faqs.org - Internet FAQ Archives

RFC 5413 - SLAPP: Secure Light Access Point Protocol


Or Display the document by number




Independent Submission                                     P. Narasimhan
Request for Comments: 5413                                    D. Harkins
Category: Historic                                         S. Ponnuswamy
ISSN: 2070-1721                                           Aruba Networks
                                                           February 2010

               SLAPP: Secure Light Access Point Protocol

Abstract

   The Control and Provisioning of Wireless Access Points (CAPWAP)
   problem statement 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
   between the two classes of devices (WTPs and ACs) that then enables
   an AC from one vendor to control and manage a WTP from another.

   In this document, 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, more generic image download protocol, in this
   document.

   Even though the text in this document is written to specifically
   address the problem stated in RFC 3990, 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).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for the historical record.

   This document defines a Historic Document for the Internet community.
   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5413.

IESG Note

   This RFC documents the SLAPP protocol as it was when submitted to the
   IETF as a basis for further work in the CAPWAP Working Group, and
   therefore it may resemble the CAPWAP protocol specification in RFC
   5415 as well as other IETF work.  This RFC is being published solely
   for the historical record.  The protocol described in this RFC has
   not been thoroughly reviewed and may contain errors and omissions.

   RFC 5415 documents the standards track solution for the CAPWAP
   Working Group and obsoletes any and all mechanisms defined in this
   RFC.  This RFC is not a candidate for any level of Internet Standard
   and should not be used as a basis for any sort of Internet
   deployment.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http//:trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1. Introduction ....................................................4
   2. Definitions .....................................................7
      2.1. Conventions Used in This Document ..........................7
   3. Topology ........................................................7
   4. Protocol ........................................................8
      4.1. Protocol Description .......................................8
           4.1.1. State Machine Explanation ...........................9
      4.2. Format of a SLAPP Header ..................................10
      4.3. Version ...................................................11
      4.4. Retransmission ............................................12
      4.5. Discovery .................................................12
           4.5.1. SLAPP Discover Request .............................13
           4.5.2. SLAPP Discover Response ............................15
      4.6. SLAPP Discovery Process ...................................17
           4.6.1. WTP ................................................17
           4.6.2. AC .................................................19
   5. Security Association ...........................................19
      5.1. Example Authentication Models (Informative) ...............20
           5.1.1. Mutual Authentication ..............................20
           5.1.2. WTP-Only Authentication ............................21
           5.1.3. Anonymous Authentication ...........................21
   6. SLAPP Control Protocols ........................................21
      6.1. 802.11 Control Protocol for SLAPP .........................21
           6.1.1. Supported CAPWAP Architectures .....................21
           6.1.2. Transport ..........................................24
           6.1.3. Provisioning and Configuration of WTP ..............26
           6.1.4. Protocol Operation .................................60
      6.2. Image Download Protocol ...................................66
           6.2.1. Image Download Packet ..............................66
           6.2.2. Image Download Request .............................67
           6.2.3. Image Download Process .............................68
           6.2.4. Image Download State Machine .......................69
   7. Security Considerations ........................................73
   8. Extensibility to Other Technologies ............................73
   9. Informative References .........................................74

1.  Introduction

   The need for a protocol by which wireless LAN (WLAN) Access
   Controllers (ACs) can control and manage Wireless Termination Points
   (WTPs) 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 Medium Access Control (MAC) versus
   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 to 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 in the future.

   In this document, 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 technology-specific components of the control and provisioning
   protocol.  We have also presented two control protocols in this
   document -- 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
   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 document, a SLAPP
   implementation MUST NOT assume that this control protocol is
   supported by other SLAPP implementations.

                                              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 Radio Frequency Identification (RFID) space that has
   led to the definition of a simple lightweight RFID reader protocol
   (SLRRP) [9].  It is quite possible that SLRRP could be a
   technology-specific (RFID, in this case) control protocol negotiated
   during a common technology-independent framework.

   All of the text in the document would seem to be written with a WLAN
   problem in mind.  Please note that while the letter of the document
   does position the solution to solve a CAPWAP-specific problem, the
   spirit of the document is to address the more general problem.

2.  Definitions

2.1.  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].

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 Ethernet, 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 Layer 2 (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.

               +-----------------+            +-------+
               |                 |    (1)     |       |
               |       AC        +------------+  WTP  |
               |                 |            |       |
               +--------+--------+            +-------+
                        |
                        |
                        |
                    +---+---+
               (2)  |       |
             +------+  L2   +--------+
             |      |       |        |
             |      +---+---+        |
             |                       |
             |                       |
       +-----+-----+             +---+---+    +-------+
       |           |             |       | (3)|       |
       |    WTP    |             |   L3  +----+  WTP  |
       |           |             |       |    |       |
       +-----------+             +---+---+    +-------+
                                     |
                                     |
                                     |
                                 +---+----+    +-------+
                                 |        | (4)|       |
                                 |Internet+----+  WTP  |
                                 |        |    |       |
                                 +--------+    +-------+

                           Figure 2: SLAPP Topology

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 that sets the maximum amount of time the WTP will
      wait for an acquired AC to begin the Datagram Transport Layer
      Security (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 that results in the state
   remaining the same.

   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 Discover 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 Discover 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 the 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 6.2.

     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 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
      -----                   ------
      discover request           1
      discover 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
   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.  However, there
   may be valid reasons for which a peer wishes to drop a SLAPP message
   with a supported major version.

   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 that the
   peer supports and not include any incremental capabilities that were
   added that 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.

   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.

    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 re-use 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
   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 Structure of Management
   Information (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 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.

      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.

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 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 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 that 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

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
       Fully-Qualified Domain Name (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.

   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 address
           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 address
           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

                                 Figure 7

4.6.2.  AC

   When an AC receives a SLAPP discover request, it must determine
   whether or not it wishes to acquire the WTP.  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.

5.  Security Association

   Once an AC has been discovered by a WTP and agreed to acquire it (by
   sending a Discover Response), it will initiate a DTLS [6] [8]
   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 [7] 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.

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 that 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 that can uniquely identify it
   (for example, using a certificate) and, that keypair is used in a
   "server-side authentication" [7] 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.

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 components that will
   be used by an AC to control and manage 802.11 WTPs.

6.1.1.  Supported 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 or
      not the AC is also capable of this function.  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
      or not these functions are also available at the WTP.  The WTP
      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, and 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 to which the WTP is
   attached.  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 in
   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:

   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 Traffic Indication Map (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

      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 "Negotiated 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

   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-Extended Service
   Set Identifier (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,
   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 Basic Service Set Identifiers
   (BSSIDs) to the primary interface and to the virtual access point
   (AP) interfaces, if supported, are outside the scope of this
   document.

6.1.3.1.  Information Elements

   Information elements (IEs) 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

      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 WLANs 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

      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 a
   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 Physical Layer (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

      PHY mode : With a length of 1 octet with 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

         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
   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)

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

      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

         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

         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 Request to Send (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.

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 transferred 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

      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

         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

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 Wireless Multimedia (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

      *  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

      *  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

      *  Cyclic Redundancy Check (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

      *  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 : 1 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:

         Enterprise Resource Planning (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

      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 the 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 the 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.

         New Channel : 2 octets.  The new channel to which the WTP moved
         as a result of the 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.

      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
      Organizationally Unique Identifier (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 that 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.

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
   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 or reject its 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              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               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:

            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 De-Registration Request

      Flags : Reserved

      SLAPP Registration ID : The registration ID assigned by the AC
      upon successful registration.

      Reason Code : The following are valid values:

         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 De-Registration 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 configurations for each BSS that the AC wishes to configure at 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              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               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

         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.

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.

      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 for which
   the AC requests status.

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:

      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, the 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

    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

   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 the 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
   determines 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.

    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: Unicast Key Configuration Request

   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: Group Key Configuration Request

   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.

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: Unicast Key Configuration Response

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 it 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: Group Key Configuration Response

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 the 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 have 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
      may notify the MAC address of the station (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 the 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                         |     |
         |  |   |    +--------------+                 |     |
         |  |   +----+ 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                            |
                            |                               |
                            |                               |
                            |   De-Register                 |
                            +-------------------------------+

   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 the AC, cancel
      registration timer.  If the 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 the AC.

   Configuration Pending: If a Configuration Response is received from
      the AC, cancel the Configuration Response timer.  If the response
      is successful and the configuration is acceptable, then send the
      Configuration ACK message to AC, and move to Configured state.  If

      the Configuration Request is rejected or the configuration is not
      acceptable, then send a de-register request to the AC and move to
      discovering.  If the 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 the 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 de-register
      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
      a de-register 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 de-register request message
      from the AC.  It sends a de-register 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    |
                    |     |             +----+-------+
                    |     |                  |
                    |     |                  |Config ACK
                    |     |                  v
                    |     |De-Register  +------------+
                    |     +-------------|            |
                    |     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 whether
      or not it can accept the new WTP.  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.

   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 a status
      request, statistics request, keepalive, and 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 de-register 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 a 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
      registration 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
   document 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 Image Download Request is
   encapsulated in a DTLS header that secures the image download.

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 that
      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 shown 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

   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 divide the bootable image into a series of slices and
   send 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
   send 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
   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 the "acquire" state.  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.

   req_num: The number of the slice that was requested.

   more: Whether the "More bit" in the packet should be set.

   starved: A timer that 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 that 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), nslices is set to the
      number of slices in the particular image to download, and starved
      is set 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 that results in
   the state remaining the same.

                               |
                               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.

   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 that 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.

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.  Its security
   considerations are therefore those of DTLS.

   The AC creates state upon receipt of an acceptable Discover Request.
   AC implementations of SLAPP SHOULD therefore take measures to protect
   themselves from denial-of-service attacks that 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.

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 document 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.  Informative References

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

   [2]   Yang, L., Zerfos, P., and E. Sadot, "Architecture Taxonomy for
         Control and Provisioning of Wireless Access Points (CAPWAP)",
         RFC 4118, June 2005.

   [3]   O'Hara, B., Calhoun, P., and J. Kempf, "Configuration and
         Provisioning for Wireless Access Points (CAPWAP) Problem
         Statement", RFC 3990, February 2005.

   [4]   Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
         "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.

   [5]   Braden, R., Ed., "Requirements for Internet Hosts -
         Communication Layers", STD 3, RFC 1122, October 1989.

   [6]   Rescorla, E. and N. Modadugu, "Datagram Transport Layer
         Security", RFC 4347, April 2006.

   [7]   Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.2", RFC 5246, August 2008.

   [8]   Modadugu, N. and E. Rescorla, "The Design and Implementation of
         Datagram TLS",
         <http://crypto.stanford.edu/~nagendra/papers/dtls.pdf>.

   [9]   Krishna, P. and D. Husak, "Simple Lightweight RFID Reader
         Protocol", Work in Progress, August 2005.

Authors' Addresses

   Partha Narasimhan
   Aruba Networks
   1322 Crossman Ave
   Sunnyvale, CA  94089

   Phone: +1 408-480-4716
   EMail: partha@arubanetworks.com

   Dan Harkins
   Aruba Networks
   1322 Crossman Ave
   Sunnyvale, CA  94089

   EMail: dharkins@arubanetworks.com

   Subbu Ponnuswamy
   Aruba Networks
   1322 Crossman Ave
   Sunnyvale, CA  94089

   Phone: +1 408-754-1213
   EMail: subbu@arubanetworks.com

 

User Contributions:

Comment about this RFC, ask questions, or add new information about this topic:

CAPTCHA