CAPWAP Working Group P. Narasimhan
Internet-Draft Aruba Networks
Expires: December 2, 2005 D. Harkins
Trapeze Networks
S. Ponnuswamy
Aruba Networks
May 31, 2005
SLAPP : Secure Light Access Point Protocol
draft-narasimhan-ietf-slapp-01
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Copyright (C) The Internet Society (2005).
Abstract
The CAPWAP problem statement [3] describes a problem that needs to be
addressed before a wireless LAN (WLAN) network designer can construct
a solution composed of Wireless Termination Points (WTP) and Access
Controllers (AC) from multiple, different vendors. One of the
primary goals is to find a solution that solves the interoperability
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between the two classes of devices (WTPs and ACs) which then enables
an AC from one vendor to control and manage a WTP from another.
The interoperability problem is more general than as stated in the
CAPWAP problem statement [3] because it can arise out of other
networks that do not necessarily involve WLAN or any wireless
devices. A similar problem exists in any network that is composed of
network elements that are managed by a centralized controller where
these two classes of devices are from different vendors and need to
interoperate with each other such that the network elements can be
controlled and managed by the controller.
A possible solution to this problem is to split it into two parts -
one that is technology or application independent which serves as a
common framework across multiple underlying technologies, and another
that is dependent on the underlying technology that is being used in
the network. For example, methods and parameters used by an 802.11
AC to configure and manage a network of 802.11 WTPs are expected to
be quite different than that used by an equivalent 802.16 controller
to manage a network of 802.16 base stations. The architectural
choices for these two underlying technologies may also be
significantly different.
In this draft, we present a protocol that forms the common
technology-independent framework and the ability to negotiate and
add, on top of this framework, a control protocol that contains a
technology-dependent component to arrive at a complete solution. We
have also presented two such control protocols - an 802.11 Control
protocol, and another a more generic image download protocol, in this
draft.
Even though the text in this draft is written to specifically address
the problem stated in [3], the solution can be applied to any problem
that has a controller (equivalent to the AC) managing one or more
network elements (equivalent to the WTP).
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Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Conventions used in this document . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Protocol Description . . . . . . . . . . . . . . . . . . . 11
4.1.1 State Machine Explanation . . . . . . . . . . . . . . 11
4.2 Format of a SLAPP Header . . . . . . . . . . . . . . . . . 13
4.3 Version . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.4 Retransmission . . . . . . . . . . . . . . . . . . . . . . 14
4.5 Discovery . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5.1 SLAPP Discover Request . . . . . . . . . . . . . . . . 15
4.5.2 SLAPP Discover Response . . . . . . . . . . . . . . . 18
4.6 SLAPP Discovery Process . . . . . . . . . . . . . . . . . 19
4.6.1 WTP . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.6.2 AC . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5. Security Association . . . . . . . . . . . . . . . . . . . . . 23
5.1 Example Authentication Models (Informative) . . . . . . . 23
5.1.1 Mutual Authentication . . . . . . . . . . . . . . . . 24
5.1.2 WTP-only Authentication . . . . . . . . . . . . . . . 24
5.1.3 Anonymous Authentication . . . . . . . . . . . . . . . 24
6. SLAPP Control Protocols . . . . . . . . . . . . . . . . . . . 25
6.1 802.11 Control Protocol for SLAPP . . . . . . . . . . . . 25
6.1.1 Suppported CAPWAP Architectures . . . . . . . . . . . 25
6.1.2 Transport . . . . . . . . . . . . . . . . . . . . . . 28
6.1.3 Provisioning and Configuration of WTP . . . . . . . . 29
6.1.4 Protocol Operation . . . . . . . . . . . . . . . . . . 64
6.2 Image Download Protocol . . . . . . . . . . . . . . . . . 69
6.2.1 Image Download Packet . . . . . . . . . . . . . . . . 70
6.2.2 Image Download Request . . . . . . . . . . . . . . . . 70
6.2.3 Image Download Process . . . . . . . . . . . . . . . . 71
6.2.4 Image Download State Machine . . . . . . . . . . . . . 72
7. Security Considerations . . . . . . . . . . . . . . . . . . . 77
8. Extensibility to other technologies . . . . . . . . . . . . . 78
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 79
Intellectual Property and Copyright Statements . . . . . . . . 80
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1. Definitions
1.1 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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2. Introduction
The need for a protocol by which wireless LAN (WLAN) Access
Controllers (AC) can control and manage Wireless Termination Points
(WTP) from a different vendor has been presented in the CAPWAP
problem statement [3]. We believe that this problem is more general
than as stated in [3] and can be found in any application, including
non-wireless ones, that requires a central controller to control and
manage one or more network elements from a different vendor.
One way to solve the CAPWAP problem is to define a complete control
protocol that enables an AC from one vendor to control and manage a
WTP from a different vendor. But a solution that is primarily
focused towards solving the problem for one particular underlying
technology (IEEE 802.11, in this case) may find it difficult to
address other underlying technologies. Different underlying
technologies may differ on the set of configurable options, and
different architectural choices that are specific to that underlying
technology (similar to the local MAC vs. split MAC architectures in
802.11). The architectural choices that are good for one underlying
technology may not necessarily work for another. Not to forget that
there may be multiple architectural choices [2] even for the same
underlying technology. A monolithic control protocol that strives to
solve this problem for multiple technologies runs the risk of adding
too much complexity and not realizing the desired goals, or it runs
the risk of being too rigid and hampering technological innovation.
A different way to solve this problem is to split the solution space
into two components - one that is technology agnostic or independent,
and another that is specific to the underlying technology or even
different approaches for the same underlying technology. The
technology-independent component would be a common framework that
would be an important component of the solution to this class of
problems without any dependency on the underlying technology (i.e.
802.11, 802.16, etc.) being used. The technology-specific component
would be a control protocol that would be negotiated using this
common framework and can be easily defined to be relevant to that
technology without the need for having any dependency on other
underlying technologies. This approach also lends itself easily to
extend the solution as new technologies arise or as new innovative
methods to solve the same problem for an existing technology present
themselves later in the future.
In this draft, we present secure light access point protocol (SLAPP),
a technology-independent protocol by which network elements that are
meant to be centrally managed by a controller can discover one or
more controllers, perform a security association with one of them,
and negotiate a control protocol that they would use to perform the
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technology-specific components of the control and provisioning
protocol. We have also presented two control protocols in this draft
- an 802.11 control protocol for provisioning and managing a set of
802.11 WTPs, and an image download protocol that is very generic and
can be applied to any underlying technology.
Figure 1 shows the model by which a technology-specific control
protocol can be negotiated using SLAPP to complete a solution for a
certain underlying technology. The figure shows a control protocol
each for 802.11 and 802.16 technology components, but the SLAPP model
does not preclude multiple control protocols within a certain
technology segment. For example, a certain technology-specific
control protocol may choose to support only the local MAC
architecture [2] while deciding not to support the split MAC
architecture [2]. While the image download protocol is presented in
this draft, a SLAPP implementation MUST NOT assume that this control
protocol is supported by other SLAPP implementations.
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Negotiated
SLAPP Control
Protocol
+-------------------------+ +------------+
| | | |
| SLAPP | | Image |
| (technology-independent +-------+----->| Download |
| framework) | | | protocol |
| | | | |
| negotiate one control | | +------------+
| protocol here | |
+-------------------------+ |
| +------------+
| | |
| | 802.11 |
+----->| control |
| | protocol |
| | |
| +------------+
|
|
| +------------+
| | |
| | 802.16 |
+----->| control |
| | protocol |
| | |
| +------------+
|
| .......
Figure 1: SLAPP Protocol Model
The control protocols that are negotiable using SLAPP are expected to
be published ones that have gone through a review process in
standards bodies such as the IETF. The control protocols can either
re-use the security association created during SLAPP or have the
option of clearing all SLAPP state and restarting with whatever
mechanisms are defined in the control protocol.
Recently, there was a significant amount of interest in a similar
problem in the RFID space that has led to the definition of a simple
lightweight RFID reader protocol (SLRRP) [10]. It is quite possible
that SLRRP could be a technology-specific (RFID, in this case)
control protocol negoriated during a common technology-independent
framework.
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All of the text in the draft would seem to be written with a WLAN
problem in mind. Please note that while the letter of the draft does
position the solution to solve a CAPWAP-specific problem, the spirit
of the draft is to address the more general problem.
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3. Topology
The SLAPP protocol supports multiple topologies for interconnecting
WTPs and ACs as indicated in Figure 2.
In Figure 2, we have captured four different interconnection
topologies.
1. The WTP is directly connected to the AC without any intermediate
nodes. Many WTPs are deployed in the plenum of buildings and are
required to be powered over the Ethernet cable that is connecting
it to the network. Many ACs in the marketplace can supply power
over etherent and in the case where the AC is the one powering
the WTP, the WTP is directly connected to the AC.
2. The WTP is not directly connected to the AC, but both the AC and
the WTP are in the same L2 (broadcast) domain.
3. The WTP is not directly connected to the AC, and they are not
present in the same L2 (broadcast) domain. They are on two
different broadcast domains and have a node on the path that
routes between two or more subnets.
4. The fourth case is a subset of the third one with the exception
that the intermediate nodes on the path from the WTP to the AC
may not necessarily be in the same administrative domain. The
intermediate network may also span one or more WAN links that may
have lower capacity than if both the AC and the WTP are within
the same building or campus.
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+-----------------+ +-------+
| | (1) | |
| AC +------------+ WTP |
| | | |
+--------+--------+ +-------+
|
|
|
+---+---+
(2) | |
+------+ L2 +--------+
| | | |
| +---+---+ |
| |
| |
+-----+-----+ +---+---+ +-------+
| | | | (3)| |
| WTP | | L3 +----+ WTP |
| | | | | |
+-----------+ +---+---+ +-------+
|
|
|
+---+----+ +-------+
| | (4)| |
|Internet+----+ WTP |
| | | |
+--------+ +-------+
Figure 2: SLAPP Topology
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4. Protocol
4.1 Protocol Description
The SLAPP state machine for both the WTP and AC is shown in Figure 3.
Both the WTP and the AC discover each other, negotiate a control
protocol, perform a secure handshake to establish a secure channel
between them, and then use that secure channel to protect a
negotiated control protocol.
The WTP maintains the following variable for its state machine:
abandon: a timer which sets the maximum amount of time the WTP will
wait for an acquired AC to begin the DTLS handshake.
/--------\ /-----------\
| | | |
| v v |
| +-------------+ |
| C| discovering |<-\ |
| +-------------+ | |
| | | |
| v | |
| +-----------+ | |
\--| acquiring | | |
+-----------+ | |
| | |
v | |
+----------+ | |
C| securing |-----/ |
+----------+ |
| |
v |
+----------------+ |
| negotiated | |
C| control |-----/
| protocol |
+----------------+
Figure 3: SLAPP State Machine
4.1.1 State Machine Explanation
Note: the symbol "C" indicates an event which results in the state
remaining the same.
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Discovering
AC: this is a quiescent state for the AC in which it waits for
WTPs to request its acquisition. When a request is received
the AC transitions to Acquiring.
WTP: the WTP is actively discovering an AC. When the WTP receives
a response to its discovery request it transitions to
Acquiring.
Acquiring
AC: a discover request from a WTP has been received. If the
request is invalid or the AC wishes to not acquire the WTP it
drops the packet and transitions back to Discovering.
Otherwise a discovery response is sent and the AC transitions
to Securing.
WTP: a discover response from an AC has been received. If the
response is not valid the WTP transitions to Discovering,
otherwise it sets the abandon timer to a suitable value to
await a DTLS exchange. If the timer fires in Acquiring the WTP
transitions back to Discovering. If a DTLS "client hello" is
received the WTP transitions to Securing and cancels the
abandon timer.
Securing
AC: The AC performs the "client end" of the DTLS exchange. Any
error in the DTLS exchange results in the AC transitioning to
Discovering. When the DTLS exchange finishes the AC
transitions to Negotiated Control Protocol.
WTP: The WTP performs the "server end" of the DTLS exchange. Any
error in the DTLS exchange results in the WTP transitioning to
Discovering. When the DTLS exchange finishes the WTP
transitions to the Negotiated Control Protocol.
Negotiated Control Protocol
AC: the AC performs its side of the protocol agreed to during the
discovery process. Please refer to Section 6.1 for the SLAPP
802.11 control protocol. For the Image Download Protocol
example see section Section 6.2.
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WTP: the WTP performs its side of the protocol agreed to during
the discovery process. Please refer to Section 6.1 for the
SLAPP 802.11 control protocol. For the Image Download Protocol
example see section Section 6.2.
4.2 Format of a SLAPP Header
All SLAPP packets begin with the same header as shown in Figure 4.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SLAPP Header
Where:
Maj (4 bits): the major number of the SLAPP version
Min (4 bits): the minor number of the SLAPP version
Type (1 octet): the type of SLAPP message
Length (two octets): the length of the SLAPP message, including
the entire SLAPP header
The following types of SLAPP messages have been defined:
name type
------ ------
discovery request 1
discovery response 2
image download control 3
control protocol packet 4
reserved 5-255
4.3 Version
SLAPP messages include a version in the form of major.minor. This
document describes the 1.0 version of SLAPP, that is the major
version is one (1) and the minor version is zero (0).
Major versions are incremented when the format of a SLAPP message
changes or the meaning of a SLAPP message changes such that it would
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not be properly parsed by an older, existing version of SLAPP. Minor
versions are incremented when some incremental additions have been
made to SLAPP that enhance its capabilities or convey additional
information in a way that does not change the format or meaning of
the SLAPP message.
Future versions of SLAPP MAY NOT mandate support for earlier major
versions of SLAPP so an implementation MUST NOT assume that a peer
that supports version "n" will therefore support version "n - i"
(where both "n" and "i" are non-zero integers and "n" is greater than
"i").
A SLAPP implementation that receives a SLAPP message with a higher
major version number MUST drop that message. A SLAPP implementation
that receives a SLAPP message with a lower major version SHOULD drop
down to the version of SLAPP the peer supports. If that version of
SLAPP is not supported the message MUST be dropped. There may be
valid reasons for which a peer wishes to drop a SLAPP message with a
supported major version though.
A SLAPP implementation that receives a SLAPP message with a higher
minor version number MUST NOT drop that message. It MUST respond
with the minor version number that it supports and will necessarily
not support whatever incremental capabilities were added that
justified the bump in the minor version. A SLAPP implementation that
receives a SLAPP message with a lower minor version MUST NOT drop
that message. It SHOULD revert back to the minor version which the
peer supports and not include any incremental capabilities that were
added which justified the bump in the minor version.
4.4 Retransmission
SLAPP is a request response protocol. Discovery and security
handshake requests are made by the WTP and responses to them are made
by the AC. Image download packets are initiated by the AC and
acknowledged by the WTP (in a negative fashion, see Section 6.2).
Retransmissions are handled solely by the initiator of the packet.
After each packet for which a response is required is transmitted,
the sender MUST set a retransmission timer and resend the packet upon
its expiry. The receiver MUST be capable of either regenerating a
previous response upon receipt of a retransmitted packet or caching a
previous response and resending upon receipt of a retransmitted
packet.
The retransmission timer MUST be configurable and default to one (1)
second. No maximum or minimum for the timer is specified by this
version of SLAPP.
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Each time a retransmission is made a counter SHOULD be incremented
and the number of retransmissions attempted by a sender before giving
up and declaring a SLAPP failure SHOULD be four (4)-- that is, the
number of attempts made for each packet before declaring failure is
five (5).
The exception to this rule is Image Download packets which are not
individually acknowledged by the WTP (see Section 6.2). The final
packet is acknowledged and lost packets are indicated through Image
Download Requests.
4.5 Discovery
When a WTP boots up and wants to interoperate with an Access
Controller so that it can be configured by the AC, one of the first
things it needs to do is to discover one or more ACs in its network
neighborhood. This section contains the details of this discovery
mechanism.
As described in Section 3, an AC and a WTP could reside in the same
layer 2 domain, or be separated by a layer 3 cloud including
intermediate clouds that are not under the same administrative domain
(for example, an AC and a WTP separated by a wide-area public
network). So any proposed discovery mechanism should have provisions
to enable a WTP to discover an AC across all these topologies.
We assume that a WTP prior to starting the discovery process has
already obtained an IP address on its wired segment.
4.5.1 SLAPP Discover Request
The SLAPP discovery process is initiated by sending a SLAPP discover
request packet. The packet can be addressed to the broadcast IP
address, a well known multicast address, or (if the IP address of an
AC is either configured prior to the WTP booting up or is learned
during the boot-up sequence) addressed to a unicast IP address. Lack
of a response to one method of discovery SHOULD result in the WTP
trying another method of discovery. The SLAPP discover request
packet is a UDP packet addressed to port [TBD] designated as the
SLAPP discovery port. The source port can be any random port. The
payload of the SLAPP discover request packet is shown in Figure 5.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | Type = 1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transaction ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Identifier (continued) | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP HW Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP SW Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n controltypes| control type | . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SLAPP Discover Request
4.5.1.1 Transaction ID
The transaction ID is a randomly generated 32-bit number that is
maintained during one phase of the SLAPP discovery process. It is
generated by a WTP starting a discovery process. When one discovery
method fails to find an AC and the WTP attempts another discovery
method it MUST NOT reuse the Transaction ID. All ACs that intend to
respond to a SLAPP discover request must use the same value for this
field as in the request frame.
4.5.1.2 WTP Identifier
This field allows the WTP to specify a unique identifier for itself.
This MAY be, for instance, its 48-bit MAC address or it could be any
other string such as a serial number.
4.5.1.3 Flags
The flags field is used to indicate certain things about the discover
request. For example, bit 0 in the flags field indicates whether the
discover request packet is being sent to the AC, if unicast, based on
a configuration at the WTP or based on some other means of discovery.
This bit should always be set to the discover mode if the SLAPP
discover request packet is being sent to either a broadcast or
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multicast address. Here are the valid values for various bits in the
Flags field.
Bit 0:
0 - Configuration mode
1 - Discover mode
Bits 1-15:
Must always be set to 0 by the transmitter
Must be ignored by the receiver
4.5.1.4 WTP Vendor ID
This 32-bit field is the WTP vendor's SMI enterprise code in network
octet order (these enterprise codes can be obtained from, and
registered with, IANA).
4.5.1.5 WTP HW Version
This 32-bit field indicates the version of hardware present in the
WTP. This is a number that is totally left to the WTP vendor to
choose.
4.5.1.6 WTP SW Version
This 32-bit field indicates the version of software present in the
WTP. This is a number that is totally left to the WTP vendor to
choose.
4.5.1.7 number of control types
This 8-bit field indicates the number of 8-bit control protocol
indicators that follow it and therefore implicitly indicates the
number of different control protocols the the WTP is capable of
supporting. This number MUST be at least one (1).
4.5.1.8 control types
This 8-bit field indicates the type of control protocol the WTP
supports and is willing to use when communicating with an AC. There
MAY be multiple "control type" indicators in a single SLAPP Discover
Request.
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Valid control types
-------------------
0 - RESERVED (MUST not be used)
1 - Image Download Control Protocol
2 - 802.11 SLAPP control protocol
3-255 - RESERVED (to IANA)
4.5.2 SLAPP Discover Response
An AC that receives a SLAPP discover request packet from a WTP can
choose to respond with a SLAPP discover response packet. The format
of the SLAPP discover response packet is shown in Figure 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | Type = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transaction ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| WTP Identifier (continued) | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC HW Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC HW Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AC SW Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| control type |
+-+-+-+-+-+-+-+-+
Figure 6: SLAPP Discover Response
The SLAPP discover response packet is a UDP packet. It is always
unicast to the WTP's IP address. The source IP address is that of
the AC sending the response. The source port is the SLAPP discover
port [TBD] and the destination port is the same as the source port
used in the SLAPP discover request. The WTP's MAC address and the
transaction ID must be identical to the values contained in the SLAPP
discover request. The Status field indicates to the WTP whether the
AC is either accepting the discover request and is willing to allow
the WTP to proceed to the next stage (ACK) or whether it is denying
the WTP's earlier request (NACK). The AC includes its own vendor ID,
hardware and software versions in the response.
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4.5.2.1 Transaction ID
The value of the Transaction ID field should be identical to its
value in the SLAPP discover request packet sent by the WTP.
4.5.2.2 WTP Identifier
The WTP Identifier that was sent in the corresponding SLAPP discover
request frame.
4.5.2.3 Flags
This field is unused by this version of SLAPP. It MUST be set to
zero (0) on transmission and ignored upon receipt.
4.5.2.4 AC Vendor ID
If the value of the status field is a 1, indicating that the AC is
sending a successful response, then the values in this field and the
following two are valid. The 32-bit AC Vendor ID points to the
vendor ID of the AC. If the value of the status field is not 1, then
this field should be set to 0 by the AC and ignored by the WTP.
4.5.2.5 AC HW Version
If the value of the status field is 1, then this 32-bit field
contains the value of the AC's hardware version. This value is
chosen by the AC vendor. If the value of the status field is not a
1, then this field should be set to 0 by the AC and ignored by the
WTP.
4.5.2.6 AC SW Version
If the value of the status field is 1, then this 32-bit field
contains the value of the AC's software version. This value is
chosen by the AC vendor. If the value of the status field is not a
1, then this field should be set to 0 by the AC and ignored by the
WTP.
4.5.2.7 Control Type
The control type the AC will use to communicate with the WTP. This
value MUST match one of the control types passed in the corresponding
SLAPP Discover Request.
4.6 SLAPP Discovery Process
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4.6.1 WTP
There are multiple ways in which a WTP can discover an AC.
1. Static configuration: An administrator, prior to deploying a WTP,
can configure an IP address of an AC on the WTP's non-volatile
memory. If this is the case, then the SLAPP discover request
packet is addressed to the configured IP address.
2. DHCP options: As part of the DHCP response, the DHCP server could
be configured to use option 43 to deliver the IP address of an AC
to which the WTP should address the SLAPP discover request
packet. If the IP address of an AC is handed to the WTP as part
of the DHCP response, then the WTP should address the SLAPP
discover request packet to this IP address.
3. DNS configuration: Instead of configuring a static IP address on
the WTP's non-volatile memory, an administrator can configure a
FQDN of an AC. If the FQDN of an AC is configured, then the WTP
queries its configured DNS server for the IP address associated
with the configured FQDN of the AC. If the DNS query is
successful and the WTP acquires the IP address of an AC from the
DNS server, then the above discover request packet is addressed
to the unicast address of the AC.
4. Broadcast: The WTP sends a discover request packet addressed to
the broadcast IP address with the WTP's IP address as the source.
A network administrator, if necessary, could configure the
default router for the subnet that the WTP is on with a helper
address and unicast it to any address on a different subnet.
5. IP Multicast: A WTP can send the above payload to a SLAPP IP
multicast address [TBD].
6. DNS: If there is no DNS FQDN configured on the WTP, and the WTP
is unable to discover an AC by any of the above methods, then it
should attempt to query the DNS server for a well known FQDN of
an AC [TBD]. If this DNS query succeeds, then the WTP should
address the SLAPP discover request packet to the unicast address
of the AC.
The above process is summarized in the sequence shown in Figure 7.
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SLAPP discovery start:
Static IP address config option:
Is a static IP address for an AC configured?
If yes, send SLAPP discover request to that unicast IP address
SLAPP discover response within discovery_timer?
If yes, go to "done"
If not, go to "Static FQDN config option"
If not, go to "Static FQDN config option"
Static FQDN config option:
Is a static FQDN configured?
If yes, send a DNS query for the IP address for the FQDN.
Is DNS query successful?
If yes, send SLAPP discover request to that IP address
SLAPP discover response within discovery timer?
If yes, go to "done"
If not, go to "DHCP options option"
If not, go to "DHCP options option"
DHCP options option:
Is the IP address of an AC present in the DHCP response?
If yes, send SLAPP discover request to the AC's IP addr
SLAPP discover response within discovery timer?
If yes, go to "done"
If not, go to "Broadcast option"
If not, go to "Broadcast option"
Broadcast option:
Send SLAPP discover packet to the broadcast address
SLAPP discover response within discovery timer?
If yes, go to "done"
If not, go to "Multicast option"
Multicast option:
Send SLAPP discover packet to the SLAPP multicast address
SLAPP discover response within discovery timer?
If yes, go to "done"
If not, go to "DNS discovery option"
DNS discovery option:
Query the DNS server for a well known DNS name
Is the DNS discovery successful?
If yes, send SLAPP discover request to that IP addr
SLAPP discover response within discovery timer?
If yes, go to "done"
If not, go to "SLAPP discovery restart"
If not, go to "SLAPP discovery restart"
SLAPP discovery restart:
Set timer for SLAPP discovery idle timer
When timer expires, go to "SLAPP discovery start"
done:
go to the next step
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Figure 7
4.6.2 AC
When an AC receives a SLAPP discover request it must determine
whether it wishes to acquire the WTP or not. An AC MAY only agree to
acquire those WTPs whose WTP Identifiers are statically configured in
its configuration. Or an AC that is willing to gratuitously acquire
WTPs MAY accept any request pending authentication. An AC MUST only
choose to acquire WTPs that speak a common Negotiated Control
protocol but other factors may influence its decision. For instance,
if the Negotiated Control Protocol is the Image Download protocol
defined in this memo the AC MUST NOT acquire a WTP for which it does
not have a compatible image to download as determined by the WTP's HW
Vendor ID, HW Version and Software Version. Whatever its decision,
the AC MUST respond one of two ways.
1. The AC sends a SLAPP discover response indicating its agreement
to acquire the WTP.
2. The AC silently drops the SLAPP discover request and does not
respond at all.
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5. Security Association
Once an AC has been discovered by a WTP and agreed to acquire it (by
sending a Discovery Response) it will initiate a DTLS [7] [9]
exchange with the WTP by assuming the role of the "client". The WTP
assumes the role of the "server". The port used by both the WTP and
AC for this exchange will be [TBD].
An obvious question is "why is the AC acting as a client?" The
reason is to allow for non-mutual authentication in which the WTP is
authenticated by the AC (see Section 5.1.2).
Informational note: DTLS is used because it provides a secure and
connectionless channel using a widely accepted and analyzed protocol.
In addition, the myriad of authentication options in DTLS allows for
a wide array of options with which to secure the channel between the
WTP and the AC-- mutual and certificate based; asymmetric or non-
mutual authentication; anonymous authentication; etc. Furthermore,
DTLS defines its own fragmentation and reassembly techniques as well
as ways in which peers agree on an effective MTU. Using DTLS
obviates the need to redefine these aspects of a protocol and
therefore lessens code bloat as the same problem doesn't need to be
solved yet again in another place.
Failure of the DTLS handshake protocol will cause both parties to
abandon the exchange. The AC SHOULD blacklist this WTP for a period
of time to prevent a misconfigured WTP from repeatedly discovering
and failing authentication. The WTP MUST return to the discovery
state of SLAPP to locate another suitable AC with which it will
initiate a DTLS exchange.
Once the DTLS handshake has succeeded the WTP and AP transition into
"image download state" and protect all further SLAPP messages with
the DTLS-negotiated cipher suite.
5.1 Example Authentication Models (Informative)
Any valid cipher suite in [8] can be used to authenticate the WTP
and/or the AC. Different scenarios require different authentication
models. The following examples are illustrative only and not meant
to be exhaustive.
Since neither side typically involves a human being a username/
password based authentication is not possible.
Zero-config requirements on certain WTP deployments can predicate
certain authentication options and eliminate others.
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5.1.1 Mutual Authentication
When mutually authenticating, the WTP authenticates the AC, thereby
ensuring that the AC to which it is connecting is a trusted AC, and
the AC authenticates the WTP, thereby ensuring that the WTP that is
connecting is a trusted WTP.
Mutual authentication is typically achieved by using certificates on
the WTP and AC which ensure public keys each party owns. These
certificates are digitally signed by a Certification Authority, a
trusted third party.
Enrolling each WTP in a Certification Authority is outside the scope
of this document but it should be noted that a manufacturing
Certification Authority does not necessarily provide the level of
assurance necessary as it will only guarantee that a WTP or AC was
manufactured by a particular company and cannot distinguish between a
trusted WTP and a WTP which is not trusted but was purchased from the
same manufacturer as the AC.
5.1.2 WTP-only Authentication
Some deployments may only require the WTP to authenticate to the AC
and not the other way around.
In this case the WTP has a keypair which can uniquely identify it
(for example, using a certificate) and that keypair is used in a
"server-side authentication" [8] exchange.
This authentication model does not authenticate the AC and a rogue AC
could assert control of a valid WTP. It should be noted, though,
that this will only allow the WTP to provide service for networks
made available by the rogue AC. No unauthorized network access is
possible.
5.1.3 Anonymous Authentication
In some deployments it MAY just be necessary to foil the casual
snooping of packets. In this case an unauthenticated, but encrypted,
connection can suffice. Typically a Diffie-Hellman exchange is
performed between the AC and WTP and the resulting unauthenticated
key is used to encrypt traffic between the AC and WTP.
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6. SLAPP Control Protocols
In this section, we describe two extensions for SLAPP - one that is
specific to 802.11 WLANs and another that is a technology neutral
protocol by which an AC can download a bootable image to a WTP.
6.1 802.11 Control Protocol for SLAPP
This section describes a SLAPP extension that is targeted towards
WTPs and ACs implementing the IEEE 802.11 WLAN standard. This
extension contains all the technology-specific component that will be
used by an AC to control and manage 802.11 WTPs.
6.1.1 Suppported CAPWAP Architectures
The CAPWAP architecture taxonomy document [2] describes multiple
architectures that are in use today in the WLAN industry. While
there is a wide spectrum of variability present in these documented
architectures, supporting every single variation or choice would lead
to a complex protocol and negotiation phase. In the interest of
limiting the complexity of the 802.11 component, we have limited the
negotiation to four different architectural choices as listed below.
Local MAC, bridged mode : This mode of operation falls under the
Local MAC architecture. The 802.11 MAC is terminated at the WTP.
The WTP implements an L2 bridge that forwards packets between its
WLAN interface and its ethernet interface.
Local MAC, tunneled mode : This mode of operation also falls under
the Local MAC architecture where the 802.11 MAC is terminated at
the WTP. The difference between this mode and the previous one is
that in this mode, the WTP tunnels 802.3 frames to the AC using
the mechanisms defined in Section 6.1.2.
Split MAC, L2 crypto at WTP : This mode of operation falls under the
split MAC architecture. The 802.11 MAC is split between the WTP
and the AC, the exact nature of the split is described in
Section 6.1.1.2. The L2 crypto functions are implemented in the
WTP are the ones used to satisfy this function irrespective of
whether the AC is also capable of this function or not. The WTP
tunnels L2 frames to the AC using mechanisms defined in
Section 6.1.2.
Split MAC, L2 crypto at AC : This mode of operation also falls under
the split MAC architecture. The difference between this one and
the previous one is that the L2 crypto functions implemented in
the AC are used to satisfy this function irrespective of whether
these functions are also available at the WTP or not. The WTP
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tunnels L2 frames to the AC using mechanisms defined in
Section 6.1.2.
6.1.1.1 Local MAC
The Local MAC architecture as documented in the CAPWAP architecture
taxonomy document [2] performs all 802.11 frame processing at the
WTP. The conversion from 802.11 to 802.3 and vice-versa is also
implemented at the WTP. This would mean that other functions like
fragmentation/reassembly of 802.11 frames, encryption/decryption of
802.11 frames is implemented at the WTP.
6.1.1.1.1 Bridged Mode
In this sub-mode of the Local MAC architecture, the 802.11 frames are
converted to 802.3 frames and bridged onto the Ethernet interface of
the WTP. These frames may be tagged with 802.1Q VLAN tags assigned
by the AC.
6.1.1.1.2 Tunneled Mode
In this sub-mode of the Local MAC architecture, the 802.11 frames are
converted to 802.3 frames and are tunneled (using the tunneling
mechanism defined in Section 6.1.2) to the AC that the WTP is
attached to. These frames may be tagged with 802.1Q VLAN tags
assigned by the AC.
6.1.1.2 Split MAC
In the split MAC architecture, the MAC functions of an 802.11 AP are
split between the WTP and the AC. The exact nature of the split is
dependent upon the sub-modes listed in this section. In both cases,
frames are tunneled to the AC using the mechanism defined in
Section 6.1.2.
Some of these split MAC architectures convert the 802.11 frames into
802.3 frames, which may be 802.1Q tagged using tags assigned by the
AC, while other of these split MAC architectures will tunnel the
entire 802.11 frame to the AC. The AC and WTP agree on what type of
frame will be tunneled during the control protocol registration
Section 6.1.3
6.1.1.2.1 L2 Crypto at the WTP
For this sub-mode of the split MAC architecture, the 802.11 AP
functions are split as follows:
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At the WTP
802.11 control frame processing
802.11 encryption and decryption
802.11 fragmentation and reassembly
Rate Adaptation
802.11 beacon generation
Power-save buffering and TIM processing
At the AC
802.11 Management frame processing
802.11 DS and portal
Split MAC implementations of this kind may tunnel either 802.11 or
802.3 frames between the AC and the WTP.
6.1.1.2.2 L2 Crypto at the AC
For this sub-mode of the split MAC architecture, the 802.11 AP
functions are split as follows:
At the WTP
802.11 control frame processing
Rate Adaptation
802.11 beacon generation
Power-save buffering and TIM processing
At the AC
802.11 Management frame processing
802.11 encryption and decryption
802.11 fragmentation and reassembly
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802.11 DS and portal
Split MAC implementations of this kind tunnel 802.11 frames between
the AC and the WTP.
6.1.2 Transport
The 802.11 Control protocol has two components, one for transporting
the specific control and provisioning messages and another to tunnel
data traffic from the WTP to the AC.
The SLAPP 802.11 Control Protocol uses the Generic Routing
Encapsulation (GRE) [4] to encapsulate L2 frames. Depending on
whether and how an architecture splits its MAC some architectures may
tunnel 802.11 frames directly to the AC while others may tunnel 802.3
frames which may be optionally 802.1Q tagged using tags assigned by
the AC.
The delivery mechanism of these GRE packets is IP. Therefore the IP
protocol of the outer packet is 47, indicating a GRE header follows.
When GRE encapsulates 802.11 frames the ether type in the GRE header
is TBD; when GRE encapsulates 802.3 frames the ether type in the GRE
header is TBD2.
Since IP is the delivery mechanism all issues governing fragmentation
and reassembly are handled by [5].
6.1.2.1 SLAPP 802.11 Control Protocol Header
When using the 802.11 control protocol the type of SLAPP message is
four (4), "control protocol packet". In this case a two (2) octet
field is appended to the SLAPP header to indicate the control
protocol type as shown in Figure 8. The SLAPP 802.11 Control
Protocol takes place in the "negoatiated control protocol" phase of
Section 4.1 and all SLAPP 802.11 Control Protocol messages are
therefore secured by the security association created immediately
prior to entering that phase.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 802.11 Control Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: SLAPP Control Protocol Header
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Where valid 802.11 Control Protocol Types are:
1 : Registration request - sent from WTP to AC
2 : Registration response - sent from AC to WTP
3 : De-registration request - sent by either WTP or AC
4 : De-registration response - sent by the recipient of the
corresponding request
5 : Configuration request - sent by WTP to AC
6 : Configuration response - sent by AC to WTP
7 : Configuration update - sent by AC to WTP
8 : Configuration acknowledgment - sent by the WTP to AC
9 : Status request - sent by the AC to the WTP
10 : Status response - sent by the WTP to the AC
11 : Statistics request - sent by the AC to the WTP
12 : Statistics response - sent by the WTP to the AC
13 : Event - sent by the WTP to the AC
14 : Keepalive - sent either way
15 : Key Config Request - sent by the AC to the WTP
16 : Key Config Response - sent by the WTP to the AC
6.1.3 Provisioning and Configuration of WTP
All basic configuration functions are applicable per-ESSID per-radio
in a WTP. Some WTPs MAY support more than one ESSID per-radio, while
all WTPs MUST support at least one ESSID per-radio, which may be
considered the primary ESSID in case of multiple ESSID support. All
per-WTP configurations and capabilities (e.g., number of radios) are
handled as part of the discovery and initialization process.
The provisioning of the regulatory domain of a WTP is beyond the
scope of this document. A WTP, once provisioned for a specific
regulatory domain MUST restrict the operational modes, channel,
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transmit power and any other necessary limits based on the knowledge
contained within its software image and hardware capabilities. The
WTP MUST communicate its capabilities limited by the regulatory
domain as well as by the WTP hardware, if any, to the AC during the
capability exchange.
The allocation and assignment of BSSIDs to the primary interface and
to the virtual AP interfaces, if supported, are outside the scope of
this document.
6.1.3.1 Information Elements
Information elements are used to communicate capability,
configuration, status, and statistics information between the AC and
the WTP.
6.1.3.1.1 Structure of an Information Element
The structure of an information element is show below. The element
ID starts with an element ID octet, followed by a 1-octet length and
the value of the element ID whose length is indicated in the Length
field. The maximum length of an element is 255 octets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Element ID | Length | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.1.3.1.2 CAPWAP Mode
This element defines the MAC architecture modes (Section 6.1.1).
Element ID : 1
Length : 1
Value : The following values are defined.
Bit 0 : CAPWAP mode 1 - Local MAC, bridged mode
Bit 1 : CAPWAP mode 2 - Local MAC, tunneled mode
Bit 2 : CAPWAP mode 3 - Split MAC, WTP encryption, 802.3 tunneling
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Bit 3 : CAPWAP mode 4 - Split MAC, WTP encryption, 802.11
tunneling
Bit 4 : CAPWAP mode 5 - Split MAC, AC encryption, 802.11 tunneling
Bits 5-7 : set to 0
When this element is included in the capabilities message, then the
setting of a bit indicates the support for this CAPWAP mode at the
WTP. When this element is used in configuration and status messages,
then exactly one of bits 0-4 MUST be set.
6.1.3.1.3 Number of WLAN Interfaces
This element refers to the number of 802.11 WLAN present in the WTP.
Element ID : 2
Length : 1
Value : 0-255
6.1.3.1.4 WLAN Interface Index
This element is used to refer to a particular instance of a WLAN
interface when used in configuration and status messages. When used
within a recursion element, the elements within the recursion element
correspond to the WLAN interface specified in this element.
Element ID : 3
Length : 1
Value : 0 - (Number of WLAN interfaces - 1)
6.1.3.1.5 WLAN Interface Hardware Vendor ID
This element is the WLAN Interface hardware vendor's SMI enterprise
code in network octet order (these enterprise codes can be obtained
from, and registered with, IANA). This field appears once for each
instance of WLAN interface present in the WTP.
Element ID : 4
Length : 4
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Value : 32-bit value
6.1.3.1.6 WLAN Interface Type ID
This element is an ID assigned by the WLAN Interface hardware vendor
to indicate the type of the WLAN interface. It is controlled by the
hardware vendor and the range of possible values is beyond the scope
of this document. This field appears once for each instance of WLAN
interface present in the WTP.
Element ID : 5
Length : 4
6.1.3.1.7 Regulatory Domain
If a regulatory domain is provisioned in the WTP, then the WTP
indicates this by including this element in the capabilities list.
If this information is not available at the WTP, then this element
SHOULD not be included in the capabilities list. The process by
which this information is provisioned into the WTP is beyond the
scope of this document.
Element ID : 6
Length : 4
Value : ISO code assigned to the regulatory domain
6.1.3.1.8 802.11 PHY mode and Channel Information
This element indicates the list of 802.11 PHY modes supported by the
WTP along with a list of channels and maximum power level supported
for this mode. This element appears once for each instance of WLAN
interface at the WTP. There could be multiple instances of this
element if the WLAN interface supports multiple PHY types.
Element ID : 7
Length : Variable
Valid : This field consists of
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PHY mode : With a length of 1 octet with value values as follows:
0 : Radio Disabled/Inactive
1 : IEEE 802.11b
2 : IEEE 802.11g
3 : IEEE 802.11a
4-255 : Reserved
Power Level : In the capabilities messages, this indicates the
maximum power level supported in this mode by the WTP, while in
the configuration and status messages this field indicates the
desired power level or the current power level that the WTP is
operating at. The field has a length of 1 octet and the power
level is indicated in dBm.
Channel Information : A variable number of 2-octet values that
indicate the center frequencies (in KHz) of all supported
channels in this PHY mode.
When this element is used in configuration and status messages, the
power level field indicates the desired or current operating power
level. The channel field has exactly one 2-octet value indicating
the desired or current operating frequency.
6.1.3.1.9 Cryptographic Capability
In the capabilities message, this element contains the list of
cryptographic algorithms that are supported by the WTP. This appears
once for each instance of the WLAN interface present in the WTP. In
configuration and status messages, this element is used to indicate
the configured cryptographic capabilities at the WTP.
Element ID : 8
Length : 1
Value : The following bits are defined.
Bit 0 : WEP
Bit 1 : TKIP
Bit 2 : AES-CCMP
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Bits 3-7 : Reserved
6.1.3.1.10 Other IEEE 802.11 Standards Support
This element contains a bitmap indicating support at the WTP for
various IEEE 802.11 standards.
Element ID : 9
Length : 4
Value : A bitmap as follows
Bit 0 : WPA
Bit 1 : 802.11i
Bit 2 : WMM
Bit 3 : WMM-SA
Bit 4 : U-APSD
Bits 5-32 : Reserved
6.1.3.1.11 Antenna Information Element
In the capabilities message, this element is formatted as follows
Element ID : 10
Length : 4
Value : Formatted as follows
Bits 0-7 : Number of Antennae
Bit 8 : Individually Configurable, 0 = No, 1 = Yes
Bit 9 : Diversity support, 0 = No, 1 = Yes
Bit 10 : 0 = Internal, 1 = External
Bits 11-31 : Reserved
In configuration and status messages, this element is formatted as
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follows:
Element ID : 10
Length : 4
Value : Formatted as follows
Bits 0-7 : Antenna Number - is a number between 0 and the
number of antennae indicated by the WTP. The value is valid
only if Bit 8 is set, otherwise it MUST be ignored
Bit 8 : Antenna Select - if this bit is reset then the antenna
selection is left to the algorithm on the WTP. If this bit is
set, then the Antenna Number field indicates the antenna that
should be used for transmit and receive.
Bits 9-31 : Reserved
6.1.3.1.12 Number of BSSIDs
This element indicates the number of BSSIDs supported by the WLAN
interface. This element is optional in the capabilities part of the
registration request message and if it is absent, then the number of
BSSIDs is set to 1. This element appears once for each instance of a
WLAN interface present in the WTP.
Element ID : 11
Length : 1
Value : The number of BSSIDs that the WLAN interface is capable of
supporting.
6.1.3.1.13 BSSID Index
This element is used when sending configuration or status specific to
a certain BSSID in the WTP.
Element ID : 12
Length : 1
Valid values are from 0 to (Number of BSSIDs -1)
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6.1.3.1.14 ESSID
This element is used in configuration and status messages to either
configure the ESSID on a certain BSSID or report the current
operating value.
Element ID : 13
Length : Variable, between 0 and 32 both inclusive
Value : Variable, contains ASCII characters.
There is no default value for this parameter.
6.1.3.1.15 ESSID Announcement Policy
This element is used in configuration and status messages to control
the announcement of the ESSID in 802.11 beacons. For the local MAC
modes of operation, this field is also used to control whether the
WTP should respond to probe requests that have a NULL ESSID in them.
Element ID : 14
Length : 1
Value : Defined as follows
Bit 0 : ESSID announcement, 0 = Hide ESSID, 1 = Display ESSID in
802.11 beacons. The default value for this bit is 1.
Bit 1 : Probe Response policy, 0 = Respond to probe requests that
contain a NULL ESSID, 1 = Respond only to probe requests that
match the configured ESSID. The default value for this bit is
0.
Bit 2-7 : Reserved
6.1.3.1.16 Beacon Interval
This element is used to configure the beacon interval on a BSSID on
the WTP.
Element ID : 15
Length : 2
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Value : Valid values for the beacon interval as allowed by IEEE
802.11
The default value for this parameter is 100.
6.1.3.1.17 DTIM period
This element is used to configure the DTIM period on a BSSID present
on the WTP.
Element ID : 16
Length : 2
Value : Valid values for the DTIM period as allowed by IEEE 802.11
The default value for this parameter is 1.
6.1.3.1.18 Basic Rates
Configure or report the configured set of basic rates.
Element ID : 17
Length : 4
Value : Each of the bits in the following list is interpreted as
follows. If the bit is set, then that particular rate is to be
configured as a basic rate. If the bit is reset, then the rate is
not to be configured as a basic rate.
Bit 0 : 1 Mbps
Bit 1 : 2 Mbps
Bit 2 : 5.5 Mbps
Bit 3 : 11 Mbps
Bit 4 : 6 Mbps
Bit 5 : 9 Mbps
Bit 6 : 12 Mbps
Bit 7 : 18 Mbps
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Bit 8 : 24 Mbps
Bit 9 : 36 Mbps
Bit 10 : 48 Mbps
Bit 11 : 54 Mbps
Bits 12-31 : Reserved
6.1.3.1.19 Supported Rates
Configure or report the configured set of basic rates.
Element ID : 18
Length : 4
Value : Each of the bits in the following list is interpreted as
follows. If the bit is set, then that particular rate is to be
configured as a supported rate. If the bit is reset, then the
rate is not to be configured as a supported rate.
Bit 0 : 1 Mbps
Bit 1 : 2 Mbps
Bit 2 : 5.5 Mbps
Bit 3 : 11 Mbps
Bit 4 : 6 Mbps
Bit 5 : 9 Mbps
Bit 6 : 12 Mbps
Bit 7 : 18 Mbps
Bit 8 : 24 Mbps
Bit 9 : 36 Mbps
Bit 10 : 48 Mbps
Bit 11 : 54 Mbps
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Bits 12-31 : Reserved
6.1.3.1.20 802.11 Retry Count
This element is used to configure long and short retries for each
BSSID present on the WTP.
Element ID : 19
Length : 2
Value : as follows
Bits 0-7 : Short retry count, default value is 3.
Bits 8-15 : Long retry count, default value is 3.
6.1.3.1.21 Fragmentation Threshold
This element is used to configure the fragmentation threshold on a
BSSID present on the WTP.
Element ID : 20
Length : 2
Value : Valid values for the fragmentation threshold as allowed by
IEEE 802.11.
The default value for this parameter is 2346.
6.1.3.1.22 RTS Threshold
This element is used to configure the RTS threshold on a BSSID
present on the WTP.
Element ID : 21
Length : 2
Value : Valid values for RTS threshold as allowed by IEEE 802.11.
The default value for this parameter is 2346.
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6.1.3.1.23 Short/Long Preamble
This element is used to configure the preamble type used for
transmission in 802.11b mode.
Element ID : 22
Length : 1
Value : defined as follows
0 : Disable Short preamble
1 : Enable Short preamble
2-255 : Reserved
The default value for this parameter is 0.
6.1.3.1.24 802.1Q Tag
This element is used to configure the tagging of packets belonging to
a particular SSID when transfered between the AC and the WTP in
CAPWAP modes 2-3, or before the WTP bridges the 802.3 frame to its
wired interface when operating in CAPWAP mode 1.
Element ID : 23
Length : 2
Value : 802.1Q tag
If this element is absent in the configuration, then the WTP MUST
assume that no tagging is required and should expect to receive
untagged frames on frames destined towards the wireless interface.
6.1.3.1.25 SLAPP Registration ID
A successful registration response from an AC to a WTP MUST contain
this element. It is used in messages between the WTP and the AC on
all other messages during the duration for which the registration is
active.
Element ID : 24
Length : 4
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Value : a 32-bit unsigned number allocated by the AC
6.1.3.1.26 WTP Name
The AC uses this element to assign a string of ASCII characters to
the WTP.
Element ID : 25
Length : Variable, between 0 and 64 both inclusive
Value : A variable length string of ASCII characters
6.1.3.1.27 Event Filter
The AC uses this element to assign importance to events, enable or
disable notification, and to configure the global event notification
policy. When the Event Identifier is 0, this element serves as a
global notification policy message. The bitmap indicates the types
of events that require the WTP to generate a notification. When the
Event Identifier is non-zero, this element is used to configure a
specific event for notification and its importance level. The
importance level is specified by setting exactly one bit in the
bitmap. If none of the bits are set in the bitmap, the element
should be interpreted as a cancellation request. The WTP should stop
sending notifications for the corresponding event specified in the
Element Identifier.
Element ID : 26
Length : 4
Value : defined as follows
Bits 0 - 15: Event Identifier
Bit 16: Fatal - The system is not usable
Bit 17: Alert - Immediate action is required
Bit 18: Critical
Bit 19: Error
Bit 20: Warning
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Bit 21: Notification
Bit 22: Informational
Bit 23: Debug
Bits 24 - 31: Reserved
6.1.3.1.28 Radio Mode
The AC uses this element to indicate the mode of operation for the
radio for each WLAN interface.
Element ID : 27
Length : 1
Value : The following are valid values.
0 : Radio is disabled
1 : Radio is enabled
2-255 : Reserved
6.1.3.1.29 IEEE 802.11e Element
The AC uses this element to configure 802.11e functions at the WTP
Element ID : 28
Length : 4
Value : A bitmap as follows
Bit 0 : WMM
Bit 1 : WMM-SA
Bit 2 : U-APSD
Bits 3-32 : Reserved
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6.1.3.1.30 Configuration Statistics
This element defines the statistics relating to configuration and
registration events as seen by the WTP.
Element ID : 29
Length : 32
Value : The value is as follows.
* Configuration Requests : 4 octets - Number of configuration
request messages sent by the WTP since the last reboot or reset
of the counters
* Configuration Responses : 4 octets
* Configuration Updates : 4 octets
* Configuration ACKs : 4 octets
* Registration Requests : 4 octets
* Registration Responses : 4 octets
* De-registration requests : 4 octets
* De-registration responses : 4 octets
6.1.3.1.31 Transmit Frame Counters
This information element contains a set of counters relating to the
transmit side of the wireless link at the WTP. These counters apply
to either a BSS or an Access Category (if WMM is enabled).
Element ID : 30
Length : 112 octets
Value : The value of this element is defined as follows.
* Total received from the network : 4 octets
* Successfully transmitted frames (total) : 4 octets
* Successfully transmitted 802.11 Mgmt frames : 4 octets
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* Successfully transmitted 802.11 Data frames : 4 octets
* Transmitted 802.11 Control frames : 4 octets
* Frames that reached max-retry limit : 4 octets
* Transmitted frames with 1 retry attempt : 4 octets
* Transmitted frames with 2 retry attempts : 4 octets
* Transmitted frames with more than 2 retry attempts : 4 octets
* Frames transmitted at each 802.11 PHY rate : 12*4 octets - The
counters indicate the number of frames at each of the following
rates respectively : 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48,
54 Mbps
* Total frame dropped : 4 octets
* Frames dropped due to insufficient resources : 4 octets
* Frames dropped due to power-save timeouts : 4 octets
* Frames dropped due to other reasons : 4 octets
* Fragments Transmitted : 4 octets
* Fragments dropped : 4 octets
* Power-save multicast frames : 4 octets
* Power-save unicast frames : 4 octets
6.1.3.1.32 Received Frame Counters
This information element includes all statistics related to the
reception of the frames by WTP. These counters apply to either a BSS
or an Access Category (if WMM is enabled).
Element ID : 31
Length : 108 octets
Value : The value of this element is defined as follows.
* Total Frames received : 4 octets
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* Frames with the retry bit set : 4 octets
* 802.11 Data frames received : 4 octets
* 802.11 Mgmt frames received : 4 octets
* 802.11 Control frames received : 4 octets
* CRC errors : 4 octets
* PHY errors : 4 octets
* Total Fragments received : 4 octets
* Reassembled frames : 4 octets
* Reassembly failures : 4 octets
* Successful Decryption : 4 octets
* Decryption failures : 4 octets
* Rate statistics : 48 octets - the number of frames received at
each of the 802.11 PHY rates respectively - 1, 2, 5.5, 11, 6,
9, 12, 18, 24, 36, 49, 54 Mbps
* Total frames dropped : 4 octets
* Frames dropped due to insufficient resources : 4 octets
* Frames dropped due to other reasons : 4 octets
6.1.3.1.33 Association Statistics
This element includes information about the current stations
associated with the BSS.
Element ID : 32
Length : Variable
Value : The value is defined as follows.
* Total association requests : 4 octets
* Total associations accepted : 4 octets
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* Total associations rejected : 4 octets
* Current associations : 4 octets
* For each associated station,
+ Station MAC address : 6 octets
+ Power save state : 1 octet
+ Current Tx rate : 1 octet
+ Rate of last packet : 1 octet
+ Preamble type : 1 octet
+ WMM/U-APSD state : ?? octet
6.1.3.1.34 Status Element
The status IE is included in the status response message sent by the
WTP to the AC. It contains a set of fields that are used to indicate
the status of various states at the WTP or each BSS configured in the
WTP.
Element ID : 33
Length : 2 octets
Value : The value is defined as follows.
ERP element, if applicable. If not applicable, then this field
MUST be set to 0
Noise Floor : 1 octet
6.1.3.1.35 Event Configuration
This element is used by the AC to configure the set of events that it
wants to be notified by the WTP.
Element ID : 34
Length : 4 octets
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Value : The value is defined as follows.
* Radar Detection - 1 octet
+ Bit 0 : 1 = notify on detecting radar interference, 0
otherwise
+ Bit 1 : 1 = notify of channel change due to radar
interference, 0 otherwise
+ All other bits are reserved.
* Excessive Retry Event - 1 octet. Number of successive frames
that have not been acknowledged by a client. A value of 0
disables notification.
* Noise Floor Threshold - 1 octet. Defines the threshold above
which an event would be generated by the WTP.
* 802.11 Management and Action Frame Notification - 1 octet.
+ Bit 0 : If set, notify AC of probe requests from stations
(please use with caution). If reset, then no probe response
notification is needed.
+ Bit 1 : If set, the WTP should notify the AC of all other
management frames from stations.
+ All other bits are reserved.
6.1.3.1.36 Radar Detection Event
This element is used by the WTP to notify the AC of detection of
radar interference and any channel changes as a result of this
detection.
Element ID : 35
Length : 10 octets
Value : defined as follows.
BSSID : 6 octets. The BSSID of the WLAN interface that
detected the radar interference.
Channel : 2 octets. The channel on which radar interference
was detected.
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New Channel : 2 octets. The new channel to which the WTP moved
as a result of detection of radar interference.
6.1.3.1.37 Excessive Retry Event
This element is used by the WTP to indicate excessive retry events on
transmission to an associated station.
Element ID : 36
Length : 14 octets
Value : defined as follows.
Station MAC : 6 octets
Associated BSSID : 6 octets
Length of last burst of excessive retries : 2 octets.
6.1.3.1.38 Noise Floor Event
This element is used by the WTP to notify the AC of the current noise
floor at one of the WLAN interfaces exceeding the configured noise
floor threshold.
Element ID : 37
Length : 10 octets
Value : defined as follows.
BSSID : 6 octets
Current Channel : 2 octets
Current Noise Floor : 2 octets
6.1.3.1.39 Raw 802.11 Frame
This element provides a generic capability for either a WTP or an AC
to send a raw 802.11 frame to the other party. For example, it can
be used to notify the AC of station association/disassociation events
in the case of local MAC architectures.
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Element ID : 252
Length : Variable
Value : a raw 802.11 frame
6.1.3.1.40 Vendor-Specific Element
This element is used to transfer vendor-specific information between
the WTP and the AC.
Element ID : 253
Length : Variable, > 3
Value : This variable length element starts with a 3-octet OUI,
followed by a series of octets that are specific to the vendor
represented by the OUI.
6.1.3.1.41 Recursion Element
This element type can be used to recursively define a variable length
element that should be interpreted as a series of other elements
defined in this section. It can be used to bound a set of elements
as a unit.
Element ID : 254
Length : Variable
Value : A variable length element that contains a set of one or
more elements defined in this section.
6.1.3.1.42 Pad Element
This is a generic element type which can be used to pad the packets,
if necessary.
Element ID : 255
Length : Variable
Value : A variable length element that MUST be filled with all 0s
at the source and MUST be ignored at the destination.
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6.1.3.2 SLAPP 802.11 Control Protocol Messages
6.1.3.2.1 Registration Request
At the start of the SLAPP 802.11 control protocol, the WTP sends a
registration request to the AC that it authenticated with. The
registration request carries a list of information elements
indicating the WTP's capabilities to the AC. The message starts with
the SLAPP 802.11 control protocol header (Figure 8) with a SLAPP
control protocol message type of 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transaction ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Elements ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: SLAPP 802.11 Registration Request
Flags : Reserved
Transaction ID : a 32-bit random number chosen by the WTP at the
start of a new registration phase. This number is used in the
registration response by the AC to match the response to the
corresponding request.
The following information elements are mandatory in the capabilities
exchange.
1 : CAPWAP mode
2 : Number of WLAN interfaces
For each WLAN interface:
7 : 802.11 PHY mode and Channel Information
8 : Cryptographic Capability
9 : Other 802.11 standards support
The following information elements may be optionally included in the
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registration request.
For each WLAN interface:
4 : WLAN Interface HW Vendor ID
5 : WLAN Interface Type ID
6 : Regulatory Domain
10 : Antenna Information Element
11 : Number of BSSIDs
253 : Vendor-specific Element
6.1.3.2.2 Registration Response
Upon receiving a registration request, the AC may either chose to
accept 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transaction ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Elements ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: SLAPP 802.11 Registration Response
Flags :
Bit 0 : indicates the status of the transaction, 0 = successful
response from the AC, 1 = the registration request is being
rejected by the AC.
Bits 1-7 : Reserved
Bits 8-15 : If bit 0 = 1 (i.e., the registration request is
being rejected by the AC), then this field contains a reason
code. Otherwise, these bits are currently set to 0. The
following reason codes are currently defined.
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0 : Reserved
1 : Unspecified reason
2 : Unable to handle more WTPs
3 : Incompatible capabilities
4-255 : Reserved
Transaction ID : a 32-bit random number chosen by the WTP at the
start of a new registration phase. This number is used in the
registration response by the AC to match the response to the
corresponding request.
The following information elements are mandatory if the transaction
is successful.
1 : CAPWAP mode - the mode that the AC chooses from among the list
of supported modes sent by the WTP in the registration request.
24 : SLAPP registration ID
6.1.3.2.3 De-registration Request
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: SLAPP 802.11 Deregistration Request
Flags : Reserved
SLAPP Registration ID : The registration ID assigned by the AC
upon successful registration
Reason Code : The following are valid values.
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0 : Unspecified reason
1 : The device that is the source of the frame is going down
All other values are reserved
6.1.3.2.4 De-registration Response
The De-registration response is a simple ACK from the recipient of
the corresponding de-registration request.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: SLAPP 802.11 Deregistration Response
Flags : Reserved
SLAPP Registration ID : The registration ID assigned by the AC
upon successful registration
Reason Code : The same reason code used in the corresponding
request
6.1.3.2.5 Configuration Request
The configuration request message is used by the WTP to request a set
of configuration for each BSS that the AC wishes to configure at the
WTP.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element ID list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: SLAPP 802.11 Configuration Request
The Information Element ID list field contains the list of IEs that
the WTP is interested in obtaining configuration information for.
6.1.3.2.6 Configuration Response
The Configuration response message is used by the AC to respond to a
configuration request by 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: SLAPP 802.11 Configuration Response
The following information elements are mandatory in the configuration
response.
01: CAPWAP mode
For each WLAN interface:
03: WLAN Interface Index
27: Radio Mode
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07: 802.11 PHY mode and Channel Selection
For each BSSID:
12: BSSID Index
13: ESSID
08: Cryptographic Selection
The following information elements may be optionally included in the
configuration response.
10: Antenna Information Element
25: WTP Name
For each WLAN interface:
For each BSSID:
14: ESSID Announcement Policy
15: Beacon Interval
16: DTIM Period
17: Basic Rates
18: Supported rates
19: Retry Count
20: Fragmentation Threshold
21: RTS Threshold
22: Short/Long Preamble
23: 802.1Q Tag
253: Vendor specific element
If any of the optional IEs is absent in the configuration response
message, then their default values are applied by the WTP.
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6.1.3.2.7 Configuration Update
The Configuration Update message is initiated by the AC to push
modified or updated configuration to the WTP. It has a format
similar to that of the configuration response message defined above.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: SLAPP 802.11 Configuration Update
The list of mandatory and optional IEs for the configuration update
message is the same as that for the configuration response message.
6.1.3.2.8 Configuration Acknowledgment
The Configuration Acknowledgment message is used by the WTP to inform
the AC whether it has accepted the prior configuration update or
configuration response message. The WTP can reject the configuration
sent by the AC, in which case it MUST return to the discovery state.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: SLAPP 802.11 Configuration ACK
The Status Code field contains one of the following values:
0 : Success - The WTP accepts that the configuration pushed by the
AC and has applied it.
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1 : Failure - The WTP did not accept the configuration pushed by
the AC and MUST be de-registered at the AC.
6.1.3.2.9 Status Request
The Status request message is used by the AC to request the
configuration and operational status from 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 9 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element ID list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: SLAPP 802.11 Status Request
The Information Element ID list contains the list of IEs that the AC
requests status for.
6.1.3.2.10 Status Response
The Status response message is used by the WTP to respond to a status
request from the AC.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 10 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: SLAPP 802.11 Status Response
The Flags field contains one of the following values:
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Bit 0 : If set, Unknown AC or SLAPP registration ID. If this bit
is reset, then this indicates a successful response.
Bit 1 : If set, WTP indicates that it has not been configured yet,
otherwise the WTP is in a configured state.
All other values are reserved
The Status IE is mandatory in a Status Response message.
6.1.3.2.11 Statistics Request
The Statistics request message is used by the AC to request
statistics information from 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: SLAPP 802.11 Statistics Request
The Flags field contains the following bits:
Bit 0 : If set to 1, then the WTP should reset the counters after
sending the statistics response message.
All other bits are reserved and MUST be set to 0 by the source and
ignored by the destination.
6.1.3.2.12 Statistics Response
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 12 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Information Element list ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 20: SLAPP 802.11 Statistics Response
The Flags field contains the following bits:
Bit 0 : if set then the counters have been reset as requested by
the AC.
Bit 1 : If set, then the WTP has encountered a statistics request
from either an unknown AC or with an unknown SLAPP registration
ID.
Bit 2 : If set, WTP indicates that it has not been configured yet,
otherwise the WTP is in a configured state.
All other bits are reserved.
6.1.3.2.13 Keepalive
The keepalive messages can be initiated by either the WTP or the AC.
It is used to probe the availability of the other party and the path
between them. The initial message is termed the keepalive request,
while the response to that message is termed the keepalive response.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 13 | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 21: SLAPP Keepalive Packet
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The Flags field has the following values:
Bit 0 : Set to 0 in a keepalive request message, set to 1 in a
keepalive response message.
Bit 1 : Set to 0 in a keepalive request message, set to 1 in a
keepalive response message if the initiator of the keepalive
request is unknown or the SLAPP registration ID is incorrect, and
set to 0 otherwise.
All other bits are reserved and must be set to 0 by the source and
ignored at the destination.
6.1.3.2.14 Key Configuration
In CAPWAP mode 5, the 802.11 crypto functions are performed at the
AC. So there is no need for the AC to send PTKs/GTKs to the WTP.
When one of CAPWAP Modes 1-4 has been negotiated between the AC and
WTP it is necessary for the AC to send both unicast and broadcast/
multicast keys to the WTP. This is accomplished after the 802.1x
authenticator (which resides on the AC) has successfully
authenticated the supplicant. Key configuration requests are
differentiated-- unicast or broadcast-- by setting or clearing the
high-order bit of the "Flags" field. The setting of this bit
determine the contents of the Key configuration request following the
SLAPP Registration ID.
6.1.3.2.14.1 Unicast Key Configuration Request
The Unicast Key Configuration Request is used by the AC to inform the
WTP of the key to use when protecting unicast frames to and from a
specified supplicant.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 15 |0| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| supplicant MAC address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| supplicant mac address (cont) | Supp 802.1Q tag | RSVD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| unicast key length | unicast key ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22
Note the high order bit of the "Flags" field is cleared to indicate a
unicast key is being sent. The 802.1Q tag field is used to indicate
to the WTP which VLAN this supplicant is in and which broadcast/
multicast key to use when communicating to it with broadcast/
multicast frames.
6.1.3.2.14.2 Broadcast/Multicast Key Configuration Request
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 15 |1| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 801.1q tag | RSVD | broadcast/multicast key length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ broadcast/multicast key ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23
Note the high-order bit of the "Flags" field is set indicating a
broadcast/multicast key is being sent. The bits marked "RSVD" are
reserved and MUST be set to zero by the AC and ignored by the WTP.
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6.1.3.2.14.3 Unicast Key Configuration Response
The WTP acknowledges receipt of a Unicast Key Configuration Request
by sending a Unicast Key Configuration Response. This response
mirrors the request but does not send back the key length or the key
itself. (The RSVD bits are returned for alignment purposes and MUST
be set to zero by the WTP and ignored by the AC).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16 |0| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| supplicant MAC address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| supplicant mac address (cont) | Supp 802.1Q tag | RSVD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 24
6.1.3.2.14.4 Multicast Key Configuration Response
The WTP acknowledges receipt of a Multicast Key Configuration Request
by sending a Multicast Key Configuration Response. This response
mirrors the request but does not send back the key length or the key
itself. (The RSVD bits are returned for alignment purposes and MUST
be set to zero by the WTP and ignored by the AC).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16 |0| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SLAPP Registration ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 801.1q tag | RSVD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 25
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6.1.3.3 Monitoring and Statistics
An AC may want to periodically monitor the health of a WTP, collect
the necessary information for diagnostics, and get notifications on
pre-defined events at the WTP that may be of interest. This section
defines a set of WTP statistics and events and describes the process
of collecting statistics from WTPs and configuring the event
notification mechanism at the WTP. It is beyond the scope of this
document to describe what should/could be done with the collected
information.
6.1.3.3.1 Statistics Collection Procedure
The simple statistics collection procedure defined here does not
require the WTP to maintain any timers or any similar mechanisms. A
WTP is responsible only for maintaining the statistics defined in
Information Elements 29, 30, 31, and 32. The WTP must also respond
to a statistics request message from the AC by delivering the
appropriate statistics to the AC using a statistics response message.
For example, if an AC is interested in gathering periodic statistics
about some specific statistics, it is the responsibility of the AC to
poll the WTP at the appropriate intervals.
6.1.3.3.2 Events Procedure
The event notification process includes the following: 1) Event
Registration: The registration of events of interest at the WTP by
the AC and 2) Notification: The communication of event-related
information by the WTP to AC whenever the conditions for a specific
registered event has occurred. The set of events supported by a WTP
and the event-specific parameters that may be configured as part of a
event registration are given in Section 6.1.3.3.3.
6.1.3.3.3 WTP Events
This section defines a set of WTP events along with the event-
specific parameters that may be configured by ACs and the event-
related information that should be delivered to the ACs by WTPs when
the conditions for a particular configured event has occurred.
Radar Detection Event: Configure whether the AC is interested in
receiving a notification whenever a radar event is detected. The
WTP may notify the AC about the type of radar interference and the
new channel that the WTP has moved to as a result, if any, using
the Radar Detection Event Element (element ID : 35).
Excessive Retry Event: Configure the number of consecutive
transmission failures before a notification is generated. The WTP
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may notify the MAC address of the STA and the number of
consecutive unacknowledged frames so far using the Excessive Retry
Event Element (element ID : 36).
Noise Floor Event: Configure the noise floor threshold above which
an event notification would be generated by the WTP. The WTP may
notify the AC with the most recent measured noise floor that
exceeded the configured threshold using the Noise Floor Event
Element (element ID : 37).
De-authentication Event: Configure whether the AC is interested in
receiving a notification whenever a station has been de-
authenticated by WTP. The WTP may notify the AC with the MAC
address of the STA along with a reason code (inactivity, etc).
Association Event: Needed in local MAC architecture
Disassociation Event: Needed in local MAC architecture
6.1.4 Protocol Operation
The SLAPP 802.11 control protocol operation is described in this
section.
6.1.4.1 SLAPP 802.11 Control Protocol State Machine
6.1.4.1.1 At the WTP
+-------------+
| discovering |<-------------------------------+<----+
+-------------+ | |
^ ^ | |
| | +-----------+ | |
| | | securing | | |
| | +----+------+ | |
| | | | |
| | v | |
| | +--------------+ | |
| | +--->| Unregistered | | |
| | | +------+-------+ | |
| | | | | |
| | | |Registration | |
| | |Timeout |Request | |
| | | | | |
| | | v | |
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| | | +--------------+ | |
| | +----+ Registration | | |
| | | | | |
| | Reject | | | |
| +--------+ Pending | | |
| nTimeout>3| | | |
| | | | |
| +------+-------+ | |
| | | |
| |Accept | |
| | | |
| | | |
| v | |
| +------+-------+ | |
| | Registered | | |
| +--->| | | |
| | +------+-------+ | |
| | | | |
| |Timeout |Config | |
| | |Request | |
| | | | |
| | v | |
| | +------+-------+ | |
| +----+ | Reject| |
| |Configuration | | |
| Reject | Pending | | |
+-----------+ | | |
^ nTimeout>3+------+-------+ | |
| | | |
| | | |
De-reg| | +----------------+ | |
resp | | v Accept | | |
+----+---+ +------+----+--+ +-+---+--+ |
| | De-reg| | | Update | |
| De +<------+ Configured +-----------+ | |
|Register| req | | | Pending| |
| | | | +----+---+ |
+--------+ +------+-------+ |
| |
| |
| |
Too |Many |
Keepalive |
Failures |
| |
| |
| Deregister |
+-------------------------------+
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In Configured and/or Registered states, respond to
Status Requests, Statistics Requests, Keepalives, Key Config
Figure 26: SLAPP 802.11 Control Protocol at the WTP
6.1.4.1.1.1 State Machine Explanation
Unregistered : The transition into this state is from the securing
state (Figure 3). Send registration request message to move to
Registration Pending state, set timer for registration response.
Registration Pending : On a registration response from AC, cancel
registration timer. If response is successful, move to Registered
state. If not, move to discovering state (Figure 3). If timer
expires, if nTimeout >3, then move to discovering state. If not,
return to Unregistered state.
Registered : Send Configuration request message to AC to move to
Configuration Pending state, and set timer for configuration
response. In this state, respond to status request, statistics
request, and keepalive messages from AC.
Configuration Pending : If configuration response received from AC,
cancel configuration response timer. If response is successful
and the configuration is acceptable, then send Configuration ACK
message to AC, and move to Configured state. If configuration
request is rejected or configuration is not acceptable, then send
a deregister request to AC and move to discovering. If
configuration response timer expires, move to Registered state
unless nTimeout >3, in which case move to discovering state.
Configured : In the Configured state, the WTP responds to Status
request, Statistics Request, and Keepalive messages from the AC.
If it receives a de-register request message from the AC, then it
sends a de-register response to the AC and moves to the
discovering state. If the WTP receives a Configuration Update
message, then it moves to the Update Pending state. If it
receives too many consecutive Keepalive failures (no responses
from the AC to Keepalive requests), then it sends a deregister
message to the AC and moves to the discovering state.
Update Pending : In the Update Pending state, the WTP analyzes the
configuration information received in the Configuration Update
message. If the configuration is found to be acceptable, then it
applies the configuration and returns to the Configured state. If
the WTP chooses to reject the configuration update, then it sends
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a deregister request to the AC and moves to the discovering state.
De-register : From the Configured state, the WTP moves to the De-
register state when it receives a deregister request message from
the AC. It sends a deregister response to the AC and moves to the
discovering state.
6.1.4.1.2 At the AC
+----------+
| securing |
+----+-----+
|
|
|
v
+--------------+
+--------| Unregistered |
| +----+---------+
| |
|Timeout |Register
| |request
| v +-------------+
| +----------+ Accept | Registration|
| +---+Register +----------->| Pending |
| | |Processing| +-+-----+-----+
| | +----------+ | |
| | | |
| |Reject Timeout |
| | | |Config
| | | |Request
| | +--------------+ | |
| +----->| |<------+ |
| | discovering | v
+----------->| | +------------+
+--------------+ | Registered |
^ ^ ^ +----+-------+
| | | |
| | | |Config
| | | |Response
| | | v
| | | Timeout +------------+
| | +----------| Config |
| | or Reject | Pending |
| | +----+-------+
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| | |
| | |Config ACK
| | v
| | Deregister +------------+
| +-------------| |
| or Keepalive | Configured |<--+
| failures | | |
| +----+-------+ |
Reject| | |
or| | |
Timeout +-----------+ |Config |
| | Update | |Update |
+-----| Pending |<-----+ |
+----+------+ |
| Accept |
+-------------------------+
Figure 27: SLAPP 802.11 Control Protocol at the AC
6.1.4.1.2.1 State Machine Explanation
The states "securing" and "discovering" are described in Figure 3.
Unregistered : This state is entered from the securing state
described in Figure 3. In this state, the AC is waiting for a
registration request message from the WTP. Upon receiving the
registration request message, it moves into the Registration
Processing state.
Registration Processing : In this state, the AC must determine if it
can accept the new WTP or not. If the AC decides to accept the
WTP, it must pick a CAPWAP mode to operate in and send a
registration response message with a success code and moves to the
Registration Pending state. If the AC chooses to reject the
current registration request from the WTP, it must send a
registration response with a failure code and move to the
discovering state.
Registration Pending : If the timer expires before a response from
the WTP is received, then the AC destroys the registration state
and moves to the discovering state. If a configuration request
message is received from the WTP, then the AC moves into the
Registered state and processes the configuration request message.
It sends a configuration response message to the WTP with the
appropriate IEs and moves into the Configuration Pending state.
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Configuration Pending : If the timer expires before a response is
received from the WTP, then the AC destroys the current
registration and moves into the discovering state. If a
configuration ACK is received from the WTP, but contains a failure
code, then the AC again destroys the registration state and moves
into the discovering state. If the configuration ACK from the WTP
is successful, then the AC moves to the Configured state.
Configured : In the Configured state, the AC can send status request,
statistics request, keepalive, key configuration messages to the
WTP. Any response to these messages from the WTP that indicates
an unknown SLAPP registration ID or an unknown AC causes the AC to
destroy any registration or configuration state and move to the
discovering state. From the configured state, the AC can send a
configuration update message and move into the Update Pending
state. If it receives a deregister request from the WTP then it
destroys all current registration and configuration state and
moves into the discovering state. If a number of successive
keepalive messages go unacknowledged by the WTP, then the AC moves
into the discovering state.
Update Pending : When the AC receives an configuration ACK message
with a success code, then it returns to the Configured state. If
the status code is a failure or if the timer expires before the
configuration ACK is received from the WTP, the AC destroys all
registaration and configuration state for the WTP and moves into
the discovering state.
6.2 Image Download Protocol
The Image Download protocol is a control protocol defined in this
draft that is generic enough to be agnostic to the underlying
technology.
In the image download protocol, the WTP obtains a bootable image from
the AC by receiving a series of image transfer packets. Missed image
data packets are re-requested by the WTP by sending image data
request packets indicating the missing packets.
The image to download is divided into slices of equal size (except
for the last slice which can be less than the slice size provided it
is also greater than zero). The size of each slice depends on the
MTU determined by the DTLS exchange and SHOULD be the realized MTU
minus the size of an Image Download Request (Figure 29).
Note that the image download packet and download image request is
encapsulated in a DTLS header which secures the image download.
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6.2.1 Image Download Packet
The format of an image download packet is shown in Figure 28.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | Type = 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED |M|R| packet sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ image data slice ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 28: SLAPP Image Download Packet
where:
length: variable
RESERVED: unused in this version of SLAPP, MUST be zero (0) on
transmission and ignored upon receipt
M: the "More" bit indicating that the current packet is not the final
one
R: the "Request" bit. This bit MUST be set to one (1) when the
packet is the response to a request and zero (0) otherwise.
packet sequence number: a monotonically increasing counter which
assigns a unique number to each slice of the image
image data slice: a portion of the bootable image.
6.2.2 Image Download Request
The format of an image download request is show in Figure 29.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maj | Min | Type = 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESERVED |M|R| packet sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 29: SLAPP Image Download Request Packet
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where:
length: eight (8) octets
RESERVED: unused in this version of SLAPP, MUST be zero on
transmission and ignored upon receipt
M: the "More" bit. This MUST be equal to the one (1) when negatively
acknowledging a missed packet and set to zero (0) when indicating
the end of the Image Download protocol.
R: the "Request" bit. This MUST be one in an Image Download Request.
packet sequence number: the packet sequence number of the missing
image data slice.
6.2.3 Image Download Process
The AC will divides the bootable image into a series of slices and
sends each slice as an Image Download packet. The size of each image
data slice (and therefore the size of each image download packet)
depends on the MTU of the connection determined during the DTLS
handshake. With the transmission of each slice the AC MUST increment
the packet sequence number.
Image Download packets are negatively ack'd. An AC MUST NOT assume
anything about the reception of packets it sends based upon negative
acks. One could naively assume that since the packets are sent
sequentially that all packets with a sequence number of "n - 1" are
implicitly ack'd by the receipt of a request for the packet with
sequence number "n" to be retransmitted. Such an assumption would be
incorrect since previous requests could, themselves, have been
dropped.
The image download process is initiated by the WTP requesting a
packet with the packet sequence number of zero (0). The AC sets the
packet sequence counter for this WTP to one (1) and sends the first
slice. The "Request" bit for the first slice sent by the AC MUST be
set to zero (0) since the first slice was technically not requested.
The WTP sets a periodic timer that, when it fires, causes the WTP to
sends Image Download requests for slices that have been missed since
the last periodic timer had fired. Since individual Image Download
packets are not ack'd the AC MUST NOT set a timer when each one is
sent.
If a WTP notices missed image transfer packets-- when the difference
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between the packet sequence number of a received image transfer
packet and the packet sequence number of the last image transfer
packet previously received is greater than one-- it will note that
fact in a bitmask. When the periodic timer fires the WTP will
request the slices that are absent from that bitmask. Each slice
will be requested by sending a Download Request with a length of
eight (8) and indicating the sequence number of the packet requested.
The AC MUST interleave these retransmissions with packets in the
sequence.
Since both sides implicitly agree upon the MTU of the link the WTP
will know the slice size that the AC will use during the Image
Download process. A dropped packet will therefore result in an
internal buffer pointer on the WTP being incremented by the slice
size and the lost packet requested. When the lost packet is received
it can be inserted into the buffer in the space provided by the
pointer increment when its loss was first detected. That is, loss of
packet <n> will result in packet <n> being re-requested and when
received inserted into the buffer at an offset of <n-1> * <slicesize>
from the start of the buffer.
The final packet sent by the AC will not have the "more" bit set and
this indicates to the WTP that the end of the image has been
received. This final packet is acknowledged by the WTP indicating
the end of the Image Download process.
A lost final packet will result in the AC resending the final packet
again (see Section 4.4).
6.2.4 Image Download State Machine
The Image Download protocol is a negotiated control protocol defined
for SLAPP. Transitions to it come from the "secure" state and
transitions out of it go to "acquire". See Figure 3.
6.2.4.1 AC
The AC's state machine for the Image Download protocol is shown in
Figure 30. The AC maintains the following variables for its state
machine:
seq_num: the current slice that is being sent
nslices: the total number of slices in the image
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req_num: the number of the slice that was requested
more: whether the "More bit" in the packet should be set
starved: a timer which sets the maximum amount of time in which an AC
will attempt to download an image.
Note: the symbol "C" indicates an event in a state which results in
the state remaining the same.
|
v
+----------+
| waiting |
+----------+
|
| seq_num = 1, more = 1,
| nslices = x, starved = t
M bit v
+----------+ is 0 +-------------+
| finished |<-------| received |<------\
+----------+ | |<----\ |
+-------------+ | |
req_num = requested | | |
packet | M bit is 1 | |
V | |
+----------+ | |
seq_num++, C| sending |------/ |
req_num=0 +----------+ |
| |
| | |
+-------------+ | | |
| discovering |<----/ | |
| |<----\ | |
+-------------+ | | |
| v v
+--------+ |
| idle |---------/
+--------+
Figure 30: SLAPP Image Download Protocol State Machine at the AC
The following states are defined:
Waiting: When the AC leaves the SLAPP state of "Secure" it enters the
"Waiting" state of the Image Download protocol. seq_num is set to
one (1), more is set to one (1), and nslices is set to the number
of slices in the particular image to download, and starved is set
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to the maximum amount of time the AC will devote to downloading a
particular image.
Received: The AC enters this state when it has received an Image
Download request. If the sequence number of the packet is zero
(0) it sets seq_num to one (1) and transitions to Sending, else if
the M bit is set it sets req_num to the sequence number of the
request and transitions to Sending else (if the M bit is clear) it
transitions to Finished.
Sending: The AC is sending a slice to the WTP. If req_num is equal
to zero (0) it sends the slice indicated by seq_num and increments
seq_num. If req_num is greater than zero (0) it sends the slice
indicated by req_num and sets req_num to zero (0). The "More" bit
in either case is set depending on the value of more. As long as
no request packets are received Sending transitions to Sending.
When seq_num equals nslices "More" is set to zero (0) and the
state transitions to Idle. If the starved timer expires the AC
transitions to the SLAPP state of Discovering.
Idle: The AC has sent all the slices in the image and is just waiting
for requests. If the starved timer expires the AC transitions to
the SLAPP state of Discovering.
Finished: The Image Download protocol has terminated. The starved
timer is canceled.
6.2.4.2 WTP
The WTP's state machine for the Image Download protocol is shown in
Figure 31. The WTP maintains the following variables for its state
machine:
recv_num: the sequence number of the last received slice
req: a bitmask whose length equals the number of slices in the image
retry: a timer
giveup: a timer
final: the sequence number of the last slice
Note: the symbol "C" indicates an event in a state which results in
the state remaining the same.
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|
v
+----------+
| init | recv_num = 0,
+----------+ final = 0, req = 0,
| giveup = t
v
+----------+ +-----------+
| finished |<------- | sending |<-------\
+----------+ +-----------+ |
| | retry fires
v |
+--------------+ |
bit in req = C| receiving |------/
seq_num in packet +--------------+
is set |
| giveup fires
v
+-------------+
| discovering |
+-------------+
Figure 31: SLAPP Image Download Protocol State Machine at the WTP
The following states are defined:
Init:
When the WTP leaves the SLAPP state of "Secure" it enters the
"Init" state of the Image Download Protocol. recv_num, final, and
the req bitmask are set to zero (0), and the giveup timer is set
to a suitably large number. The WTP transitions directly to
Sending.
Sending:
If recv_num is zero (0) the WTP sends a request for a packet with
sequence number of zero (0) and the "More" bit set to one (1).
Otherwise for every unset bit in req between one (1) and recv_num
a request packet is sent with the sequence number corresponding to
the unset bit in req and the "More" bit set to more.
If there are no unset bits in req and final is non-zero a request
packet is sent for the sequence number represented by final with
the "More" bit cleared, giveup is cleared and the state machine
transitions to Finished. Otherwise retry is set to a suitable
value and the WTP transitions to Receiving.
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Receiving:
In this state the WTP receives Image Download packets. The bit in
req corresponding to the sequence number in the received packet
is set indicating this packet has been received. If the sequence
number of the received packet has already been received the packet
is silently dropped, otherwise the data in the packet is stored as
the indicated slice in a file which represents the downloaded
image. If the received packet has the "More" bit cleared final is
set to the sequence number in that packet. When the retry timer
fires the WTP transitions to Sending. If the giveup timer fires
the WTP transitions to the SLAPP state of Discovering.
Finished:
The image download protocol has finished.
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7. Security Considerations
This document describes a protocol, SLAPP, which uses a different
protocol, DTLS, to provide for authentication, key exchange, and bulk
data encryption of a negotiated control protocol. It's security
considerations are therefore those of DTLS.
The AC creates state upon receipt of an acceptable Discovery Request.
AC implementations of SLAPP SHOULD therefore take measures to protect
themselves from denial of service attacks which attempt to exhaust
resources on target machines. These measures could take the form of
randomly dropping connections when the number of open connections
reaches a certain threshold.
The WTP exposes information about itself during the discovery phase.
Some of this information could not be gleaned by other means.
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8. Extensibility to other technologies
The SLAPP protocol can be considered to be a technology-independent
protocol that can be extended with technology-specific components to
solve an interoperability problem where a central controller from one
vendor is expected to control and manage network elements from a
different vendor.
While the description of the SLAPP protocol in this draft assumes
that it is meant to solve the multi-vendor interoperability problem
as defined in the CAPWAP problem statement [3], splitting the
solution to two components where technology-dependent control
protocols are negotiated using a technology-independent framework
enables the use of SLAPP as the common framework for multiple
underlying technologies that are vastly different from one another.
9. References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", March 1997, <ftp://ftp.isi.edu/in-notes/rfc2119>.
[2] "Architecture Taxonomy for Control and Provisioning of Wireless
Access Points(CAPWAP)", August 2004, <ftp://ftp.isi.edu/
internet-drafts/draft-ietf-capwap-arch-06.txt>.
[3] "Configuration and Provisioning for Wireless Access Points
(CAPWAP) Problem Statement", February 2005,
<http://www.ietf.org/rfc/rfc3990.txt>.
[4] "Generic Routing Encapsulation", March 2000,
<http://www.ietf.org/rfc/rfc2784.txt>.
[5] "Requirements for Internet Hosts - Communication Layers",
October 1989, <http://www.ietf.org/rfc/rfc1122.txt>.
[6] Govindan, S., "Objectives for Control and Provisioning of
Wireless Access Points (CAPWAP)", November 2004, <http://
www.ietf.org/internet-drafts/
draft-ietf-capwap-objectives-00.txt>.
[7] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", February 2004, <http://www.ietf.org/internet-drafts/
draft-rescorla-dtls-03.txt>.
[8] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999,
<ftp://ftp.isi.edu/in-notes/rfc2246.txt>.
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[9] Modadugu, N. and E. Rescorla, "The Design and Implementation of
Datagram TLS",
<http://crypto.stanford.edu/~nagendra/papers/dtls.pdf>.
[10] Krishna, P. and D. Husak, "Simple Lightweight RFID Reader
Protocol", March 2005, <http://www.ietf.org/internet-drafts/
draft-krishna-slrrp-01.txt>.
Authors' Addresses
Partha Narasimhan
Aruba Networks
1322 Crossman Ave
Sunnyvale, CA 94089
Phone: +1 408-480-4716
Email: partha@arubanetworks.com
Dan Harkins
Trapeze Networks
5753 W. Las Positas Blvd
Pleasanton, CA 94588
Phone: +1-925-474-2212
Email: dharkins@trpz.com
Subbu Ponnuswamy
Aruba Networks
1322 Crossman Ave
Sunnyvale, CA 94089
Phone: +1 408-754-1213
Email: subbu@arubanetworks.com
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