTP receives a Clear Configuration Request message it resets
   its configuration to the manufacturing default configuration.

8.9.  Clear Configuration Response

   The Clear Configuration Response message is sent by the WTP after
   receiving a Clear Configuration Request message and resetting its
   configuration parameters back to the manufacturing default values.

   The Clear Configuration Request message carries the message elements.

   o  Result Code, see Section 4.4.31



































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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 4.4.24

   o  Image Filename, see Section 4.4.25

   o  Initiate Download, see Section 4.4.26




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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 indicating success and then reinitialize itself.  In the
   event the WTP is unable to reset, including a hardware reset, it can
   respond with a Reset Response whose Result-Code message element
   indicates failure.

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 following message elements MAY be included in the Image Data
   Request Message.

   o  Result Code, see Section 4.4.31

   When an AC receives a successful Reset Response message, it is
   notified that the WTP will reinitialize its operation.  An AC that
   receives a Reset Response indicating failure may opt to no longer
   provide service to the WTP in question.







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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.

   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 4.4.15

   o  Duplicate IPv4 Address, see Section 4.4.21

   o  Duplicate IPv6 Address, see Section 4.4.22

   o  WTP Operational Statistics, see Section 4.4.42

   o  WTP Radio Statistics, see Section 4.4.43

   o  WTP Reboot Statistics, see Section 4.4.44

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.



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   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 Data, see Section 4.4.13

   o  Data Transfer Mode, see Section 4.4.14

9.8.  Data Transfer Response

   The Data Transfer Response message acknowledges the Data Transfer
   Request message.

   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.  Station Session Management

   Messages in this section are used by the AC to create, modify or
   delete station session state on the WTPs.

10.1.  Station Configuration Request

   The Station Configuration Request message is used to create, modify
   or delete station 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
   Station Configuration Request message.

   o  Add Station, see Section 4.4.8

   o  Delete Station, see Section 4.4.18

10.2.  Station Configuration Response

   The Station Configuration Response message is used to acknowledge a
   previously received Station Configuration Request message.  The
   following message element MUST be present in the Station
   Configuration Response message.

   o  Result Code, see Section 4.4.31

   The Result Code message element indicates that the requested
   configuration was successfully applied, or that an error related to
   processing of the Station Configuration Request message occurred on
   the WTP.
















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11.  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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12.  Security Considerations

   This section describes security considerations for the CAPWAP
   protocol.  It also provides security recommendations for protocols
   used in conjunction with CAPWAP.

12.1.  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 802.11) 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. IEEE 802.11 PTK)
          <--------------> or
          <--------------------------->
              (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.

   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
   protected data.  These concerns are addressed below.



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12.1.1.  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.

12.1.2.  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.

12.1.3.  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.

12.1.4.   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.

12.2.  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
   recommendations:




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   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 [2]
      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.

12.3.  Use of Certificates in CAPWAP

   For public-key-based DTLS deployments, each device SHOULD have unique
   credentials, with an extended key usage 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.

   Certificate validation involves checking a large variety of things.
   Since the necessary things to validate are often environment-
   specific, many are beyond the scope of this document.  In this
   section, we provide some basic guidance on certificate validation.

   Each device is responsible for authenticating and authorizing devices
   with which they communicate.  Authentication entails validation of
   the chain of trust leading to the peer certificate, followed by the
   the peer certificate itself.  At a minimum, devices SHOULD use SSH-
   style certificate caching to guarantee consistency.  If devices have
   access to a certificate authority, they SHOULD properly validate the
   trust chain.  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.




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   Proper validation of certificates typically requires checking to
   ensure the certificate has not yet expired.  If devices have a real-
   time clock, they SHOULD verify the certificate validity dates.  If no
   real-time clock is available, the device SHOULD make a best-effort
   attempt to validate the certificate validity dates through other
   means.  Failure to check a certificate's temporal validity can make a
   device vulnerable to man-in-the-middle attacks launched using
   compromised, expired certificates, and therefore devices should make
   every effort to perform this validation.

   Another important part of certificate authentication is binding a
   certificate to a particular device.  There are many ways to
   accomplish this.  Specificaiton of the certificate common name (CN)
   as the WTP or AC MAC address formatted as ASCII HEX, for example, 01:
   23:45:67:89:ab is REQUIRED for use with the CAPWAP protocol.  During
   authentication, devices SHOULD ensure that the MAC address matches
   the MAC address specified in the CAPWAP header.  If this mechanism is
   used, the ACs SHOULD maintain list of all authorized WTP MAC
   addresses and the WTP SHOULD save the AC credential or credential
   identifier.

12.4.  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
   in RFC 3539 [5] 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.

















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13.  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.














































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14.  References

14.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Eastlake, D., Crocker, S., and J. Schiller, "Randomness
         Recommendations for Security", RFC 1750, December 1994.

   [3]   Mills, D., "Network Time Protocol (Version 3) Specification,
         Implementation", RFC 1305, March 1992.

   [4]   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.

   [5]   Aboba, B. and J. Wood, "Authentication, Authorization and
         Accounting (AAA) Transport Profile", RFC 3539, June 2003.

   [6]   Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites for
         Transport Layer Security (TLS)", RFC 4279, December 2005.

   [7]   Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.1", RFC 4346, April 2006.

   [8]   Manner, J. and M. Kojo, "Mobility Related Terminology",
         RFC 3753, June 2004.

   [9]   Clancy, C., "Security Review of the Light Weight Access Point
         Protocol", May 2005,
         <http://www.cs.umd.edu/~clancy/docs/lwapp-review.pdf>.

   [10]  Rescorla et al, E., "Datagram Transport Layer Security",
         June 2004.

14.2.  Informational References

   [11]  "draft-ietf-capwap-protocol-binding-specification-ieee802dot11-
         00".

   [12]  Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by an On-
         line Database", RFC 3232, January 2002.

   [13]  Modadugu et al, N., "The Design and Implementation of Datagram
         TLS", Feb 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
   Research In Motion
   5090 Commerce Blvd
   Mississauga, ON  L4W 5M4
   Canada

   Phone: +1 905-629-4746 x4999
   Email: mmontemurro@rim.com


   Dorothy Stanley
   Aruba Networks
   1322 Crossman Ave
   Sunnyvale, CA  94089

   Phone: +1 630-363-1389
   Email: dstanley@arubanetworks.com























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Full Copyright Statement

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