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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 5415

Network Working Group                                 P. Calhoun, Editor
Internet-Draft                                       Cisco Systems, Inc.
Expires: August 24, 2008                           M. Montemurro, Editor
                                                      Research In Motion
                                                      D. Stanley, Editor
                                                          Aruba Networks
                                                       February 21, 2008


                     CAPWAP Protocol Specification
              draft-ietf-capwap-protocol-specification-09

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on August 24, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).











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Abstract

   This specification defines the Control And Provisioning of Wireless
   Access Points (CAPWAP) Protocol.  The CAPWAP protocol meets the IETF
   CAPWAP working group protocol requirements.  The CAPWAP protocol is
   designed to be flexible, allowing it to be used for a variety of
   wireless technologies.  This document describes the base CAPWAP
   protocol.  The CAPWAP protocol binding which defines extensions for
   use with the IEEE 802.11 wireless LAN protocol is available in [16].
   Extensions are expected to be defined to enable use of the CAPWAP
   protocol with additional wireless technologies.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.1.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     1.2.  Conventions used in this document . . . . . . . . . . . .   8
     1.3.  Contributing Authors  . . . . . . . . . . . . . . . . . .   9
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .  10
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  12
     2.1.  Wireless Binding Definition . . . . . . . . . . . . . . .  13
     2.2.  CAPWAP Session Establishment Overview . . . . . . . . . .  14
     2.3.  CAPWAP State Machine Definition . . . . . . . . . . . . .  16
       2.3.1.  CAPWAP Protocol State Transitions . . . . . . . . . .  18
       2.3.2.  CAPWAP/DTLS Interface . . . . . . . . . . . . . . . .  31
     2.4.  Use of DTLS in the CAPWAP Protocol  . . . . . . . . . . .  33
       2.4.1.  DTLS Handshake Processing . . . . . . . . . . . . . .  33
       2.4.2.  DTLS Session Establishment  . . . . . . . . . . . . .  34
       2.4.3.  DTLS Error Handling . . . . . . . . . . . . . . . . .  35
       2.4.4.  DTLS EndPoint Authentication and Authorization  . . .  36
   3.  CAPWAP Transport  . . . . . . . . . . . . . . . . . . . . . .  40
     3.1.  UDP Transport . . . . . . . . . . . . . . . . . . . . . .  40
     3.2.  UDP-Lite Transport  . . . . . . . . . . . . . . . . . . .  40
     3.3.  AC Discovery  . . . . . . . . . . . . . . . . . . . . . .  41
     3.4.  Fragmentation/Reassembly  . . . . . . . . . . . . . . . .  42
     3.5.  MTU Discovery . . . . . . . . . . . . . . . . . . . . . .  42
   4.  CAPWAP Packet Formats . . . . . . . . . . . . . . . . . . . .  43
     4.1.  CAPWAP Preamble . . . . . . . . . . . . . . . . . . . . .  45
     4.2.  CAPWAP DTLS Header  . . . . . . . . . . . . . . . . . . .  45
     4.3.  CAPWAP Header . . . . . . . . . . . . . . . . . . . . . .  46
     4.4.  CAPWAP Data Messages  . . . . . . . . . . . . . . . . . .  49
       4.4.1.  CAPWAP Data Keepalive . . . . . . . . . . . . . . . .  49
       4.4.2.  Data Payload  . . . . . . . . . . . . . . . . . . . .  50
       4.4.3.  Establishment of a DTLS Data Channel  . . . . . . . .  51
     4.5.  CAPWAP Control Messages . . . . . . . . . . . . . . . . .  51
       4.5.1.  Control Message Format  . . . . . . . . . . . . . . .  52
       4.5.2.  Control Message Quality of Service  . . . . . . . . .  55



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       4.5.3.  Retransmissions . . . . . . . . . . . . . . . . . . .  55
     4.6.  CAPWAP Protocol Message Elements  . . . . . . . . . . . .  56
       4.6.1.  AC Descriptor . . . . . . . . . . . . . . . . . . . .  58
       4.6.2.  AC IPv4 List  . . . . . . . . . . . . . . . . . . . .  60
       4.6.3.  AC IPv6 List  . . . . . . . . . . . . . . . . . . . .  61
       4.6.4.  AC Name . . . . . . . . . . . . . . . . . . . . . . .  61
       4.6.5.  AC Name with Index  . . . . . . . . . . . . . . . . .  62
       4.6.6.  AC Timestamp  . . . . . . . . . . . . . . . . . . . .  62
       4.6.7.  Add MAC ACL Entry . . . . . . . . . . . . . . . . . .  63
       4.6.8.  Add Station . . . . . . . . . . . . . . . . . . . . .  63
       4.6.9.  Add Static MAC ACL Entry  . . . . . . . . . . . . . .  64
       4.6.10. CAPWAP Control IPv4 Address . . . . . . . . . . . . .  64
       4.6.11. CAPWAP Control IPv6 Address . . . . . . . . . . . . .  65
       4.6.12. CAPWAP Local IPv4 Address . . . . . . . . . . . . . .  66
       4.6.13. CAPWAP Local IPv6 Address . . . . . . . . . . . . . .  66
       4.6.14. CAPWAP Timers . . . . . . . . . . . . . . . . . . . .  67
       4.6.15. CAPWAP Transport Protocol . . . . . . . . . . . . . .  67
       4.6.16. Data Transfer Data  . . . . . . . . . . . . . . . . .  68
       4.6.17. Data Transfer Mode  . . . . . . . . . . . . . . . . .  69
       4.6.18. Decryption Error Report . . . . . . . . . . . . . . .  69
       4.6.19. Decryption Error Report Period  . . . . . . . . . . .  70
       4.6.20. Delete MAC ACL Entry  . . . . . . . . . . . . . . . .  70
       4.6.21. Delete Station  . . . . . . . . . . . . . . . . . . .  71
       4.6.22. Delete Static MAC ACL Entry . . . . . . . . . . . . .  71
       4.6.23. Discovery Type  . . . . . . . . . . . . . . . . . . .  72
       4.6.24. Duplicate IPv4 Address  . . . . . . . . . . . . . . .  73
       4.6.25. Duplicate IPv6 Address  . . . . . . . . . . . . . . .  73
       4.6.26. Idle Timeout  . . . . . . . . . . . . . . . . . . . .  74
       4.6.27. Image Data  . . . . . . . . . . . . . . . . . . . . .  75
       4.6.28. Image Identifier  . . . . . . . . . . . . . . . . . .  75
       4.6.29. Image Information . . . . . . . . . . . . . . . . . .  76
       4.6.30. Initiate Download . . . . . . . . . . . . . . . . . .  77
       4.6.31. Location Data . . . . . . . . . . . . . . . . . . . .  77
       4.6.32. Maximum Message Length  . . . . . . . . . . . . . . .  77
       4.6.33. Radio Administrative State  . . . . . . . . . . . . .  78
       4.6.34. Radio Operational State . . . . . . . . . . . . . . .  78
       4.6.35. Result Code . . . . . . . . . . . . . . . . . . . . .  79
       4.6.36. Returned Message Element  . . . . . . . . . . . . . .  81
       4.6.37. Session ID  . . . . . . . . . . . . . . . . . . . . .  81
       4.6.38. Statistics Timer  . . . . . . . . . . . . . . . . . .  82
       4.6.39. Vendor Specific Payload . . . . . . . . . . . . . . .  82
       4.6.40. WTP Board Data  . . . . . . . . . . . . . . . . . . .  83
       4.6.41. WTP Descriptor  . . . . . . . . . . . . . . . . . . .  84
       4.6.42. WTP Fallback  . . . . . . . . . . . . . . . . . . . .  85
       4.6.43. WTP Frame Tunnel Mode . . . . . . . . . . . . . . . .  86
       4.6.44. WTP IPv4 IP Address . . . . . . . . . . . . . . . . .  87
       4.6.45. WTP IPv6 IP Address . . . . . . . . . . . . . . . . .  87
       4.6.46. WTP MAC Type  . . . . . . . . . . . . . . . . . . . .  88



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       4.6.47. WTP Name  . . . . . . . . . . . . . . . . . . . . . .  89
       4.6.48. WTP Operational Statistics  . . . . . . . . . . . . .  89
       4.6.49. WTP Radio Statistics  . . . . . . . . . . . . . . . .  90
       4.6.50. WTP Reboot Statistics . . . . . . . . . . . . . . . .  91
       4.6.51. WTP Static IP Address Information . . . . . . . . . .  92
     4.7.  CAPWAP Protocol Timers  . . . . . . . . . . . . . . . . .  93
       4.7.1.  ChangeStatePendingTimer . . . . . . . . . . . . . . .  93
       4.7.2.  DataChannelKeepAlive  . . . . . . . . . . . . . . . .  93
       4.7.3.  DataChannelDeadInterval . . . . . . . . . . . . . . .  94
       4.7.4.  DataCheckTimer  . . . . . . . . . . . . . . . . . . .  94
       4.7.5.  DiscoveryInterval . . . . . . . . . . . . . . . . . .  94
       4.7.6.  DTLSSessionDelete . . . . . . . . . . . . . . . . . .  94
       4.7.7.  EchoInterval  . . . . . . . . . . . . . . . . . . . .  94
       4.7.8.  ImageDataStartTimer . . . . . . . . . . . . . . . . .  94
       4.7.9.  MaxDiscoveryInterval  . . . . . . . . . . . . . . . .  95
       4.7.10. MaxFailedDTLSSessionRetry . . . . . . . . . . . . . .  95
       4.7.11. ResponseTimeout . . . . . . . . . . . . . . . . . . .  95
       4.7.12. RetransmitInterval  . . . . . . . . . . . . . . . . .  95
       4.7.13. SilentInterval  . . . . . . . . . . . . . . . . . . .  95
       4.7.14. StatisticsTimer . . . . . . . . . . . . . . . . . . .  95
       4.7.15. WaitDTLS  . . . . . . . . . . . . . . . . . . . . . .  95
       4.7.16. WaitJoin  . . . . . . . . . . . . . . . . . . . . . .  96
     4.8.  CAPWAP Protocol Variables . . . . . . . . . . . . . . . .  96
       4.8.1.  AdminState  . . . . . . . . . . . . . . . . . . . . .  96
       4.8.2.  DiscoveryCount  . . . . . . . . . . . . . . . . . . .  96
       4.8.3.  FailedDTLSAuthFailCount . . . . . . . . . . . . . . .  96
       4.8.4.  FailedDTLSSessionCount  . . . . . . . . . . . . . . .  96
       4.8.5.  IdleTimeout . . . . . . . . . . . . . . . . . . . . .  96
       4.8.6.  MaxDiscoveries  . . . . . . . . . . . . . . . . . . .  96
       4.8.7.  MaxRetransmit . . . . . . . . . . . . . . . . . . . .  97
       4.8.8.  ReportInterval  . . . . . . . . . . . . . . . . . . .  97
       4.8.9.  RetransmitCount . . . . . . . . . . . . . . . . . . .  97
       4.8.10. WTPFallBack . . . . . . . . . . . . . . . . . . . . .  97
     4.9.  WTP Saved Variables . . . . . . . . . . . . . . . . . . .  97
       4.9.1.  AdminRebootCount  . . . . . . . . . . . . . . . . . .  97
       4.9.2.  FrameEncapType  . . . . . . . . . . . . . . . . . . .  97
       4.9.3.  LastRebootReason  . . . . . . . . . . . . . . . . . .  97
       4.9.4.  MacType . . . . . . . . . . . . . . . . . . . . . . .  97
       4.9.5.  PreferredACs  . . . . . . . . . . . . . . . . . . . .  98
       4.9.6.  RebootCount . . . . . . . . . . . . . . . . . . . . .  98
       4.9.7.  Static ACL Table  . . . . . . . . . . . . . . . . . .  98
       4.9.8.  Static IP Address . . . . . . . . . . . . . . . . . .  98
       4.9.9.  WTPLinkFailureCount . . . . . . . . . . . . . . . . .  98
       4.9.10. WTPLocation . . . . . . . . . . . . . . . . . . . . .  98
       4.9.11. WTPName . . . . . . . . . . . . . . . . . . . . . . .  98
   5.  CAPWAP Discovery Operations . . . . . . . . . . . . . . . . .  99
     5.1.  Discovery Request Message . . . . . . . . . . . . . . . .  99
     5.2.  Discovery Response Message  . . . . . . . . . . . . . . . 100



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     5.3.  Primary Discovery Request Message . . . . . . . . . . . . 101
     5.4.  Primary Discovery Response  . . . . . . . . . . . . . . . 102
   6.  CAPWAP Join Operations  . . . . . . . . . . . . . . . . . . . 104
     6.1.  Join Request  . . . . . . . . . . . . . . . . . . . . . . 104
     6.2.  Join Response . . . . . . . . . . . . . . . . . . . . . . 105
   7.  Control Channel Management  . . . . . . . . . . . . . . . . . 108
     7.1.  Echo Request  . . . . . . . . . . . . . . . . . . . . . . 108
     7.2.  Echo Response . . . . . . . . . . . . . . . . . . . . . . 108
   8.  WTP Configuration Management  . . . . . . . . . . . . . . . . 110
     8.1.  Configuration Consistency . . . . . . . . . . . . . . . . 110
       8.1.1.  Configuration Flexibility . . . . . . . . . . . . . . 111
     8.2.  Configuration Status  . . . . . . . . . . . . . . . . . . 111
     8.3.  Configuration Status Response . . . . . . . . . . . . . . 112
     8.4.  Configuration Update Request  . . . . . . . . . . . . . . 113
     8.5.  Configuration Update Response . . . . . . . . . . . . . . 114
     8.6.  Change State Event Request  . . . . . . . . . . . . . . . 114
     8.7.  Change State Event Response . . . . . . . . . . . . . . . 116
     8.8.  Clear Configuration Request . . . . . . . . . . . . . . . 116
     8.9.  Clear Configuration Response  . . . . . . . . . . . . . . 116
   9.  Device Management Operations  . . . . . . . . . . . . . . . . 118
     9.1.  Firmware Management . . . . . . . . . . . . . . . . . . . 118
       9.1.1.  Image Data Request  . . . . . . . . . . . . . . . . . 121
       9.1.2.  Image Data Response . . . . . . . . . . . . . . . . . 122
     9.2.  Reset Request . . . . . . . . . . . . . . . . . . . . . . 123
     9.3.  Reset Response  . . . . . . . . . . . . . . . . . . . . . 123
     9.4.  WTP Event Request . . . . . . . . . . . . . . . . . . . . 124
     9.5.  WTP Event Response  . . . . . . . . . . . . . . . . . . . 125
     9.6.  Data Transfer Request . . . . . . . . . . . . . . . . . . 125
     9.7.  Data Transfer Response  . . . . . . . . . . . . . . . . . 126
   10. Station Session Management  . . . . . . . . . . . . . . . . . 127
     10.1. Station Configuration Request . . . . . . . . . . . . . . 127
     10.2. Station Configuration Response  . . . . . . . . . . . . . 127
   11. NAT Considerations  . . . . . . . . . . . . . . . . . . . . . 129
   12. Security Considerations . . . . . . . . . . . . . . . . . . . 131
     12.1. CAPWAP Security . . . . . . . . . . . . . . . . . . . . . 131
       12.1.1. Converting Protected Data into Unprotected Data . . . 132
       12.1.2. Converting Unprotected Data into Protected Data
               (Insertion) . . . . . . . . . . . . . . . . . . . . . 132
       12.1.3. Deletion of Protected Records . . . . . . . . . . . . 132
       12.1.4. Insertion of Unprotected Records  . . . . . . . . . . 132
     12.2. Session ID Security . . . . . . . . . . . . . . . . . . . 132
     12.3. Discovery or DTLS Setup Attacks . . . . . . . . . . . . . 133
     12.4. Interference with a DTLS Session  . . . . . . . . . . . . 134
     12.5. Use of Preshared Keys in CAPWAP . . . . . . . . . . . . . 134
     12.6. Use of Certificates in CAPWAP . . . . . . . . . . . . . . 135
     12.7. AAA Security  . . . . . . . . . . . . . . . . . . . . . . 136
   13. Management Considerations . . . . . . . . . . . . . . . . . . 137
   14. Transport Considerations  . . . . . . . . . . . . . . . . . . 138



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   15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 139
     15.1. CAPWAP Message Types  . . . . . . . . . . . . . . . . . . 139
     15.2. Wireless Binding Identifiers  . . . . . . . . . . . . . . 139
   16. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 140
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . . 141
     17.1. Normative References  . . . . . . . . . . . . . . . . . . 141
     17.2. Informational References  . . . . . . . . . . . . . . . . 142
   Editors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 143
   Intellectual Property and Copyright Statements  . . . . . . . . . 144










































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1.  Introduction

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

   The emergence of centralized IEEE 802.11 Wireless Local Area Network
   (WLAN) architectures, in which simple IEEE 802.11 WTPs are managed by
   an Access Controller (AC) suggested that a standards based,
   interoperable protocol could radically simplify the deployment and
   management of wireless networks.  WTPs require a set of dynamic
   management and control functions related to their primary task of
   connecting the wireless and wired mediums.  Traditional protocols for
   managing WTPs are either manual static configuration via HTTP,
   proprietary Layer 2 specific or non-existent (if the WTPs are self-
   contained).  An IEEE 802.11 binding is defined in [16] to support use
   of the CAPWAP protocol with IEEE 802.11 WLAN networks.

   CAPWAP assumes a network configuration consisting of multiple WTPs
   communicating via the Internet Protocol (IP) to an AC.  WTPs are
   viewed as remote RF interfaces controlled by the AC.  The CAPWAP
   protocol supports two modes of operation: Split and Local MAC.  In
   Split MAC mode all L2 wireless data and management frames are
   encapsulated via the CAPWAP protocol and exchanged between the AC and
   the WTP.  As shown in Figure 1, the wireless frames received from a
   mobile device, which is referred to in this specification as a
   Station (STA), are directly encapsulated by the WTP and forwarded to
   the AC.

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

        Figure 1: Representative CAPWAP Architecture for Split MAC

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



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

        Figure 2: Representative CAPWAP Architecture for Local MAC

   Provisioning WTPs with security credentials, and managing which WTPs
   are authorized to provide service are traditionally handled by
   proprietary solutions.  Allowing these functions to be performed from
   a centralized AC in an interoperable fashion increases manageability
   and allows network operators to more tightly control their wireless
   network infrastructure.

1.1.  Goals

   The goals for the CAPWAP protocol are listed below:

   1. To centralize the authentication and policy enforcement functions
      for a wireless network.  The AC may also provide centralized
      bridging, forwarding, and encryption of user traffic.
      Centralization of these functions will enable reduced cost and
      higher efficiency by applying the capabilities of network
      processing silicon to the wireless network, as in wired LANs.

   2. To enable shifting of the higher level protocol processing from
      the WTP.  This leaves the time critical applications of wireless
      control and access in the WTP, making efficient use of the
      computing power available in WTPs which are the subject to severe
      cost pressure.

   3. To provide a generic encapsulation and transport mechanism,
      enabling the CAPWAP protocol to be applied to many access point
      types in the future, via a specific wireless binding.

   The CAPWAP protocol concerns itself solely with the interface between
   the WTP and the AC.  Inter-AC and station-to AC-communication are
   strictly outside the scope of this document.

1.2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].



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1.3.  Contributing Authors

   This section lists and acknowledges the authors of significant text
   and concepts included in this specification.

   The CAPWAP Working Group selected the Lightweight Access Point
   Protocol (LWAPP) [add reference, when available] to be used as the
   basis of the CAPWAP protocol specification.  The following people are
   authors of the LWAPP document:

      Bob O'Hara, Cisco Systems, Inc.
      170 West Tasman Drive, San Jose, CA  95134
      Phone: +1 408-853-5513, Email: bob.ohara@cisco.com

      Pat Calhoun, Cisco Systems, Inc.
      170 West Tasman Drive, San Jose, CA  95134
      Phone: +1 408-853-5269, Email: pcalhoun@cisco.com

      Rohit Suri, Cisco Systems, Inc.
      170 West Tasman Drive, San Jose, CA  95134
      Phone: +1 408-853-5548, Email: rsuri@cisco.com

      Nancy Cam Winget, Cisco Systems, Inc.
      170 West Tasman Drive, San Jose, CA  95134
      Phone: +1 408-853-0532, Email: ncamwing@cisco.com

      Scott Kelly, Aruba Networks
      1322 Crossman Ave, Sunnyvale, CA 94089
      Phone: +1  408-754-8408, Email: skelly@arubanetworks.com

      Michael Glenn Williams, Nokia, Inc.
      313 Fairchild Drive, Mountain View, CA  94043
      Phone: +1 650-714-7758, Email: Michael.G.Williams@Nokia.com

      Sue Hares, Nexthop Technologies, Inc.
      825 Victors Way, Suite 100, Ann Arbor, MI  48108
      Phone: +1 734 222 1610, Email: shares@nexthop.com

   DTLS is used as the security solution for the CAPWAP protocol.  The
   following people are authors of significant DTLS-related text
   included in this document:

      Scott Kelly, Aruba Networks
      1322 Crossman Ave, Sunnyvale, CA 94089
      Phone: +1  408-754-8408, Email: skelly@arubanetworks.com

      Eric Rescorla, Network Resonance
      2483 El Camino Real, #212,Palo Alto CA, 94303



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      Email: ekr@networkresonance.com

   The concept of using DTLS to secure the CAPWAP protocol was part of
   the Secure Light Access Point Protocol (SLAPP) proposal [add
   reference when available].  The following people are authors of the
   SLAPP proposal:

      Partha Narasimhan, Aruba Networks
      1322 Crossman Ave, Sunnyvale, CA  94089
      Phone: +1 408-480-4716, Email: partha@arubanetworks.com

      Dan Harkins, Tropos Networks
      555 Del Rey Avenue, Sunnyvale, CA, 95085
      Phone: +1 408 470 7372, Email: dharkins@tropos.com

      Subbu Ponnuswamy, Aruba Networks
      1322 Crossman Ave, Sunnyvale, CA  94089
      Phone: +1 408-754-1213, Email: subbu@arubanetworks.com


   The following individuals contributed significant security related
   text to the draft:

      T. Charles Clancy, Laboratory for Telecommunications Sciences,
      8080 Greenmead Drive, College Park, MD 20740
      Phone: +1 240-373-5069, Email: clancy@ltsnet.net

      Scott Kelly, Aruba Networks
      1322 Crossman Ave, Sunnyvale, CA 94089
      Phone: +1  408-754-8408, Email: skelly@arubanetworks.com

1.4.  Terminology

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

   CAPWAP Control Channel: A bi-directional flow defined by the AC IP
   Address, WTP IP Address, AC control port, WTP control port and the
   transport-layer protocol (UDP or UDP-Lite) over which CAPWAP control
   packets are sent and received.

   CAPWAP Data Channel: A bi-directional flow defined by the AC IP
   Address, WTP IP Address, AC data port, WTP data port, and the
   transport-layer protocol (UDP or UDP-Lite) over which CAPWAP data
   packets are sent and received.

   Station (STA): A device that contains an interface to a wireless



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   medium (WM).

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

   This document uses additional terminology defined in [19].












































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2.  Protocol Overview

   The CAPWAP protocol is a generic protocol defining AC and WTP control
   and data plane communication via a CAPWAP protocol transport
   mechanism.  CAPWAP control messages, and optionally CAPWAP data
   messages, are secured using Datagram Transport Layer Security (DTLS)
   [7].  DTLS is a standards-track IETF protocol based upon TLS.  The
   underlying security-related protocol mechanisms of TLS have been
   successfully deployed for many years.

   The CAPWAP protocol Transport layer carries two types of payload,
   CAPWAP Data messages and CAPWAP Control messages.  CAPWAP Data
   messages encapsulate forwarded wireless frames.  CAPWAP protocol
   Control messages are management messages exchanged between a WTP and
   an AC.  The CAPWAP Data and Control packets are sent over separate
   UDP ports.  Since both data and control packets can exceed the
   Maximum Transmission Unit (MTU) length, the payload of a CAPWAP data
   or control message can be fragmented.  The fragmentation behavior is
   defined in Section 3.

   The CAPWAP Protocol begins with a discovery phase.  The WTPs send a
   Discovery Request message, causing any Access Controller (AC)
   receiving the message to respond with a Discovery Response message.
   From the Discovery Response messages received, a WTP selects an AC
   with which to establish a secure DTLS session.  CAPWAP protocol
   messages will be fragmented to the maximum length discovered to be
   supported by the network.

   Once the WTP and the AC have completed DTLS session establishment, a
   configuration exchange occurs in which both devices agree on version
   information.  During this exchange the WTP may receive provisioning
   settings.  The WTP is then enabled for operation.

   When the WTP and AC have completed the version and provision exchange
   and the WTP is enabled, the CAPWAP protocol is used to encapsulate
   the wireless data frames sent between the WTP and AC.  The CAPWAP
   protocol will fragment the L2 frames if the size of the encapsulated
   wireless user data (Data) or protocol control (Management) frames
   causes the resulting CAPWAP protocol packet to exceed the MTU
   supported between the WTP and AC.  Fragmented CAPWAP packets are
   reassembled to reconstitute the original encapsulated payload.  MTU
   Discovery and Fragmentation are described in Section 3.

   The CAPWAP protocol provides for the delivery of commands from the AC
   to the WTP for the management of stations that are communicating with
   the WTP.  This may include the creation of local data structures in
   the WTP for the stations and the collection of statistical
   information about the communication between the WTP and the stations.



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   The CAPWAP protocol provides a mechanism for the AC to obtain
   statistical information collected by the WTP.

   The CAPWAP protocol provides for a keep alive feature that preserves
   the communication channel between the WTP and AC.  If the AC fails to
   appear alive, the WTP will try to discover a new AC.

2.1.  Wireless Binding Definition

   The CAPWAP protocol is independent of a specific WTP radio
   technology.  Elements of the CAPWAP protocol are designed to
   accommodate the specific needs of each wireless technology in a
   standard way.  Implementation of the CAPWAP protocol for a particular
   wireless technology MUST follow the binding requirements defined for
   that technology.

   When defining a binding for wireless technologies, the authors MUST
   include any necessary definitions for technology-specific messages
   and all technology-specific message elements for those messages.  At
   a minimum, a binding MUST provide:

   1. The definition for a binding-specific Statistics message element,
      carried in the WTP Event Request message

   2. A message element carried in the Station Configuration Request
      message to configure station information on the WTP

   3. A WTP Radio Information message element carried in the Discovery,
      Primary Discovery and Join Request and Response messages,
      indicating the binding specific radio types supported at the WTP
      and AC.

   If technology specific message elements are required for any of the
   existing CAPWAP messages defined in this specification, they MUST
   also be defined in the technology binding document.

   The naming of binding-specific message elements MUST begin with the
   name of the technology type, e.g., the binding for IEEE 802.11,
   provided in [16], begins with "IEEE 802.11".

   The CAPWAP binding concept MUST also be used in any future
   specification that add functionality to either the base CAPWAP
   protocol specification, or any published CAPWAP binding
   specification.  A separate WTP Radio Information message element MUST
   be created to properly advertise support for the specification.  This
   mechanism allows for future protocol extensibility, while providing
   the necessary capabilities advertisement, through the WTP Radio
   Information message element, to ensure WTP/AC interoperability.



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2.2.  CAPWAP Session Establishment Overview

   This section describes the session establishment process message
   exchanges in the ideal case.  The annotated ladder diagram shows the
   AC on the right, the WTP on the left, and assumes the use of
   certificates for DTLS authentication.  The CAPWAP Protocol State
   Machine is described in detail in Section 2.3.  Note that DTLS allows
   certain messages to be aggregated into a single frame, which is
   denoted via an asterisk in the following figure.

           ============                         ============
               WTP                                   AC
           ============                         ============
            [----------- begin optional discovery ------------]

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

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

                      (-- begin DTLS handshake --)

                             ClientHello
                 ------------------------------------>
                      HelloVerifyRequest (with cookie)
                 <------------------------------------


                        ClientHello (with cookie)
                 ------------------------------------>
                                ServerHello,
                                Certificate,
                                ServerHelloDone*
                 <------------------------------------

                (-- WTP callout for AC authorization --)

                        Certificate (optional),
                         ClientKeyExchange,
                     CertificateVerify (optional),
                         ChangeCipherSpec,
                             Finished*
                 ------------------------------------>

                (-- AC callout for WTP authorization --)




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                         ChangeCipherSpec,
                             Finished*
                 <------------------------------------

                (-- DTLS session is established now --)

                              Join Request
                 ------------------------------------>
                              Join Response
                 <------------------------------------
                      [-- Join State Complete --]

                   (-- assume image is up to date --)

                      Configuration Status Request
                 ------------------------------------>
                      Configuration Status Response
                 <------------------------------------
                    [-- Configure State Complete --]

                       Change State Event Request
                 ------------------------------------>
                       Change State Event Response
                 <------------------------------------
                   [-- Data Check State Complete --]

                        (-- enter RUN state --)

                                   :
                                   :

                              Echo Request
                 ------------------------------------>
                             Echo Response
                 <------------------------------------

                                   :
                                   :

                              Event Request
                 ------------------------------------>
                             Event Response
                 <------------------------------------

                                   :
                                   :

   At the end of the illustrated CAPWAP message exchange, the AC and WTP



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   are securely exchanging CAPWAP control messages.  This is an
   idealized illustration, provided to clarify protocol operation.
   Section 2.3 provides a detailed description of the corresponding
   state machine.

2.3.  CAPWAP State Machine Definition

   The following state diagram represents the lifecycle of a WTP-AC
   session.  Use of DTLS by the CAPWAP protocol results in the
   juxtaposition of two nominally separate yet tightly bound state
   machines.  The DTLS and CAPWAP state machines are coupled through an
   API consisting of commands (see Section 2.3.2.1) and notifications
   (see Section 2.3.2.2).  Certain transitions in the DTLS state machine
   are triggered by commands from the CAPWAP state machine, while
   certain transitions in the CAPWAP state machine are triggered by
   notifications from the DTLS state machine.



































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                            /-------------------------------------\
                            |          /-------------------------\|
                            |         w|                         ||
                            |    x+----------+ y +------------+  ||
                            |     |   Run    |-->|   Reset    |-\||
                            |     +----------+   +------------+ |||
                           u|  V      ^           ^     ^      z|||
                +------------+--------/           |     |       |||
                | Data Check |             /-------/    |       |||
                +------------+<-------\   |             |       |||
                                      |   |             |       |||
                       /------------------+--------\    |       |||
                      m|             t|  o|    q   v   r|       |||
               +--------+     +-----------+     +--------------+|||
               |  Join  |---->| Configure |     |  Image Data  ||||
               +--------+  n  +-----------+     +--------------+|||
                ^   |l                 p|                    s| |||
                |   |                   \-------------------\ | |||
                |   \--------------------------------------\| | |||
                \------------------------\                 || | |||
         /--------------<----------------+---------------\ || | |||
         | /------------<----------------+-------------\ | || | |||
         | |                       i      |k           8| | vv v vvv
         | |   +----------------+<--+--------------+   +-----------+
     /---|-|---|   DTLS Setup   |   | DTLS Connect |-->|  DTLS TD  |
     | /-|-|---+----------------+e  +--------------+ 7 +-----------+
     | | | | d  |6  ^      ^  |f         ^       j|      ^  |~
     v v v v    |   |      |  |          |        |      |  |
     | | | |    |   |      |  \-------\  |   /----+------/  |
     | | | |    |   |      |          |  |   |    \---\     |
     | | | |    v  c|  1   |5    2    v  |g  |h       v     v
     | | | \->+------+-->+------+   +-----------+    +--------+
     | | |    | Idle |   | Disc |   | Authorize |    |  Dead  |
     | | |    +------+<--+------+   +-----------+    +--------+
     | | |        ^    0      |3                         ^
     | | |        |           |                          |b
     | | |9       |4          |                          |
     | | \->+---------+<------/                          |
     | \--->| Sulking |                                  |
     |      +---------+a                                 |
     \---------------------------------------------------/

                 Figure 3: CAPWAP Integrated State Machine

   The CAPWAP protocol state machine, depicted above, is used by both
   the AC and the WTP.  In cases where states are not shared (i.e. not
   implemented in one or the other of the AC or WTP), this is explicitly
   called out in the transition descriptions below.  For every state



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   defined, only certain messages are permitted to be sent and received.
   The CAPWAP control message definitions specify the state(s) in which
   each message is valid.

   Since the WTP only communicates with a single AC, it only has a
   single instance of the CAPWAP state machine.  The state machine works
   differently on the AC since it communicates with many WTPs.  The AC
   uses the concept of two threads.  Note that the term thread used here
   does not necessarily imply that implementers must use threads, but it
   is one possible way of implementing the AC's state machine.

   Listener Thread -   The AC's Listener thread handles the shared
      services, which includes receiving and responding to Discovery
      Request messages.  The Listener thread handles the common tasks,
      up to the DTLS Setup state.  The state machine transitions in
      figure Figure 3are represented by numerals.  It is necessary for
      the AC to protect itself against various attacks that exist with
      non-authenticated frames.  See Section 12 for more information.

   Service Thread -   The AC's Service thread handles the per-WTP
      states, and one such thread exists per-WTP connection.  This
      thread starts during the DTLS Setup state, which is when the
      DTLSListen command is invoked.  When created, the Service thread
      inherits a copy of the state machine context from the Listener
      thread.  When communication with the WTP is complete, the Service
      thread is terminated.  The state machine transitions in the above
      figure are represented by alphabetic characters (including
      symbols).

2.3.1.  CAPWAP Protocol State Transitions

   This section describes the various state transitions, and the events
   that cause them.  This section does not discuss interactions between
   DTLS- and CAPWAP-specific states.  Those interactions, and DTLS-
   specific states and transitions, are discussed in Section 2.3.2.

   Idle to Discovery (1):  This transition occurs once device
      initialization is complete.

      WTP:  The WTP enters the Discovery state prior to transmitting the
         first Discovery Request message (see Section 5.1).  Upon
         entering this state, the WTP sets the DiscoveryInterval timer
         (see Section 4.7).  The WTP resets the DiscoveryCount counter
         to zero (0) (see Section 4.8).  The WTP also clears all
         information from ACs it may have received during a previous
         Discovery phase.





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      AC:  This state transition is executed by the AC's Listener
         thread, and occurs when a Discovery Request message is
         received.  The AC SHOULD respond with a Discovery Response
         message (see Section 5.2).  The AC SHOULD NOT maintain WTP
         state at this point (see Section 12 for more information).

   Discovery to Discovery (2):  In the Discovery state, the WTP
      determines which AC to connect to.

      WTP:  This transition occurs when the DiscoveryInterval timer
         expires.  If the WTP is configured with a list of ACs, it
         transmits a Discovery Request message to every AC from which it
         has not received a Discovery Response message.  For every
         transition to this event, the WTP increments the DiscoveryCount
         counter.  See Section 5.1 for more information on how the WTP
         knows the ACs to which it should transmit the Discovery Request
         messages.  The WTP restarts the DiscoveryInterval timer
         whenever it transmits Discovery Request messages.

      AC:  This is an invalid state transition for the AC.

   Discovery to Idle (0):  This transition occurs on the AC's Listener
      thread when the Discovery processing is complete.

      WTP:  This is an invalid state transition for the WTP.

      AC:  This state transition is executed by the AC's Listener thread
         when it has transmitted the Discovery Response, in response to
         a Discovery Request.

   Discovery to Sulking (3):  This transition occurs on a WTP when AC
      Discovery fails.

      WTP:  The WTP enters this state when the DiscoveryInterval timer
         expires and the DiscoveryCount variable is equal to the
         MaxDiscoveries variable (see Section 4.8).  Upon entering this
         state, the WTP MUST start the SilentInterval timer.  While in
         the Sulking state, all received CAPWAP protocol messages MUST
         be ignored.

      AC:  This is an invalid state transition for the AC.

   Sulking to Idle (4):  This transition occurs on a WTP when it must
      restart the discovery phase.







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      WTP:  The WTP enters this state when the SilentInterval timer (see
         Section 4.7) expires.  The FailedDTLSSessionCount,
         DiscoveryCount and FailedDTLSAuthFailCount counters are reset
         to zero.

      AC:  This is an invalid state transition for the AC.

   Sulking to Sulking (a):  The Sulking state provides the silent
      period, minimizing the possibility for Denial of Service (DoS)
      attacks.

      WTP:  All packets received from the AC while in the sulking state
         are ignored.

      AC:  This is an invalid state transition for the AC.

   Idle to DTLS Setup (c):  This transition occurs to establish a secure
      DTLS session with the peer.

      WTP:  The WTP initiates this transition by invoking the DTLSStart
         command, which starts the DTLS session establishment with the
         chosen AC.  When the discovery phase is bypassed, it is assumed
         the WTP has locally configured ACs.

      AC:  The AC initiates this transition by invoking the DTLSListen
         command (see Section 2.3.2.1), which informs the DTLS stack
         that it is willing to listen for an incoming session.  The AC's
         Listener thread forks an instance of the Service thread, along
         with a copy of the state context.  If the AC had maintained WTP
         state information during the Discovery exchange, or through
         some other means that may include static configuration of WTPs,
         the AC MAY provide optional qualifiers in the DTLSListen
         command to only accept session requests a specific WTP.  Note
         that the AC SHOULD NOT maintain state information based on an
         unsecured Discovery Request message, as this can lead to a
         Denial of Service attack (see Section 12).  However, in the
         event that the AC does maintain state, it MUST ensure that the
         state information is freed after a period, which is
         implementation specific.

   Discovery to DTLS Setup (5):  This transition occurs to establish a
      secure DTLS session with the peer.

      WTP:  The WTP initiates this transition by invoking the DTLSStart
         command (see Section 2.3.2.1), which starts the DTLS session
         establishment with the chosen AC.  The decision of which AC to
         connect to is the result of the discovery phase, which is
         described in Section 3.3.



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      AC:  This is an invalid state transition for the AC.

   DTLS Setup to Idle (6):  This transition occurs when the DTLS
      connection setup fails.

      WTP:  The WTP initiates this state transition when it receives a
         DTLSEstablishFail notification from DTLS (see Section 2.3.2.2),
         and the FailedDTLSSessionCount or the FailedDTLSAuthFailCount
         counter have not reached the value of the
         MaxFailedDTLSSessionRetry variable (see Section 4.8).  This
         error notification aborts the secure DTLS session
         establishment.  When this notification is received, the
         FailedDTLSSessionCount counter is incremented.

      AC:  This is an invalid state transition for the AC.

   DTLS Setup to Sulking (d):  This transition occurs when repeated
      attempts to setup the DTLS connection have failed.

      WTP:  The WTP enters this state when the FailedDTLSSessionCount or
         the FailedDTLSAuthFailCount counter reaches the value of the
         MaxFailedDTLSSessionRetry variable (see Section 4.8).  Upon
         entering this state, the WTP MUST start the SilentInterval
         timer.  While in the Sulking state, all received CAPWAP and
         DTLS protocol messages received MUST be ignored.

      AC:  This is an invalid state transition for the AC.

   DTLS Setup to Dead (b):  This transition occurs on the AC when the
      DTLS connection setup fails.

      WTP:  This is an invalid state transition for the WTP.

      AC:  The AC initiates this state transition when it receives a
         DTLSEstablishFail notification from DTLS (see Section 2.3.2.2).
         This error notification aborts the secure DTLS session
         establishment.  When this notification is received, the
         FailedDTLSSessionCount counter is incremented.  The AC must
         release all resources associated with the control plane DTLS
         session.  The data plane DTLS session is also shutdown, and all
         resources released, if a DTLS session was established for the
         data plane.  Any timers set for the current instance of the
         state machine are also cleared.  The AC's Service thread is
         terminated.







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   DTLS Setup to DTLS Setup (e):  This transition occurs when the DTLS
      Session failed to be established.

      WTP:  This is an invalid state transition for the WTP.

      AC:  The AC initiates this state transition by the Service thread
         when it receives a DTLSEstablishFail notification from DTLS
         (see Section 2.3.2.2).  This error notification aborts the
         secure DTLS session establishment.  When this notification is
         received, the FailedDTLSSessionCount counter is incremented.

   DTLS Setup to Authorize (f):  This transition occurs when an incoming
      DTLS session is being established, and the DTLS stack needs
      authorization to proceed with the session establishment.

      WTP:  This state transition occurs when the WTP receives the
         DTLSPeerAuthorize notification (see Section 2.3.2.2).  Upon
         entering this state, the WTP performs an authorization check
         against the AC credentials.  See Section 2.4.4 for more
         information on AC authorization.

      AC:  This state transition occurs when the AC receives the
         DTLSPeerAuthorize notification (see Section 2.3.2.2).  Upon
         entering this state, the AC performs an authorization check
         against the WTP credentials.  See Section 2.4.4 for more
         information on WTP authorization.

   Authorize to DTLS Connect (g):  This transition occurs to notify the
      DTLS stack that the session should be established.

      WTP:  This state transition occurs when the WTP has successfully
         authorized the AC's credentials (see Section 2.4.4).  This is
         done by invoking the DTLSAccept DTLS command (see
         Section 2.3.2.1).

      AC:  This state transition occurs when the AC has successfully
         authorized the WTP's credentials (see Section 2.4.4).  This is
         done by invoking the DTLSAccept DTLS command (see
         Section 2.3.2.1).

   Authorize to DTLS Teardown (h):  This transition occurs to notify the
      DTLS stack that the session should be aborted.

      WTP:  This state transition occurs when the WTP was unable to
         authorize the AC, using the AC credentials.  The WTP then
         aborts the DTLS session by invoking the DTLSAbortSession
         command (see Section 2.3.2.1).




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      AC:  This state transition occurs when the AC was unable to
         authorize the WTP, using the WTP credentials.  The AC then
         aborts the DTLS session by invoking the DTLSAbortSession
         command (see Section 2.3.2.1).

   DTLS Connect to DTLS Teardown (7):  This transition occurs when the
      DTLS Session failed to be established.

      WTP:  This state transition occurs when the WTP receives either a
         DTLSAborted or DTLSAuthenticateFail notification (see
         Section 2.3.2.2), indicating that the DTLS session was not
         successfully established.  When this transition occurs due to
         the DTLSAuthenticateFail notification, the
         FailedDTLSAuthFailCount is incremented, otherwise the
         FailedDTLSSessionCount counter is incremented.

      AC:  This is an invalid state transition for the AC.

   DTLS Connect to DTLS Setup (i):  This transition occurs when the DTLS
      Session failed to be established.

      WTP:  This is an invalid state transition for the WTP.

      AC:  This state transition occurs when the AC receives either a
         DTLSAborted or DTLSAuthenticateFail notification (see
         Section 2.3.2.2), indicating that the DTLS session was not
         successfully established, and both of the
         FailedDTLSAuthFailCount and FailedDTLSSessionCount counters
         have not reached the value of the MaxFailedDTLSSessionRetry
         variable (see Section 4.8).

   DTLS Connect to Dead (j):  This transition occurs when the DTLS
      Session failed to be established.

      WTP:  This is an invalid state transition for the WTP.

      AC:  This state transition occurs when the AC receives either a
         DTLSAborted or DTLSAuthenticateFail notification (see
         Section 2.3.2.2), indicating that the DTLS session was not
         successfully established, and either the
         FailedDTLSAuthFailCount and FailedDTLSSessionCount counters
         have reached the value of the MaxFailedDTLSSessionRetry
         variable (see Section 4.8).








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   DTLS Connect to Join (k):  This transition occurs when the DTLS
      Session is successfully established.

      WTP:  This state transition occurs when the WTP receives the
         DTLSEstablished notification (see Section 2.3.2.2), indicating
         that the DTLS session was successfully established.  When this
         notification is received, the FailedDTLSSessionCount counter is
         set to zero.

      AC:  This state transition occurs when the AC receives the
         DTLSEstablished notification (see Section 2.3.2.2), indicating
         that the DTLS session was successfully established.  When this
         notification is received, the FailedDTLSSessionCount counter is
         set to zero, and the WaitJoin timer is started (see
         Section 4.7).

   Join to DTLS Teardown (l):  This transition occurs when the join
      process failed.

      WTP:  This state transition occurs when the WTP receives a Join
         Response message with a Result Code message element containing
         an error, if the Image Identifier provided by the AC in the
         Join Response message differs from the WTP's currently running
         firmware version and the WTP has the requested image in its
         non-volatile memory, or if the WaitDTLS timer expires.  This
         causes the WTP to initiate the DTLSShutdown command (see
         Section 2.3.2.1).  This transition also occurs if the WTP
         receives one of the following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect.

      AC:  This state transition occurs either if the WaitJoin timer
         expires or if the AC transmits a Join Response message with a
         Result Code message element containing an error.  This causes
         the AC to initiate the DTLSShutdown command (see
         Section 2.3.2.1).  This transition also occurs if the AC
         receives one of the following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect.

   Join to Image Data (m):  This state transition is used by the WTP and
      the AC to download executable firmware.

      WTP:  The WTP enters the Image Data state when it receives a
         successful Join Response message and determines and the
         included Image Identifier message element is not the same as
         its currently running image.  The WTP also detects that the
         requested image version is not currently available in the WTP's
         non-volatile storage (see Section 9.1 for a full description of
         the firmware download process).  The WTP initializes the



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         EchoInterval timer (see Section 4.7), and transmits the Image
         Data Request message (see Section 9.1.1) requesting the start
         of the firmware download.

      AC:  This state transition occurs when the AC receives the Image
         Data Request message from the WTP.  The AC MUST transmit an
         Image Data Response message (see Section 9.1.2) to the WTP,
         which includes a portion of the firmware.  The AC MUST start
         the ImageDataStartTimer timer (see Section 4.7).

   Join to Configure (n):  This state transition is used by the WTP and
      the AC to exchange configuration information.

      WTP:  The WTP enters the Configure state when it receives a
         successful Join Response message, and determines that the
         included Image Identifier message element is the same as its
         currently running image.  The WTP transmits the Configuration
         Status message (see Section 8.2) to the AC with message
         elements describing its current configuration.  The WTP also
         starts the ResponseTimeout timer (see Section 4.7).

      AC:  This state transition occurs immediately after the AC
         transmits the Join Response message to the WTP.  If the AC
         receives the Configuration Status message from the WTP, the AC
         MUST transmit a Configuration Status Response message (see
         Section 8.3) to the WTP, and MAY include specific message
         elements to override the WTP's configuration.  The AC also
         starts the ChangeStatePendingTimer timer (see Section 4.7).

   Configure to Reset (o):  This state transition is used to reset the
      connection either due to an error during the configuration phase,
      or when the WTP determines it needs to reset in order for the new
      configuration to take effect.

      WTP:  The WTP enters the Reset state when it receives a
         Configuration Status Response message indicating an error or
         when it determines that a reset of the WTP is required, due to
         the characteristics of a new configuration.

      AC:  The AC transitions to the Reset state when it receives a
         Change State Event message from the WTP that contains an error
         for which AC policy does not permit the WTP to provide service.
         This state transition also occurs when the AC
         ChangeStatePendingTimer timer expires.







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   Configure to DTLS Teardown (p):  This transition occurs when the
      configuration process aborts due to a DTLS error.

      WTP:  The WTP enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.

      AC:  The AC enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.

   Image Data to Image Data (q):  The Image Data state is used by the
      WTP and the AC during the firmware download phase.

      WTP:  The WTP enters the Image Data state when it receives an
         Image Data Response message indicating that the AC has more
         data to send.

      AC:  This state transition occurs when the AC receives the Image
         Data Request message from the WTP while already in the Image
         Data state.  The AC resets the ImageDataStartTimer timer.

   Image Data to Reset (r):  This state transition is used to reset the
      DTLS connection prior to restarting the WTP after an image
      download.

      WTP:  When an image download completes, the WTP enters the Reset
         state.  The WTP MAY also transition to this state upon
         receiving an Image Data Response message from the AC (see
         Section 9.1.2) indicating a failure.

      AC:  The AC enters the Reset state when an error occurs during the
         image download process or if the ImageDataStartTimer timer
         expires.

   Image Data to DTLS Teardown (s):  This transition occurs when the
      firmware download process aborts due to a DTLS error.

      WTP:  The WTP enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.




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      AC:  The AC enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.

   Configure to Data Check (t):  This state transition occurs when the
      WTP and AC confirm the configuration.

      WTP:  The WTP enters this state when it receives a successful
         Configuration Status Response message from the AC.  The WTP
         initializes the EchoInterval timer (see Section 4.7), and
         transmits the Change State Event Request message (see
         Section 8.6).

      AC:  This state transition occurs when the AC receives the Change
         State Event Request message (see Section 8.6) from the WTP.
         The AC responds with a Change State Event Response message (see
         Section 8.7).  The AC MUST start the DataCheckTimer timer (see
         Section 4.7).

   Data Check to DTLS Teardown (u):  This transition occurs when the WTP
      does not complete the Data Check exchange.

      WTP:  This state transition occurs if the WTP does not receive the
         Change State Event Response message before a CAPWAP
         transmission timeout occurs.

      AC:  The AC enters this state when the DataCheckTimer timer
         expires (see Section 4.7).

   Data Check to Run (V):  This state transition occurs when the linkage
      between the control and data channels is established, causing the
      WTP and AC to enter their normal state of operation.

      WTP:  The WTP enters this state when it receives a successful
         Change State Event Response message from the AC.  The WTP
         initiates the data channel, which MAY require the establishment
         of a DTLS session, starts the DataChannelKeepAlive timer (see
         Section 4.7) and transmits a Data Channel Keep Alive packet
         (see Section 4.4.1).  The WTP then starts the
         DataChannelDeadInterval timer (see Section 4.7).

      AC:  This state transition occurs when the AC receives the Data
         Channel Keep Alive packet (see Section 4.4.1), with a Session
         ID message element matching that included by the WTP in the
         Join Request message.  The AC disables the DataCheckTimer
         timer.  Note that if AC policy is to require the data channel



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         to be encrypted, this process would also require the
         establishment of a data channel DTLS session.  Upon receiving
         the Data Channel Keep Alive packet, the AC transmits its own
         Data Channel Keep Alive packet.

   Run to DTLS Teardown (w):  This state transition occurs when an error
      has occurred in the DTLS stack, causing the DTLS session to be
      torn down.

      WTP:  The WTP enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.  The WTP also
         transitions to this state if the underlying reliable
         transport's RetransmitCount counter has reached the
         MaxRetransmit variable (see Section 4.7).

      AC:  The AC enters this state when it receives one of the
         following DTLS notifications: DTLSAborted,
         DTLSReassemblyFailure or DTLSPeerDisconnect (see
         Section 2.3.2.2).  The WTP MAY tear down the DTLS session if it
         receives frequent DTLSDecapFailure notifications.  The AC
         transitions to this state if the underlying reliable
         transport's RetransmitCount counter has reached the
         MaxRetransmit variable (see Section 4.7).

   Run to Run (x):  This is the normal state of operation.

      WTP:  This is the WTP's normal state of operation.  There are many
         events that result this state transition:

         Configuration Update:  The WTP receives a Configuration Update
            Request message(see Section 8.4).  The WTP MUST respond with
            a Configuration Update Response message (see Section 8.5).

         Change State Event:  The WTP receives a Change State Event
            Response message, or determines that it must initiate a
            Change State Event Request message, as a result of a failure
            or change in the state of a radio.

         Echo Request:  The WTP sends an Echo Request message
            (Section 7.1) or receives the corresponding Echo Response
            message, (see Section 7.2) from the AC.







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         Clear Config Request:  The WTP receives a Clear Configuration
            Request message (see Section 8.8).  The WTP MUST reset its
            configuration back to manufacturer defaults.

         WTP Event:  The WTP sends a WTP Event Request message,
            delivering information to the AC (see Section 9.4).  The WTP
            receives a WTP Event Response message from the AC (see
            Section 9.5).

         Data Transfer:  The WTP sends a Data Transfer Request message
            to the AC (see Section 9.6).  The WTP receives a Data
            Transfer Response message from the AC (see Section 9.7).

         Station Configuration Request:  The WTP receives a Station
            Configuration Request message (see Section 10.1), to which
            it MUST respond with a Station Configuration Response
            message (see Section 10.2).

      AC:  This is the AC's normal state of operation:

         Configuration Update:  The AC sends a Configuration Update
            Request message (see Section 8.4) to the WTP to update its
            configuration.  The AC receives a Configuration Update
            Response message (see Section 8.5) from the WTP.

         Change State Event:  The AC receives a Change State Event
            Request message (see Section 8.6), to which it MUST respond
            with the Change State Event Response message (see
            Section 8.7).

         Echo Request:  The AC receives an Echo Request message (see
            Section 7.1), to which it MUST respond with an Echo Response
            message(see Section 7.2).

         Clear Config Response:  The AC receives a Clear Configuration
            Response message from the WTP (see Section 8.9).

         WTP Event:  The AC receives a WTP Event Request message from
            the WTP (see Section 9.4) and MUST generate a corresponding
            WTP Event Response message (see Section 9.5).

         Data Transfer:  The AC receives a Data Transfer Request message
            from the WTP (see Section 9.6) and MUST generate a
            corresponding Data Transfer Response message (see
            Section 9.7).






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         Station Configuration Request:  The AC sends a Station
            Configuration Request message (see Section 10.1) or receives
            the corresponding Station Configuration Response message
            (see Section 10.2) from the WTP.

   Run to Reset (y):  This state transition is used when either the AC
      or WTP tear down the connection.  This may occur as part of normal
      operation, or due to error conditions.

      WTP:  The WTP enters the Reset state when it receives a Reset
         Request message from the AC.

      AC:  The AC enters the Reset state when it transmits a Reset
         Request message to the WTP.

   Reset to DTLS Teardown (z):  This transition occurs when the CAPWAP
      reset is complete, to terminate the DTLS session.

      WTP:  This state transition occurs when the WTP receives a Reset
         Response message.  This causes the WTP to initiate the
         DTLSShutdown command (see Section 2.3.2.1).

      AC:  This state transition occurs when the AC transmits a Reset
         Response message.  The AC does not invoke the DTLSShutdown
         command (see Section 2.3.2.1).

   DTLS Teardown to Idle (8):  This transition occurs when the DTLS
      session has been shutdown.

      WTP:  This state transition occurs when the WTP has successfully
         cleaned up all resources associated with the control plane DTLS
         session.  The data plane DTLS session is also shutdown, and all
         resources released, if a DTLS session was established for the
         data plane.  Any timers set for the current instance of the
         state machine are also cleared.

      AC:  This is an invalid state transition for the AC.

   DTLS Teardown to Sulking (9):  This transition occurs when repeated
      attempts to setup the DTLS connection have failed.

      WTP:  The WTP enters this state when the FailedDTLSSessionCount or
         the FailedDTLSAuthFailCount counter reaches the value of the
         MaxFailedDTLSSessionRetry variable (see Section 4.8).  Upon
         entering this state, the WTP MUST start the SilentInterval
         timer.  While in the Sulking state, all received CAPWAP and
         DTLS protocol messages received MUST be ignored.




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      AC:  This is an invalid state transition for the AC.

   DTLS Teardown to Dead (~):  This transition occurs when the DTLS
      session has been shutdown.

      WTP:  This is an invalid state transition for the WTP.

      AC:  This state transition occurs when the AC has successfully
         cleaned up all resources associated with the control plane DTLS
         session.  The data plane DTLS session is also shutdown, and all
         resources released, if a DTLS session was established for the
         data plane.  Any timers set for the current instance of the
         state machine are also cleared.  The AC's Service thread is
         terminated.

2.3.2.  CAPWAP/DTLS Interface

   This section describes the DTLS Commands used by CAPWAP, and the
   notifications received from DTLS to the CAPWAP protocol stack.

2.3.2.1.  CAPWAP to DTLS Commands

   Six commands are defined for the CAPWAP to DTLS API.  These
   "commands" are conceptual, and may be implemented as one or more
   function calls.  This API definition is provided to clarify
   interactions between the DTLS and CAPWAP components of the integrated
   CAPWAP state machine.

   Below is a list of the minimal command API:

   o  DTLSStart is sent to the DTLS component to cause a DTLS session to
      be established.  Upon invoking the DTLSStart command, the WaitDTLS
      timer is started.  The WTP initiates this DTLS command, as the AC
      does not initiate DTLS sessions.

   o  DTLSListen is sent to the DTLS component to allow the DTLS
      component to listen for incoming DTLS session requests.

   o  DTLSAccept is sent to the DTLS component to allow the DTLS session
      establishment to continue successfully.

   o  DTLSAbortSession is sent to the DTLS component to cause the
      session that is in the process of being established to be aborted.
      This command is also sent when the WaitDTLS timer expires.  When
      this command is executed, the FailedDTLSSessionCount counter is
      incremented.





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   o  DTLSShutdown is sent to the DTLS component to cause session
      teardown.

   o  DTLSMtuUpdate is sent by the CAPWAP component to modify the MTU
      size used by the DTLS component.  See Section 3.5 for more
      information on MTU Discovery.  The default size is 1468 bytes.

2.3.2.2.  DTLS to CAPWAP Notifications

   DTLS notifications are defined for the DTLS to CAPWAP API.  These
   "notifications" are conceptual, and may be implemented in numerous
   ways (e.g. as function return values).  This API definition is
   provided to clarify interactions between the DTLS and CAPWAP
   components of the integrated CAPWAP state machine.  It is important
   to note that the notifications listed below MAY cause the CAPWAP
   state machine to jump from one state to another using a state
   transition not listed in Section 2.3.1.  When a notification listed
   below occurs, the target CAPWAP state shown in Figure 3 becomes the
   current state.

   Below is a list of the API notifications:

   o  DTLSPeerAuthorize is sent to the CAPWAP component during DTLS
      session establishment once the peer's identity has been received.
      This notification MAY be used by the CAPWAP component to authorize
      the session, based on the peer's identity.  The authorization
      process will lead to the CAPWAP component initiating either the
      DTLSAccept or DTLSAbortSession commands.

   o  DTLSEstablished is sent to the CAPWAP component to indicate that
      that a secure channel now exists, using the parameters provided
      during the DTLS initialization process.  When this notification is
      received, the FailedDTLSSessionCount counter is reset to zero.
      When this notification is received, the WaitDTLS timer is stopped.

   o  DTLSEstablishFail is sent when the DTLS session establishment has
      failed, either due to a local error, or due to the peer rejecting
      the session establishment.  When this notification is received,
      the FailedDTLSSessionCount counter is incremented.

   o  DTLSAuthenticateFail is sent when DTLS session establishment
      failed due to an authentication error.  When this notification is
      received, the FailedDTLSAuthFailCount counter is incremented.

   o  DTLSAborted is sent to the CAPWAP component to indicate that
      session abort (as requested by CAPWAP) is complete; this occurs to
      confirm a DTLS session abort, or when the WaitDTLS timer expires.
      When this notification is received, the WaitDTLS timer is stopped.



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   o  DTLSReassemblyFailure MAY be sent to the CAPWAP component to
      indicate DTLS fragment reassembly failure.

   o  DTLSDecapFailure MAY be sent to the CAPWAP module to indicate a
      decapsulation failure.  DTLSDecapFailure MAY be sent to the CAPWAP
      module to indicate an encryption/authentication failure.  This
      notification is intended for informative purposes only, and is not
      intended to cause a change in the CAPWAP state machine (see
      Section 12.4).

   o  DTLSPeerDisconnect is sent to the CAPWAP component to indicate the
      DTLS session has been torn down.  Note that this notification is
      only received if the DTLS session has been established.

2.4.  Use of DTLS in the CAPWAP Protocol

   DTLS is used as a tightly-integrated, secure wrapper for the CAPWAP
   protocol.  In this document DTLS and CAPWAP are discussed as
   nominally distinct entities; however they are very closely coupled,
   and may even be implemented inseparably.  Since there are DTLS
   library implementations currently available, and since security
   protocols (e.g.  IPsec, TLS) are often implemented in widely
   available acceleration hardware, it is both convenient and forward-
   looking to maintain a modular distinction in this document.

   This section describes a detailed walk-through of the interactions
   between the DTLS module and the CAPWAP module, via 'commands' (CAPWAP
   to DTLS) and 'notifications' (DTLS to CAPWAP) as they would be
   encountered during the normal course of operation.

2.4.1.  DTLS Handshake Processing

   Details of the DTLS handshake process are specified in [8].  This
   section describes the interactions between the DTLS session
   establishment process and the CAPWAP protocol.  Note that the
   conceptual DTLS state is shown below to help understand the point at
   which the DTLS states transition.  In the normal case, the DTLS
   handshake will proceed as follows (NOTE: this example uses
   certificates, but preshared keys are also supported):












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           ============                         ============
               WTP                                   AC
           ============                         ============
           ClientHello           ------>
                                 <------       HelloVerifyRequest
                                                   (with cookie)

           ClientHello           ------>
           (with cookie)
                                 <------       ServerHello
                                 <------       Certificate
                                 <------       ServerHelloDone

           (WTP callout for AC authorization
                    occurs in CAPWAP Auth state)

           Certificate*
           ClientKeyExchange
           CertificateVerify*
           [ChangeCipherSpec]
           Finished              ------>

                                (AC callout for WTP authorization
                                 occurs in CAPWAP Auth state)

                                               [ChangeCipherSpec]
                                 <------       Finished


   DTLS, as specified, provides its own retransmit timers with an
   exponential back-off.  However, DTLS will never terminate the
   handshake due to non-responsiveness; instead, DTLS will continue to
   increase its back-off timer period.  Hence, timing out incomplete
   DTLS handshakes is entirely the responsibility of the CAPWAP module.

   The DTLS implementation used by CAPWAP MUST support TLS Session
   Resumption.  Session resumption is used to establish the DTLS session
   used for the data channel.  The DTLS implementation on the WTP MUST
   return some unique identifier to the CAPWAP module to enable
   subsequent establishment of a DTLS-encrypted data channel, if
   necessary.

2.4.2.  DTLS Session Establishment

   The WTP, either through the Discovery process, or through pre-
   configuration, determines the AC to connect to.  The WTP uses the
   DTLSStart command to request that a secure connection be established
   to the selected AC.  Prior to initiation of the DTLS handshake, the



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   WTP sets the WaitDTLS timer.  Upon receiving the DTLSPeerAuthorize
   DTLS notification, the AC sets the WaitDTLS timer.  If the
   DTLSEstablished notification is not received prior to timer
   expiration, the DTLS session is aborted by issuing the
   DTLSAbortSession DTLS command.  This notification causes the CAPWAP
   module to transition to the Idle state.  Upon receiving a
   DTLSEstablished notification, the WaitDTLS timer is deactivated.

2.4.3.  DTLS Error Handling

   If the AC does not respond to any DTLS messages sent by the WTP, the
   DTLS specification calls for the WTP to retransmit these messages.
   If the WaitDTLS timer expires, CAPWAP will issue the DTLSAbortSession
   command, causing DTLS to terminate the handshake and remove any
   allocated session context.  Note that DTLS MAY send a single TLS
   Alert message to the AC to indicate session termination.

   If the WTP does not respond to any DTLS messages sent by the AC, the
   CAPWAP protocol allows for three possibilities, listed below.  Note
   that DTLS MAY send a single TLS Alert message to the AC to indicate
   session termination.

   o  The message was lost in transit; in this case, the WTP will re-
      transmit its last outstanding message, since it did not receive a
      reply.

   o  The WTP sent a DTLS Alert, which was lost in transit; in this
      case, the AC's WaitDTLS timer will expire, and the session will be
      terminated.

   o  Communication with the WTP has completely failed; in this case,
      the AC's WaitDTLS timer will expire, and the session will be
      terminated.

   The DTLS specification provides for retransmission of unacknowledged
   requests.  If retransmissions remain unacknowledged, the WaitDTLS
   timer will eventually expire, at which time the CAPWAP component will
   terminate the session.

   If a cookie fails to validate, this could represent a WTP error, or
   it could represent a DoS attack.  Hence, AC resource utilization
   SHOULD be minimized.  The AC MAY log a message indicating the
   failure, but SHOULD NOT attempt to reply to the WTP.

   Since DTLS handshake messages are potentially larger than the maximum
   record size, DTLS supports fragmenting of handshake messages across
   multiple records.  There are several potential causes of re-assembly
   errors, including overlapping and/or lost fragments.  The DTLS



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   component MUST send a DTLSReassemblyFailure notification to the
   CAPWAP component.  Whether precise information is given along with
   notification is an implementation issue, and hence is beyond the
   scope of this document.  Upon receipt of such an error, the CAPWAP
   component SHOULD log an appropriate error message.  Whether
   processing continues or the DTLS session is terminated is
   implementation dependent.

   DTLS decapsulation errors consist of three types: decryption errors,
   authentication errors, and malformed DTLS record headers.  Since DTLS
   authenticates the data prior to encapsulation, if decryption fails,
   it is difficult to detect this without first attempting to
   authenticate the packet.  If authentication fails, a decryption error
   is also likely, but not guaranteed.  Rather than attempt to derive
   (and require the implementation of) algorithms for detecting
   decryption failures, decryption failures are reported as
   authentication failures.  The DTLS component MUST provide a
   DTLSDecapFailure notification to the CAPWAP component when such
   errors occur.  If a malformed DTLS record header is detected, the
   packets SHOULD be silently discarded, and the receiver MAY log an
   error message.

   There is currently only one encapsulation error defined: MTU
   exceeded.  As part of DTLS session establishment, the CAPWAP
   component informs the DTLS component of the MTU size.  This may be
   dynamically modified at any time when the CAPWAP component sends the
   DTLSMtuUpdate command to the DTLS component (see Section 2.3.2.1).
   The value provided to the DTLS stack is the result of the MTU
   Discovery process, which is described in Section 3.5.  The DTLS
   component returns this notification to the CAPWAP component whenever
   a transmission request will result in a packet which exceeds the MTU.

2.4.4.  DTLS EndPoint Authentication and Authorization

   DTLS supports endpoint authentication with certificates or preshared
   keys.  The TLS algorithm suites for each endpoint authentication
   method are described below.

2.4.4.1.  Authenticating with Certificates

   Note that only block ciphers are currently recommended for use with
   DTLS.  To understand the reasoning behind this, see [21].  At
   present, the following algorithms MUST be supported when using
   certificates for CAPWAP authentication:

   o  TLS_RSA_WITH_AES_128_CBC_SHA

   The following algorithms SHOULD be supported when using certificates:



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   o  TLS_DH_RSA_WITH_AES_128_CBC_SHA

   The following algorithms MAY be supported when using certificates:

   o  TLS_RSA_WITH_AES_256_CBC_SHA

   o  TLS_DH_RSA_WITH_AES_256_CBC_SHA

2.4.4.2.  Authenticating with Preshared Keys

   Pre-shared keys present significant challenges from a security
   perspective, and for that reason, their use is strongly discouraged.
   Several methods for authenticating with preshared keys are defined
   [6], and we focus on the following two:

   o  PSK key exchange algorithm - simplest method, ciphersuites use
      only symmetric key algorithms

   o  DHE_PSK key exchange algorithm - use a PSK to authenticate a
      Diffie-Hellman exchange.  These ciphersuites give some additional
      protection against dictionary attacks and also provide Perfect
      Forward Secrecy (PFS).

   The first approach (plain PSK) is susceptible to passive dictionary
   attacks; hence, while this algorithm MUST be supported, special care
   should be taken when choosing that method.  In particular, user-
   readable passphrases SHOULD NOT be used, and use of short PSKs SHOULD
   be strongly discouraged.

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

   o  TLS_PSK_WITH_AES_128_CBC_SHA

   o  TLS_DHE_PSK_WITH_AES_128_CBC_SHA

   The following algorithms MAY be supported when using preshared keys:

   o  TLS_PSK_WITH_AES_256_CBC_SHA

   o  TLS_DHE_PSK_WITH_AES_256_CBC_SHA

2.4.4.3.  Certificate Usage

   Certificate authorization by the AC and WTP is required so that only
   an AC may perform the functions of an AC and that only a WTP may
   perform the functions of a WTP.  This restriction of functions to the
   AC or WTP requires that the certificates used by the AC MUST be



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   distinguishable from the certificate used by the WTP.  To accomplish
   this differentiation, the x.509 certificates MUST include the
   Extended Key Usage (EKU) certificate extension [4].

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

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

         KeyPurposeId  ::=  OBJECT IDENTIFIER


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

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

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

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



   For an AC, the id-kp-capwapAC EKU MUST be present in the certificate.
   For a WTP, the id-kp-capwapWTP EKU MUST be present in the
   certificate.  The id-kp-anyExtendedKeyUsage, if present, SHOULD be
   ignored.

   Part of the CAPWAP certificate validation process includes ensuring
   that the proper EKU is included and allowing the CAPWAP session to be
   established only if the extension properly represents the device.
   For instance, an AC SHOULD NOT accept a connection request from
   another AC, and therefore MUST verify that the id-kp-capwapWTP EKU is
   present in the certificate.

   CAPWAP implementations MUST support certificates where the common
   name (CN) for both the WTP and AC is the MAC address of that device.
   The MAC address MUST be formatted as ASCII HEX, e.g.
   01:23:45:67:89:ab.  Note that the CN field MAY contain either of the
   EUI-48 [22] or EUI-64 [23] MAC Address formats.

   ACs and WTPs MUST authorize (e.g. through access control lists)
   certificates of devices to which they are connecting, e.g., based on



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   the issuer, MAC address, or organizational information specified in
   the certificate.  The identities specified in the certificates bind a
   particular DTLS session to a specific pair of mutually-authenticated
   and authorized MAC addresses.  The particulars of authorization
   filter construction are implementation details which are, for the
   most part, not within the scope of this specification.  However, at
   minimum, all devices MUST verify that the appropriate EKU bit is set
   according to the role of the peer device (AC vs. WTP), and that the
   issuer of the certificate is appropriate for the domain in question.

2.4.4.4.  PSK Usage

   When DTLS uses PSK Ciphersuites, the ServerKeyExchange message MUST
   contain the "PSK identity hint" field and the ClientKeyExchange
   message MUST contain the "PSK identity" field.  These fields are used
   to help the WTP select the appropriate PSK for use with the AC, and
   then indicate to the AC which key is being used.  When PSKs are
   provisioned to WTPs and ACs, both the PSK Hint and PSK Identity for
   the key MUST be specified.

   The PSK Hint SHOULD uniquely identify the AC and the PSK Identity
   SHOULD uniquely identify the WTP.  It is RECOMMENDED that these hints
   and identities be the ASCII HEX-formatted MAC addresses of the
   respective devices, since each pairwise combination of WTP and AC
   SHOULD have a unique PSK.  The PSK hint and identity SHOULD be
   sufficient to perform authorization, as simply having knowledge of a
   PSK does not necessarily imply authorization.

   If a single PSK is being used for multiple devices on a CAPWAP
   network, which is NOT RECOMMENDED, the PSK Hint and Identity can no
   longer be a MAC address, so appropriate hints and identities SHOULD
   be selected to identify the group of devices to which the PSK is
   provisioned.


















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3.  CAPWAP Transport

   Communication between a WTP and an AC is established using the
   standard UDP client/server model.  The CAPWAP protocol supports both
   UDP and UDP-Lite [11] transport protocols.  When run over IPv4, UDP
   is used for the CAPWAP control and data channels.

   When run over IPv6, the CAPWAP control channel always uses UDP, while
   the CAPWAP data channel may use either UDP or UDP-Lite.  UDP-Lite is
   the default transport protocol for the CAPWAP data channel.  However,
   if a middlebox or IPv4 to IPv6 gateway has been discovered, UDP is
   used for the CAPWAP data channel.

   This section describes how the CAPWAP protocol is carried over IP and
   UDP/UDP-Lite transport protocols.  The CAPWAP Transport Protocol
   message element Section 4.6.15 describes the rules to use in
   determining which transport protocol is to be used.

3.1.  UDP Transport

   One of the CAPWAP protocol requirements is to allow a WTP to reside
   behind a middlebox, firewall and/or Network Address Translation (NAT)
   device.  Since a CAPWAP session is initiated by the WTP (client) to
   the well-known UDP port of the AC (server), the use of UDP is a
   logical choice.  The UDP checksum field in CAPWAP packets MUST be set
   to zero.

   CAPWAP protocol control packets sent from the WTP to the AC use the
   CAPWAP control channel, as defined in Section 1.4.  The CAPWAP
   control port at the AC is the well known UDP port [to be IANA
   assigned].  The CAPWAP control port at the WTP can be any port
   selected by the WTP.

   CAPWAP protocol data packets sent from the WTP to the AC use the
   CAPWAP data channel, as defined in Section 1.4.  The CAPWAP data port
   at the AC is the well known UDP port [to be IANA assigned].  The
   CAPWAP data port at the WTP can be any port selected by the WTP.

3.2.  UDP-Lite Transport

   When CAPWAP is run over IPv6, UDP-Lite is the default transport
   protocol, which reduces the checksum processing required for each
   packet (compared to the use of UDP over IPv6 [13]).  When UDP-Lite is
   used, the checksum field MUST have a coverage of 8 [11].

   UDP-Lite uses the same port assignments as UDP.





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3.3.  AC Discovery

   The AC discovery phase allows the WTP to determine which ACs are
   available, and chose the best AC with which to establish a CAPWAP
   session.  The discovery phase occurs when the WTP enters the optional
   Discovery state.  A WTP does not need to complete the AC Discovery
   phase if it uses a pre-configured AC.  This section details the
   mechanism used by a WTP to dynamically discover candidate ACs.

   A WTP and an AC will frequently not reside in the same IP subnet
   (broadcast domain).  When this occurs, the WTP must be capable of
   discovering the AC, without requiring that multicast services are
   enabled in the network.

   When the WTP attempts to establish communication with an AC, it sends
   the Discovery Request message and receives the Discovery Response
   message from the AC(s).  The WTP MUST send the Discovery Request
   message to either the limited broadcast IP address (255.255.255.255),
   a well known multicast address or to the unicast IP address of the
   AC.  For IPv6 networks, since broadcast does not exist, the use of
   "All ACs multicast address" is used instead.  Upon receipt of the
   Discovery Request message, the AC sends a Discovery Response message
   to the unicast IP address of the WTP, regardless of whether the
   Discovery Request message was sent as a broadcast, multicast or
   unicast message.

   WTP use of a limited IP broadcast, multicast or unicast IP address is
   implementation dependent.

   When a WTP transmits a Discovery Request message to a unicast
   address, the WTP must first obtain the IP address of the AC.  Any
   static configuration of an AC's IP address on the WTP non-volatile
   storage is implementation dependent.  However, additional dynamic
   schemes are possible, for example:

   DHCP:  See [17] for more information on the use of DHCP to discover
      AC IP addresses.

   DNS:  The DNS name "CAPWAP-AC-Address" MAY be resolvable to one or
      more AC addresses.

   An AC MAY also communicate alternative ACs to the WTP within the
   Discovery Response message through the AC IPv4 List (see
   Section 4.6.2) and AC IPv6 List (see Section 4.6.2).  The addresses
   provided in these two message elements are intended to help the WTP
   discover additional ACs through means other than those listed above.

   The AC Name with Index message element (see Section 4.6.5), is used



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   to communicate a list of preferred ACs to the WTP.  The WTP SHOULD
   attempt to utilize the ACs listed in the order provided by the AC.
   The Name to IP Address mapping is handled via the Discovery message
   exchange, in which the ACs provide their identity in the AC Name (see
   Section 4.6.4) message element in the Discovery Response message.

   Once the WTP has received Discovery Response messages from the
   candidate ACs, it MAY use other factors to determine the preferred
   AC.  For instance, each binding defines a WTP Radio Information
   message element (see Section 2.1), which the AC includes in Discovery
   Response messages.  The presence of one or more of these message
   elements is used to identify the CAPWAP bindings supported by the AC.
   A WTP MAY connect to an AC based on the supported bindings
   advertised.

3.4.  Fragmentation/Reassembly

   While fragmentation and reassembly services are provided by IP, the
   CAPWAP protocol also provides such services.  Environments where the
   CAPWAP protocol is used involve firewall, NAT and "middle box"
   devices, which tend to drop IP fragments to minimize possible DoS
   attacks.  By providing fragmentation and reassembly at the
   application layer, any fragmentation required due to the tunneling
   component of the CAPWAP protocol becomes transparent to these
   intermediate devices.  Consequently, the CAPWAP protocol can be used
   in any network configuration.

3.5.  MTU Discovery

   Once a WTP has discovered the AC it wishes to establish a CAPWAP
   session with, it SHOULD perform a Path MTU (PMTU) discovery.  The MTU
   discovered is used to configure the DTLS component (see
   Section 2.3.2.1), while non-DTLS frames need to be fragmented to fit
   the MTU, defined in Section 3.4.  The procedures described in [14],
   for IPv4, or [15], for IPv6 SHOULD be used.  Alternatively,
   implementers MAY use the procedures defined in [12].  The WTP SHOULD
   also periodically re-evaluate the MTU using the guidelines provided
   in these two RFCs.













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4.  CAPWAP Packet Formats

   This section contains the CAPWAP protocol packet formats.  A CAPWAP
   protocol packet consists of one or more CAPWAP Transport Layer packet
   headers followed by a CAPWAP message.  The CAPWAP message can be
   either of type Control or Data, where Control packets carry
   signaling, and Data packets carry user payloads.  The CAPWAP frame
   formats for CAPWAP Data packets, and for DTLS encapsulated CAPWAP
   Data and Control packets are defined below.

   The CAPWAP Control protocol includes two messages that are never
   protected by DTLS: the Discovery Request message and the Discovery
   Response message.  These messages need to be in the clear to allow
   the CAPWAP protocol to properly identify and process them.  The
   format of these packets are as follows:

       CAPWAP Control Packet (Discovery Request/Response):
       +-------------------------------------------+
       | IP  | UDP | CAPWAP | Control | Message    |
       | Hdr | Hdr | Header | Header  | Element(s) |
       +-------------------------------------------+

   All other CAPWAP control protocol messages MUST be protected via the
   DTLS protocol, which ensures that the packets are both authenticated
   and encrypted.  These packets include the CAPWAP DTLS Header, which
   is described in Section 4.2.  The format of these packets is as
   follows:

    CAPWAP Control Packet (DTLS Security Required):
    +------------------------------------------------------------------+
    | IP  | UDP | CAPWAP   | DTLS | CAPWAP | Control| Message   | DTLS |
    | Hdr | Hdr | DTLS Hdr | Hdr  | Header | Header | Element(s)| Trlr |
    +------------------------------------------------------------------+
                           \---------- authenticated -----------/
                                  \------------- encrypted ------------/

   The CAPWAP protocol allows optional protection of data packets, using
   DTLS.  Use of data packet protection is determined by AC policy.
   When DTLS is utilized, the optional CAPWAP DTLS Header is present,
   which is described in Section 4.2.  The format of CAPWAP data packets
   is shown below:










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       CAPWAP Plain Text Data Packet :
       +-------------------------------+
       | IP  | UDP | CAPWAP | Wireless |
       | Hdr | Hdr | Header | Payload  |
       +-------------------------------+

       DTLS Secured CAPWAP Data Packet:
       +--------------------------------------------------------+
       | IP  | UDP |  CAPWAP  | DTLS | CAPWAP | Wireless | DTLS |
       | Hdr | Hdr | DTLS Hdr | Hdr  |  Hdr   | Payload  | Trlr |
       +--------------------------------------------------------+
                              \------ authenticated -----/
                                     \------- encrypted --------/

   UDP Header:  All CAPWAP packets are encapsulated within either UDP,
      or UDP-Lite when used over IPv6.  Section 3 defines the specific
      UDP or UDP-Lite usage.

   CAPWAP DTLS Header:  All DTLS encrypted CAPWAP protocol packets are
      prefixed with the CAPWAP DTLS header (see Section 4.2).

   DTLS Header:  The DTLS header provides authentication and encryption
      services to the CAPWAP payload it encapsulates.  This protocol is
      defined in RFC 4347 [8].

   CAPWAP Header:  All CAPWAP protocol packets use a common header that
      immediately follows the CAPWAP preamble or DTLS header.  The
      CAPWAP Header is defined in Section 4.3.

   Wireless Payload:  A CAPWAP protocol packet that contains a wireless
      payload is a CAPWAP data packet.  The CAPWAP protocol does not
      specify the format of the wireless payload, which is defined by
      the appropriate wireless standard.  Additional information is in
      Section 4.4.

   Control Header:  The CAPWAP protocol includes a signaling component,
      known as the CAPWAP control protocol.  All CAPWAP control packets
      include a Control Header, which is defined in Section 4.5.1.
      CAPWAP data packets do not contain a Control Header field.

   Message Elements:  A CAPWAP Control packet includes one or more
      message elements, which are found immediately following the
      Control Header.  These message elements are in a Type/Length/value
      style header, defined in Section 4.6.

   A CAPWAP implementation MUST be capable of receiving a reassembled
   CAPWAP message of length 4096 bytes.  A CAPWAP implementation MAY
   indicate that it supports a higher maximum message length, by



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   including the Maximum Message Length message element, see
   Section 4.6.32 in the Join Request message or the Join Response
   message.

4.1.  CAPWAP Preamble

   The CAPWAP preamble is common to all CAPWAP transport headers and is
   used to identify the header type that immediately follows.  The
   reason for this header is to avoid needing to perform byte
   comparisons in order to guess whether the frame is DTLS encrypted or
   not.  It also provides an extensibility framework that can be used to
   support additional transport types.  The format of the preamble is as
   follows:

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

   Version:  A 4 bit field which contains the version of CAPWAP used in
      this packet.  The value for this specification is zero (0).

   Payload Type:  A 4 bit field which specifies the payload type that
      follows the UDP header.  The following values are supported:

      0 -  CAPWAP Header.  The CAPWAP Header (see Section 4.3)
         immediately follows the UDP header.  If the packet is received
         on the CAPWAP data channel, the CAPWAP stack MUST treat the
         packet as a clear text CAPWAP data packet.  If received on the
         CAPWAP control channel, the CAPWAP stack MUST treat the packet
         as a clear text CAPWAP control packet.  If the control packet
         is not a Discovery Request or Discovery Response packet, the
         packet MUST be dropped.

      1 -  CAPWAP DTLS Header.  The CAPWAP DTLS Header, and DTLS packet,
         immediately follows the UDP header (see Section 4.2).

4.2.  CAPWAP DTLS Header

   The CAPWAP DTLS Header is used to identify the packet as a DTLS
   encrypted packet.  The first eight bits includes the common CAPWAP
   Preamble.  The remaining 24 bits are padding to ensure 4 byte
   alignment, and MAY be used in a future version of the protocol.  The
   DTLS packet [8] always immediately follows this header.  The format
   of the CAPWAP DTLS Header is as follows:





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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |CAPWAP Preamble|                    Reserved                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   CAPWAP Preamble:  The CAPWAP Preamble is defined in Section 4.1.  The
      CAPWAP Preamble's Payload Type field MUST be set to one (1).

   Reserved:  The 24-bit field is reserved for future use.  All
      implementations complying with this protocol MUST set to zero any
      bits that are reserved in the version of the protocol supported by
      that implementation.  Receivers MUST ignore all bits not defined
      for the version of the protocol they support.

4.3.  CAPWAP Header

   All CAPWAP protocol messages are encapsulated using a common header
   format, regardless of the CAPWAP Control or CAPWAP Data transport
   used to carry the messages.  However, certain flags are not
   applicable for a given transport.  Refer to the specific transport
   section in order to determine which flags are valid.

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

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |CAPWAP Preamble|  HLEN   |   RID   | WBID    |T|F|L|W|M|K|Flags|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Fragment ID          |     Frag Offset         |Rsvd |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 (optional) Radio MAC Address                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            (optional) Wireless Specific Information           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Payload ....                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   CAPWAP Preamble:  The CAPWAP Preamble is defined in Section 4.1.  The
      CAPWAP Preamble's Payload Type field MUST be set to zero (0).  If
      the CAPWAP DTLS Header is present, the version number in both
      CAPWAP Preambles MUST match.  The reason for this duplicate field
      is to avoid any possible tampering of the version field in the
      preamble which is not encrypted or authenticated.





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   HLEN:  A 5 bit field containing the length of the CAPWAP transport
      header in 4 byte words (Similar to IP header length).  This length
      includes the optional headers.

   RID:  A 5 bit field which contains the Radio ID number for this
      packet.  Given that MAC Addresses are not necessarily unique
      across physical radios in a WTP, the Radio Identifier (RID) field
      is used to indicate which physical radio the message is associated
      with.

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

      1 -  IEEE 802.11

      2 -  IEEE 802.16

      3 -  EPCGlobal

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

   F: The Fragment 'F' bit indicates whether this packet is a fragment.
      When this bit is one (1), the packet is a fragment and MUST be
      combined with the other corresponding fragments to reassemble the
      complete information exchanged between the WTP and AC.

   L: The Last 'L' bit is valid only if the 'F' bit is set and indicates
      whether the packet contains the last fragment of a fragmented
      exchange between WTP and AC.  When this bit is 1, the packet is
      the last fragment.  When this bit is 0, the packet is not the last
      fragment.

   W: The Wireless 'W' bit is used to specify whether the optional
      Wireless Specific Information field is present in the header.  A
      value of one (1) is used to represent the fact that the optional
      header is present.

   M: The M bit is used to indicate that the Radio MAC Address optional
      header is present.  This is used to communicate the MAC address of
      the receiving radio.







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   K: The 'Keep-alive' K bit indicates the packet is a Data Channel Keep
      Alive packet.  This packet is used to map the data channel to the
      control channel for the specified Session ID and to maintain
      freshness of the data channel.  The K bit MUST NOT be set for data
      packets containing user data.

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

   Fragment ID:  A 16 bit field whose value is assigned to each group of
      fragments making up a complete set.  The fragment ID space is
      managed individually for every WTP/AC pair.  The value of Fragment
      ID is incremented with each new set of fragments.  The Fragment ID
      wraps to zero after the maximum value has been used to identify a
      set of fragments.

   Fragment Offset:  A 13 bit field that indicates where in the payload
      this fragment belongs during re-assembly.  This field is valid
      when the 'F' bit is set to 1.  The fragment offset is measured in
      units of 8 octets (64 bits).  The first fragment has offset zero.
      Note the CAPWAP protocol does not allow for overlapping fragments.

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

   Radio MAC Address:  This optional field contains the MAC address of
      the radio receiving the packet.  This is useful in packets sent
      from the WTP to the AC, when the native wireless frame format is
      converted to 802.3 by the WTP.  This field is only present if the
      'M' bit is set.  The HLEN field assumes 4 byte alignment, and this
      field MUST be padded with zeroes (0x00) if it is not 4 byte
      aligned.

      The field contains the basic format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Length    |                  MAC Address
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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      Length:  The length of the MAC Address field [22] [23].

      MAC Address:  The MAC Address of the receiving radio.

   Wireless Specific Information:  This optional field contains
      technology specific information that may be used to carry per
      packet wireless information.  This field is only present if the
      'W' bit is set.  The WBID field in the CAPWAP header is used to
      identify the format of the wireless specific information optional
      field.  The HLEN field assumes 4 byte alignment, and this field
      MUST be padded with zeroes (0x00) if it is not 4 byte aligned.

      The Wireless Specific Information field uses the following format:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Length     |                Data...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Length:  The length of the data field

      Data:  Wireless specific information, defined by the wireless
         specific binding specified in the CAPWAP Header's WBID field.

   Payload:  This field contains the header for a CAPWAP Data Message or
      CAPWAP Control Message, followed by the data contained in the
      message.

4.4.  CAPWAP Data Messages

   There are two different types of CAPWAP data packets, CAPWAP Data
   Channel Keep Alive packets and Data Payload packets.  The first is
   used by the WTP to synchronize the control and data channels, and to
   maintain freshness of the data channel.  The second is used to
   transmit user payloads between the AC and WTP.  This section
   describes both types of CAPWAP data packet formats.

   Both CAPWAP data messages are transmitted on the CAPWAP data channel.

4.4.1.  CAPWAP Data Keepalive

   The CAPWAP Data Channel Keep Alive packet is used to bind the CAPWAP
   control channel with the data channel, and to maintain freshness of
   the data channel, ensuring that the channel is still functioning.
   The CAPWAP Data Channel Keep Alive packet is transmitted by the WTP
   when the DataChannelKeepAlive timer expires.  When the CAPWAP Data
   Channel Keep Alive packet is transmitted, the WTP sets the



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   DataChannelDeadInterval timer.

   In the CAPWAP Data Channel Keep Alive packet, all of the fields in
   the CAPWAP header, except the HLEN field and the K bit, are set to
   zero upon transmission.  Upon receiving a CAPWAP Data Channel Keep
   Alive packet, the AC transmits a CAPWAP Data Channel Keep Alive
   packet back to the WTP.  The contents of the transmitted packet are
   identical to the contents of the received packet.

   Upon receiving a CAPWAP Data Channel Keep Alive packet, the WTP
   cancels the DataChannelDeadInterval timer and resets the
   DataChannelKeepAlive timer.  The CAPWAP Data Channel Keep Alive
   packet is retransmitted by the WTP in the same manner as the CAPWAP
   control messages.  If the DataChannelDeadInterval timer expires, the
   WTP tears down the control DTLS session, and the data DTLS session if
   one existed.

   The CAPWAP Data Channel Keep Alive packet contains the following
   payload immediately following the CAPWAP Header (see Section 4.3)

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Message Element Length     |  Message Element [0..N] ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message Element Length:   The Length field indicates the number of
      bytes following the CAPWAP Header.

   Message Element[0..N]:   The message element(s) carry the information
      pertinent to each of the CAPWAP Data Keepalive message.  The
      following message elements MUST be present in this CAPWAP message:

         Session ID, see Section 4.6.37

4.4.2.  Data Payload

   A CAPWAP protocol Data Payload packet encapsulates a forwarded
   wireless frame.  The CAPWAP protocol defines two different modes of
   encapsulation; IEEE 802.3 and native wireless.  IEEE 802.3
   encapsulation requires that for 802.11 frames, the 802.11
   *Integration* function be performed in the WTP.  An IEEE 802.3
   encapsulated user payload frame has the following format:

       +------------------------------------------------------+
       | IP Header | UDP Header | CAPWAP Header | 802.3 Frame |
       +------------------------------------------------------+




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   The CAPWAP protocol also defines the native wireless encapsulation
   mode.  The format of the encapsulated CAPWAP data frame is subject to
   the rules defined by the specific wireless technology binding.  Each
   wireless technology binding MUST contain a section entitled "Payload
   Encapsulation", which defines the format of the wireless payload that
   is encapsulated within CAPWAP Data packets.

   For 802.3 payload frames, the 802.3 frame is encapsulated (excluding
   the IEEE 802.3 FCS checksum).  If the encapsulated frame would exceed
   the transport layer's MTU, the sender is responsible for
   fragmentation of the frame, as specified in Section 3.4.

4.4.3.  Establishment of a DTLS Data Channel

   If the AC and WTP are configured to tunnel the data channel over
   DTLS, the proper DTLS session must be initiated.  To avoid having to
   reauthenticate and reauthorize an AC and WTP, the DTLS data channel
   MUST be initiated using the TLS session resumption feature [7].

   When establishing the DTLS-encrypted data channel, the WTP MUST
   provide the identifier returned during the initialization of the
   control channel to the DTLS component so it can perform the
   resumption using the proper session information.

   The AC DTLS implementation MUST NOT accept a session resumption
   request for a DTLS session in which the control channel for the
   session has been torn down.

4.5.  CAPWAP Control Messages

   The CAPWAP Control protocol provides a control channel between the
   WTP and the AC.  Control messages are divided into the following
   message types:

   Discovery:  CAPWAP Discovery messages are used to identify potential
      ACs, their load and capabilities.

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

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

   WTP Configuration Management:  The WTP Configuration messages are
      used by the AC to deliver a specific configuration to the WTP.
      Messages which retrieve statistics from a WTP are also included in
      WTP Configuration Management.




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   Station Session Management:  Station Session Management messages are
      used by the AC to deliver specific station policies to the WTP.

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

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

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

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

4.5.1.  Control Message Format

   All CAPWAP control messages are sent encapsulated within the CAPWAP
   header (see Section 4.3).  Immediately following the CAPWAP header,
   is the control header, which has the following format:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Message Type                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Seq Num    |        Msg Element Length     |     Flags     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Msg Element [0..N] ...
     +-+-+-+-+-+-+-+-+-+-+-+-+

4.5.1.1.  Message Type

   The Message Type field identifies the function of the CAPWAP control
   message.  The Message Type field is comprised of an IANA Enterprise
   Number and an enterprise specific message type number.  The first
   three octets contain the enterprise number in network byte order,
   with zero used for CAPWAP protocol defined message types and the IEEE
   802.11 IANA assigned enterprise number 13277 is used for IEEE 802.11
   technology specific message types.  The last octet is the enterprise
   specific message type number, which has a range from 0 to 255.



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   The message type field is defined as:

         Message Type =
                 IANA Enterprise Number * 256 +
                     Enterprise Specific Message Type Number

   The CAPWAP protocol reliability mechanism requires that messages be
   defined in pairs, consisting of both a Request and a Response
   message.  The Response message MUST acknowledge the Request message.
   The assignment of CAPWAP control Message Type Values always occurs in
   pairs.  All Request messages have odd numbered Message Type Values,
   and all Response messages have even numbered Message Type Values.
   The Request value MUST be assigned first.  As an example, assigning a
   Message Type Value of 3 for a Request message and 4 for a Response
   message is valid, while assigning a Message Type Value of 4 for a
   Response message and 5 for the corresponding Request message is
   invalid.

   When a WTP or AC receives a message with a Message Type Value field
   that is not recognized and is an odd number, the number in the
   Message Type Value Field is incremented by one, and a Response
   message with a Message Type Value field containing the incremented
   value and containing the Result Code message element with the value
   (Unrecognized Request) is returned to the sender of the received
   message.  If the unknown message type is even, the message is
   ignored.

   The valid values for CAPWAP Control Message Types are specified in
   the table below:






















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           CAPWAP Control Message           Message Type
                                              Value
           Discovery Request                    1
           Discovery Response                   2
           Join Request                         3
           Join Response                        4
           Configuration Status                 5
           Configuration Status Response        6
           Configuration Update Request         7
           Configuration Update Response        8
           WTP Event Request                    9
           WTP Event Response                  10
           Change State Event Request          11
           Change State Event Response         12
           Echo Request                        13
           Echo Response                       14
           Image Data Request                  15
           Image Data Response                 16
           Reset Request                       17
           Reset Response                      18
           Primary Discovery Request           19
           Primary Discovery Response          20
           Data Transfer Request               21
           Data Transfer Response              22
           Clear Configuration Request         23
           Clear Configuration Response        24
           Station Configuration Request       25
           Station Configuration Response      26

4.5.1.2.  Sequence Number

   The Sequence Number Field is an identifier value used to match
   Request and Response packets.  When a CAPWAP packet with a Request
   Message Type Value is received, the value of the Sequence Number
   field is copied into the corresponding Response message.

   When a CAPWAP control message is sent, the sender's internal sequence
   number counter is monotonically incremented, ensuring that no two
   pending Request messages have the same Sequence Number.  The Sequence
   Number field wraps back to zero.

4.5.1.3.  Message Element Length

   The Length field indicates the number of bytes following the Sequence
   Number field.






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4.5.1.4.  Flags

   The Flags field MUST be set to zero.

4.5.1.5.  Message Element[0..N]

   The message element(s) carry the information pertinent to each of the
   control message types.  Every control message in this specification
   specifies which message elements are permitted.

   When a WTP or AC receives a CAPWAP message without a message element
   that is specified as mandatory for the CAPWAP message, then the
   CAPWAP message is discarded.  If the received message was a Request
   message for which the corresponding Response message carries message
   elements, then a corresponding Response message with a Result Code
   message element indicating "Failure - Missing Mandatory Message
   Element" is returned to the sender.

   When a WTP or AC receives a CAPWAP message with a message element
   that the WTP or AC does not recognize, the CAPWAP message is
   discarded.  If the received message was a Request message for which
   the corresponding Response message carries message elements, then a
   corresponding Response message with a Result Code message element
   indicating "Failure - Unrecognized Message Element" and one or more
   Returned Message Element message elements is included, containing the
   unrecognized message element(s).

4.5.2.  Control Message Quality of Service

   It is recommended that CAPWAP control messages be sent by both the AC
   and the WTP with an appropriate Quality of Service precedence value,
   ensuring that congestion in the network minimizes occurrences of
   CAPWAP control channel disconnects.  Therefore, a Quality of Service
   enabled CAPWAP device SHOULD use the following values:

   802.1P:   The precedence value of 7 SHOULD be used.

   DSCP:   The DSCP tag value of 46 SHOULD be used.

4.5.3.  Retransmissions

   The CAPWAP control protocol operates as a reliable transport.  For
   each Request message, a Response message is defined, which is used to
   acknowledge receipt of the Request message.  In addition, the control
   header Sequence Number field is used to pair the Request and Response
   messages (see Section 4.5.1).

   Response messages are not explicitly acknowledged, therefore if a



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   Response message is not received, the original Request message is
   retransmitted.  Implementations MAY cache Response messages to
   respond to a retransmitted Request messages with minimal local
   processing.  Retransmitted Request messages MUST NOT be altered by
   the sender.  The sender MUST assume that the original Request message
   was processed, but that the Response message was lost.  Any
   alterations to the original Request message MUST have a new Sequence
   Number, and be treated as a new Request message by the receiver.

   After transmitting a Request message, the RetransmitInterval (see
   Section 4.7) timer and MaxRetransmit (see Section 4.8) variable are
   used to determine if the original Request message needs to be
   retransmitted.  The RetransmitInterval timer is used the first time
   the Request is retransmitted.  The timer is then doubled every
   subsequent time the same Request message is retransmitted, up to
   MaxRetransmit but no more than half the EchoInterval timer (see
   Section 4.7.7).  Response messages are not subject to these timers.

   When a Request message is retransmitted, it MUST be re-encrypted via
   the DTLS stack.  If the peer had received the Request message, and
   the corresponding Response message was lost, it is necessary to
   ensure that retransmitted Request messages are not identified as
   replays by the DTLS stack.  Similarly, any cached Response messages
   that are retransmitted as a result of receiving a retransmitted
   Request message MUST be re-encrypted via DTLS.

   Duplicate Response messages, identified by the Sequence Number field
   in the CAPWAP control message header, SHOULD be discarded upon
   receipt.

4.6.  CAPWAP Protocol Message Elements

   This section defines the CAPWAP Protocol message elements which are
   included in CAPWAP protocol control messages.

   Message elements are used to carry information needed in control
   messages.  Every message element is identified by the Type Value
   field, defined below.  The total length of the message elements is
   indicated in the message element Length field.

   All of the message element definitions in this document use a diagram
   similar to the one below in order to depict its format.  Note that to
   simplify this specification, these diagrams do not include the header
   fields (Type and Length).  The header field values are defined in the
   message element descriptions.

   Unless otherwise specified, a control message that lists a set of
   supported (or expected) message elements MUST not expect the message



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   elements to be in any specific order.  The sender MAY include the
   message elements in any order.  Unless otherwise noted, one message
   element of each type is present in a given control message.

   Additional message elements may be defined in separate IETF
   documents.

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

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Value ...   |
     +-+-+-+-+-+-+-+-+

   The 16 bit Type field identifies the information carried in the Value
   field and Length (16 bits) indicates the number of bytes in the Value
   field.  Type field values are allocated as follows:

              Usage                              Type Values

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

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

   CAPWAP Message Element                            Type Value

   AC Descriptor                                         1
   AC IPv4 List                                          2
   AC IPv6 List                                          3
   AC Name                                               4
   AC Name with Index                                    5
   AC Timestamp                                          6
   Add MAC ACL Entry                                     7
   Add Station                                           8
   Add Static MAC ACL Entry                              9
   CAPWAP Control IPV4 Address                          10
   CAPWAP Control IPV6 Address                          11
   CAPWAP Local IPV4 Address                            TBD
   CAPWAP Local IPV6 Address                            TBD
   CAPWAP Timers                                        12



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   CAPWAP Transport Protocol                            TBD
   Data Transfer Data                                   13
   Data Transfer Mode                                   14
   Decryption Error Report                              15
   Decryption Error Report Period                       16
   Delete MAC ACL Entry                                 17
   Delete Station                                       18
   Delete Static MAC ACL Entry                          19
   Discovery Type                                       20
   Duplicate IPv4 Address                               21
   Duplicate IPv6 Address                               22
   Idle Timeout                                         23
   Image Data                                           24
   Image Identifier                                     25
   Image Info                                           26
   Initiate Download                                    27
   Location Data                                        28
   Maximum Message Length                               29
   Radio Administrative State                           31
   Radio Operational State                              32
   Result Code                                          33
   Returned Message Element                             34
   Session ID                                           35
   Statistics Timer                                     36
   Vendor Specific Payload                              37
   WTP Board Data                                       38
   WTP Descriptor                                       39
   WTP Fallback                                         40
   WTP Frame Tunnel Mode                                41
   WTP IPv4 IP Address                                  42
   WTP IPv6 IP Address                                  43
   WTP MAC Type                                         44
   WTP Name                                             45
   WTP Operational Statistics                           46
   WTP Radio Statistics                                 47
   WTP Reboot Statistics                                48
   WTP Static IP Address Information                    49


4.6.1.  AC Descriptor

   The AC Descriptor message element is used by the AC to communicate
   its current state.  The value contains the following fields.








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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            Stations           |             Limit             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Active WTPs          |            Max WTPs           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Security   |  R-MAC Field  |   Reserved1   |  DTLS Policy  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=4                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=5                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   1 for AC Descriptor

   Length:   >= 12

   Stations:   The number of stations currently served by the AC

   Limit:   The maximum number of stations supported by the AC

   Active WTPs:   The number of WTPs currently attached to the AC

   Max WTPs:   The maximum number of WTPs supported by the AC

   Security:   A 8 bit mask specifying the authentication credential
      type supported by the AC.  The following values are supported (see
      Section 2.4.4):

      1 -  X.509 Certificate Based

      2 -  Pre-Shared Secret

   R-MAC Field:   The AC supports the optional Radio MAC Address field
      in the CAPWAP transport Header (see Section 4.3).






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

   DTLS Policy:   The AC communicates its policy on the use of DTLS for
      the CAPWAP data channel.  The AC MAY communicate more than one
      supported option, represented by the bit field below.  The WTP
      MUST abide by one of the options communicated by AC.  The
      following bit field values are supported:

      1 -  Clear Text Data Channel Supported

      2 -  DTLS Enabled Data Channel Supported

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

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

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

      5 - Software Version:   The AC's Software (firmware) version
         number.

   Length:   Length of vendor specific encoding of AC information.

   Value:   Vendor specific encoding of AC information.

4.6.2.  AC IPv4 List

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


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       AC IP Address[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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   Type:   2 for AC IPv4 List

   Length:   >= 4

      The AC IP Address: An array of 32-bit integers containing AC IPv4
      Addresses.

4.6.3.  AC IPv6 List

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


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       AC IP Address[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       AC IP Address[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       AC IP Address[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       AC IP Address[]                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   3 for AC IPV6 List

   Length:   >= 16

      The AC IP Address: An array of 128-bit integers containing AC IPv6
      Addresses.

4.6.4.  AC Name

   The AC Name message element contains an UTF-8 representation of the
   AC identity.  The value is a variable length byte string.  The string
   is NOT zero terminated.

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







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   Type:   4 for AC Name

   Length:   > 0

   Name:   A variable length UTF-8 encoded string containing the AC's
      name

4.6.5.  AC Name with Index

   The AC Name with Index message element is sent by the AC to the WTP
   to configure preferred ACs.  The number of instances of this message
   element is equal to the number of ACs configured on the WTP.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Index     |   AC Name...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   5 for AC Name with Index

   Length:   > 2

   Index:   The index of the preferred server (1=primary, 2=secondary).

   AC Name:   A variable length UTF-8 encoded string containing the AC
      name.

4.6.6.  AC Timestamp

   The AC Timestamp message element is sent by the AC to synchronize the
   WTP clock.

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

   Type:   6 for AC Timestamp

   Length:   4

   Timestamp:   The AC's current time, allowing all of the WTPs to be
      time synchronized in the format defined by Network Time Protocol
      (NTP) in RFC 1305 [3].





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4.6.7.  Add MAC ACL Entry

   The Add MAC Access Control List (ACL) Entry message element is used
   by an AC to add a MAC ACL list entry on a WTP, ensuring that the WTP
   no longer provides service to the MAC addresses provided in the
   message.  The MAC Addresses provided in this message element are not
   expected to be saved in non-volatile memory on the WTP.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Num of Entries|    Length     |         MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   7 for Add MAC ACL Entry

   Length:   >= 8

   Num of Entries:   The number of instances of the Type/MAC Addresses
      fields in the array.

   Length:  The length of the MAC Address field.

   MAC Address:   MAC Addresses to add to the ACL.

4.6.8.  Add Station

   The Add Station message element is used by the AC to inform a WTP
   that it should forward traffic for a station.  The Add Station
   message element is accompanied by technology specific binding
   information element(s) which may include security parameters.
   Consequently, the security parameters MUST be applied by the WTP for
   the station.

   After station policy has been delivered to the WTP through the Add
   Station message element, an AC MAY change any policies by sending a
   modified Add Station message element.  When a WTP receives an Add
   Station message element for an existing station, it MUST override any
   existing state for the station.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Radio ID   |     Length    |          MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  VLAN Name...
     +-+-+-+-+-+-+-+-+




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   Type:   8 for Add Station

   Length:   >= 8

   Radio ID:   An 8-bit value representing the radio

   Length:  The length of the MAC Address field.

   MAC Address:   The station's MAC Address

   VLAN Name:   An optional variable length UTF-8 encoded string
      containing the VLAN Name on which the WTP is to locally bridge
      user data.  Note this field is only valid with WTPs configured in
      Local MAC mode.

4.6.9.  Add Static MAC ACL Entry

   The Add Static MAC ACL Entry message element is used by an AC to add
   a permanent ACL entry on a WTP, ensuring that the WTP no longer
   provides any service to the MAC addresses provided in the message.
   The MAC Addresses provided in this message element are expected to be
   saved in non-volatile memory on the WTP.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Num of Entries|     Length    |          MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   9 for Add Static MAC ACL Entry

   Length:   >= 8

   Num of Entries:   The number of instances of the Type/MAC Addresses
      fields in the array.

   Length:  The length of the MAC Address field.

   MAC Address:   MAC Addresses to add to the permanent ACL.

4.6.10.  CAPWAP Control IPv4 Address

   The CAPWAP Control IPv4 Address message element is sent by the AC to
   the WTP during the discovery process and is used by the AC to provide
   the interfaces available on the AC, and the current number of WTPs
   connected.  When multiple CAPWAP Control IPV4 Address message
   elements are returned, the WTP SHOULD perform load balancing across
   the multiple interfaces.



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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           WTP Count           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   10 for CAPWAP Control IPv4 Address

   Length:   6

   IP Address:   The IP Address of an interface.

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

4.6.11.  CAPWAP Control IPv6 Address

   The CAPWAP Control IPv6 Address message element is sent by the AC to
   the WTP during the discovery process and is used by the AC to provide
   the interfaces available on the AC, and the current number of WTPs
   connected.  This message element is useful for the WTP to perform
   load balancing across multiple interfaces.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           WTP Count           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   11 for CAPWAP Control IPv6 Address

   Length:   18

   IP Address:   The IP Address of an interface.

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






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4.6.12.  CAPWAP Local IPv4 Address

   The CAPWAP Local IPv4 Address message element is sent by either the
   WTP or the AC in the Join Request, Configuration Status Request or
   Image Data Request message in order to communicate the IP Address of
   the transmitter.  The receiver uses this to determine whether a
   middlebox exists between the two peers, by comparing the source IP
   address of the packet against the value of the message element.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   TBD for CAPWAP Local IPv4 Address

   Length:   4

   IP Address:   The IP Address of the sender.

4.6.13.  CAPWAP Local IPv6 Address

   The CAPWAP Local IPv6 Address message element is sent by either the
   WTP or the AC in the Discovery Response or Join Request in order to
   communicate the IP Address of the transmitter.  The receiver uses
   this to determine whether a middlebox exists between the two peers,
   by comparing the source IP address of the packet against the value of
   the message element.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           IP Address                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   TBD for CAPWAP Local IPv6 Address

   Length:   16






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   IP Address:   The IP Address of the sender.

4.6.14.  CAPWAP Timers

   The CAPWAP Timers message element is used by an AC to configure
   CAPWAP timers on a WTP.

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Discovery   | Echo Request  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   12 for CAPWAP Timers

   Length:   2

   Discovery:   The number of seconds between CAPWAP Discovery messages,
      when the WTP is in the discovery phase.

   Echo Request:   The number of seconds between WTP Echo Request CAPWAP
      messages.  The default value for this message element is specified
      in Section 4.7.7.

4.6.15.  CAPWAP Transport Protocol

   When CAPWAP is run over IPv6, the UDP-Lite or UDP transports MAY be
   used (see Section 3).  The CAPWAP IPv6 Transport Protocol message
   element is used by either the WTP or the AC to signal which transport
   protocol is to be used for the CAPWAP data channel.

   Upon receiving the Join Request, the AC MAY set the CAPWAP Transport
   Protocol to UDP-Lite in the Configuration Status Request or Image
   Data Request message if the CAPWAP message was received over IPv6,
   and the CAPWAP Local IPv6 Address message element (see
   Section 4.6.13) is present and the address matches the packet's
   source IP address.

   Upon receiving the Configuration Status Request or Image Data Request
   message, the WTP MAY set the CAPWAP Transport Protocol to UDP-Lite in
   the Configuration Status Response or Image Data Response message if
   the message was received over IPv6, and the CAPWAP Local IPv6 Address
   message element (see Section 4.6.13) is present and the address
   matches the packet's source IP address.

   For any other condition, the CAPWAP Transport Protocol MUST be set to
   UDP.




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      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |   Transport   |
     +-+-+-+-+-+-+-+-+

   Type:   TBD for CAPWAP Transport Protocol

   Length:   1

   Transport:   The transport to use for the CAPWAP data channel.

      1 -  UDP-Lite The UDP-Lite transport protocol is to be used for
         the CAPWAP data channel.  Note that this option is illegal is
         either the WTP or the AC uses IPv4.

      2 -  UDP The UDP transport protocol is to be used for the CAPWAP
         data channel.

4.6.16.  Data Transfer Data

   The Data Transfer Data message element is used by the WTP to provide
   information to the AC for debugging purposes.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Data Type   |  Data Length  |    Data ....
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   13 for Data Transfer Data

   Length:   >= 3

   Data Type:   An 8-bit value the type of information being sent.  The
      following values are supported:

      1 -  WTP Crash Data

      2 -  WTP Memory Dump

   Data Length:   Length of data field.

   Data:   Debug information.







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4.6.17.  Data Transfer Mode

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

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

   Type:   14 for Data Transfer Mode

   Length:   1

   Data Type:   An 8-bit value the type of information being requested.
      The following values are supported:

      1 -  WTP Crash Data

      2 -  WTP Memory Dump

4.6.18.  Decryption Error Report

   The Decryption Error Report message element value is used by the WTP
   to inform the AC of decryption errors that have occurred since the
   last report.  Note that this error reporting mechanism is not used if
   encryption and decryption services are provided in the AC.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID    |Num Of Entries |     Length    | MAC Address...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   15 for Decryption Error Report

   Length:   >= 9

   Radio ID:   The Radio Identifier refers to an interface index on the
      WTP.

   Num of Entries:   The number of instances of the Type/MAC Addresses
      fields in the array.






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   Length:  The length of the MAC Address field.

   MAC Address:   MAC addresses of the station that has caused
      decryption errors.

4.6.19.  Decryption Error Report Period

   The Decryption Error Report Period message element value is used by
   the AC to inform the WTP how frequently it should send decryption
   error report messages.  Note that this error reporting mechanism is
   not used if encryption and decryption services are provided in the
   AC.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID    |        Report Interval        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   16 for Decryption Error Report Period

   Length:   3

   Radio ID:   The Radio Identifier refers to an interface index on the
      WTP.

   Report Interval:   A 16-bit unsigned integer indicating the time, in
      seconds.  The default value for this message element can be found
      in Section 4.8.8.

4.6.20.  Delete MAC ACL Entry

   The Delete MAC ACL Entry message element is used by an AC to delete a
   MAC ACL entry on a WTP, ensuring that the WTP provides service to the
   MAC addresses provided in the message.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Num of Entries|     Length    |          MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   17 for Delete MAC ACL Entry

   Length:   >= 8






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   Num of Entries:   The number of instances of the Type/MAC Addresses
      fields in the array.

   Length:  The length of the MAC Address field.

   MAC Address:   An array of MAC Addresses to delete from the ACL.

4.6.21.  Delete Station

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

   The transmission of a Delete Station message element could occur for
   various reasons, including for administrative reasons, or if the
   station has roamed to another WTP.

   The Delete Station message element MAY be sent by the WTP, in the WTP
   Event Request message, to inform the AC that a particular station is
   no longer being provided service.  This could occur as a result of an
   Idle Timeout (see section 4.4.43), due to internal resource shortages
   or for some other reason.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Radio ID   |     Length    |        MAC Address...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   18 for Delete Station

   Length:   >= 8

   Radio ID:   An 8-bit value representing the radio

   Length:  The length of the MAC Address field.

   MAC Address:   The station's MAC Address

4.6.22.  Delete Static MAC ACL Entry

   The Delete Static MAC ACL Entry message element is used by an AC to
   delete a previously added static MAC ACL entry on a WTP, ensuring
   that the WTP provides service to the MAC addresses provided in the
   message.





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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Num of Entries|     Length    |         MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   19 for Delete Static MAC ACL Entry

   Length:   >= 8

   Num of Entries:   The number of instances of the Type/MAC Addresses
      fields in the array.

   Length:  The length of the MAC Address field.

   MAC Address:   An array of MAC Addresses to delete from the static
      MAC ACL entry.

4.6.23.  Discovery Type

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

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

   Type:   20 for Discovery Type

   Length:   1

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

      0 -  Unknown

      1 -  Static Configuration

      2 -  DHCP

      3 -  DNS







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      4 -  AC Referral (used when the AC was configured either through
         the AC IPv4 List or AC IPv6 List message element)

4.6.24.  Duplicate IPv4 Address

   The Duplicate IPv4 Address message element is used by a WTP to inform
   an AC that it has detected another IP device using the same IP
   address that the WTP is currently using.

   The WTP MUST transmit this message element with the status set to 1
   after it has detected a duplicate IP address.  When the WTP detects
   that the duplicate IP address has been cleared, it MUSY send this
   message element with the status set to 0.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Status    |     Length    |          MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   21 for Duplicate IPv4 Address

   Length:   >= 12

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

   Status:   The status of the duplicate IP address.  The value MUST be
      set to 1 when a duplicate address is detected, and 0 when the
      duplicate address has been cleared.

   Length:  The length of the MAC Address field.

   MAC Address:   The MAC Address of the offending device.

4.6.25.  Duplicate IPv6 Address

   The Duplicate IPv6 Address message element is used by a WTP to inform
   an AC that it has detected another host using the same IP address
   that the WTP is currently using.

   The WTP MUST transmit this message element with the status set to 1
   after it has detected a duplicate IP address.  When the WTP detects
   that the duplicate IP address has been cleared, it MUST send this
   message element with the status set to 0.





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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Status    |     Length    |         MAC Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   23 for Duplicate IPv6 Address

   Length:   >= 24

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

   Status:   The status of the duplicate IP address.  The value MUST be
      set to 1 when a duplicate address is detected, and 0 when the
      duplicate address has been cleared.

   Length:  The length of the MAC Address field.

   MAC Address:   The MAC Address of the offending device.

4.6.26.  Idle Timeout

   The Idle Timeout message element is sent by the AC to the WTP to
   provide the idle timeout value that the WTP SHOULD enforce for its
   active stations.  The value applies to all radios on the WTP.

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

   Type:   23 for Idle Timeout

   Length:   4

   Timeout:   The current idle timeout to be enforced by the WTP.  The
      default value for this message element is specified in
      Section 4.8.5.




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4.6.27.  Image Data

   The Image Data message element is present in the Image Data Request
   message sent by the AC and contains the following fields.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Opcode    |                  Value ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   24 for Image Data

   Length:   >= 1

   Opcode:   An 8-bit value representing the transfer opcode.  The
      following values are supported:

      1 -  Image data is included

      2 -  Last Image Data Block is included (EOF)

      5 -  An error occurred.  Transfer is aborted

   Value:   The Image Data field contains up to 1024 characters.  If the
      block being sent is the last one, the Opcode is set to 2.  The AC
      MAY opt to abort the data transfer by setting the Opcode to 5.
      When the Opcode is 5, the Value field has a zero length.

4.6.28.  Image Identifier

   The Image Identifier message element is sent by the AC to the WTP and
   is used to indicate the expected active software version that is to
   be run on the WTP.  The value is a variable length UTF-8 encoded
   string, which is NOT zero terminated.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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   Type:   25 for Image Identifier

   Length:   >= 1

   Value:   A variable length UTF-8 encoded string containing the
      firmware identifier to be run on the WTP.

4.6.29.  Image Information

   The Image Information message element is present in the Image Data
   Response message sent by the AC to the WTP and contains the following
   fields.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           File Size                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              Hash                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              Hash                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              Hash                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              Hash                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   26 for Image Information

   Length:   18

   File Size:   A 32-bit value containing the size of the file, in
      bytes, that will be transferred by the AC to the WTP.

   Hash:   A 16 octet hash of the image.  The hash is computed using
      MD5, using the following pseudo-code:

           #include <md5.h>
           CapwapCreateHash(char *hash, char *image, int image_len)
           {
                   MD_CTX context;

                   MDInit (&context);
                   MDUpdate (&context, buffer, len);
                   MDFinal (hash, &context);
           }





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4.6.30.  Initiate Download

   The Initiate Download message element is used by the AC to inform the
   WTP that the WTP SHOULD initiate a firmware upgrade.  The WTP
   subsequently transmits an Image Data Request message which includes
   the Image Download message element.  This message element does not
   contain any data.

   Type:   27 for Initiate Download

   Length:   0

4.6.31.  Location Data

   The Location Data message element is a variable length byte UTF-8
   encoded string containing user defined location information (e.g.
   "Next to Fridge").  This information is configurable by the network
   administrator, and allows the WTP location to be determined.  The
   string is not zero terminated.

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

   Type:   28 for Location Data

   Length:   > 0

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

4.6.32.  Maximum Message Length

   The Maximum Message Length message element is included in the Join
   Request message by the WTP to indicate the maximum CAPWAP message
   length that it supports to the AC.  The Maximum Message Length
   message element is optionally included in Join Response message by
   the AC to indicate the maximum CAPWAP message length that it supports
   to the WTP.

         0              1               2
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
        |   Maximum Message Length     |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-




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   Type:   29 for Maximum Message Length

   Length:   2

   Maximum Message Length  An 16-bit unsigned integer indicating the
      maximum message length.

4.6.33.  Radio Administrative State

   The Radio Administrative State message element is used to communicate
   the state of a particular radio.  The Radio Administrative State
   message element is sent by the AC to change the state of the WTP.
   The WTP saves the value, to ensure that it remains across WTP resets.
   The WTP communicates this message element during the configuration
   phase, in the Configuration Status Request message, to ensure that AC
   has the WTP radio current administrative state settings.  The message
   element contains the following fields.

         0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID    |  Admin State  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   31 for Radio Administrative State

   Length:   2

   Radio ID:   An 8-bit value representing the radio to configure.  The
      Radio ID field MAY also include the value of 0xff, which is used
      to identify the WTP.  If an AC wishes to change the administrative
      state of a WTP, it includes 0xff in the Radio ID field.

   Admin State:   An 8-bit value representing the administrative state
      of the radio.  The default value for the Admin State field is
      listed in Section 4.8.1.  The following values are supported:

      1 -  Enabled

      2 -  Disabled

4.6.34.  Radio Operational State

   The Radio Operational State message element is sent by the WTP to the
   AC to communicate a radio's operational state.  This message element
   is included in the Configuration Update Response message by the WTP
   if it was requested to change the state of its radio, via the Radio
   Administrative State message element, but was unable to comply to the



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   request.  This message element is included in the Change State Event
   message when a WTP radio state was changed unexpectedly.  This could
   occur due to a hardware failure.  Note that the operational state
   setting is not saved on the WTP, and therefore does not remain across
   WTP resets.  The value contains three fields, as shown below.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID    |     State     |     Cause     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   32 for Radio Operational State

   Length:   3

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

   State:   An 8-bit boolean value representing the state of the radio.
      A value of one disables the radio, while a value of two enables
      it.

   Cause:   When a radio is inoperable, the cause field contains the
      reason the radio is out of service.  The following values are
      supported:

      0 -  Normal

      1 -  Radio Failure

      2 -  Software Failure

      3 -  Administratively Set

4.6.35.  Result Code

   The Result Code message element value is a 32-bit integer value,
   indicating the result of the Request message corresponding to the
   Sequence Number included in the Response message.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Result Code                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Type:   33 for Result Code

   Length:   4

   Result Code:   The following values are defined:

      0  Success

      1  Failure (AC List message element MUST be present)

      2  Success (NAT detected)

      3  Join Failure (unspecified)

      4  Join Failure (Resource Depletion)

      5  Join Failure (Unknown Source)

      6  Join Failure (Incorrect Data)

      7  Join Failure (Session ID already in use)

      8  Join Failure (WTP Hardware not supported)

      9  Join Failure (Binding Not Supported)

      10 Reset Failure (Unable to Reset)

      11 Reset Failure (Firmware Write Error)

      12 Configuration Failure (Unable to Apply Requested Configuration
         - Service Provided Anyhow)

      13 Configuration Failure (Unable to Apply Requested Configuration
         - Service Not Provided)

      14 Image Data Error (Invalid Checksum)

      15 Image Data Error (Invalid Data Length)

      16 Image Data Error (Other Error)

      17 Image Data Error (Image Already Present)

      18 Message Unexpected (Invalid in current state)






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      19 Message Unexpected (Unrecognized Request)

      20 Failure - Missing Mandatory Message Element

      21 Failure - Unrecognized Message Element

4.6.36.  Returned Message Element

   The Returned Message Element is sent by the WTP in the Change State
   Event Request message to communicate to the AC which message elements
   in the Configuration Status Response it was unable to apply locally.
   The Returned Message Element message element contains a result code
   indicating the reason that the configuration could not be applied,
   and encapsulates the failed message element.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Reason     |       Message Element...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   34 for Returned Message Element

   Length:   >= 1

   Reason:   The reason why the configuration in the offending message
      element could not be applied by the WTP.

      1 -  Unknown Message Element

      2 -  Unsupported Message Element

      3 -  Unknown Message Element Value

      4 -  Unsupported Message Element Value

   Message Element:   The Message Element field encapsulates the message
      element sent by the AC in the Configuration Status Response
      message that caused the error.

4.6.37.  Session ID

   The Session ID message element value contains a randomly generated
   unsigned 32-bit integer.







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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Session ID                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   35 for Session ID

   Length:   16

   Session ID:   A 32-bit unsigned integer used as a random session
      identifier

4.6.38.  Statistics Timer

   The Statistics Timer message element value is used by the AC to
   inform the WTP of the frequency with which it expects to receive
   updated statistics.

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

   Type:   36 for Statistics Timer

   Length:   2

   Statistics Timer:   A 16-bit unsigned integer indicating the time, in
      seconds.  The default value for this timer is specified in
      Section 4.7.14.

4.6.39.  Vendor Specific Payload

   The Vendor Specific Payload message element is used to communicate
   vendor specific information between the WTP and the AC.  The Vendor
   Specific Payload message element MAY be present in any CAPWAP
   message.  The message element uses the following format:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Element ID           |   Value...    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   Type:   37 for Vendor Specific

   Length:   >= 7

   Vendor Identifier:   A 32-bit value containing the IANA assigned "SMI
      Network Management Private Enterprise Codes" [18]

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

   Value:   The value associated with the vendor specific element.

4.6.40.  WTP Board Data

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

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=0                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=1                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Optional additional vendor specific WTP board data TLVs.....
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   38 for WTP Board Data

   Length:   >=14

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

   Type:   The following values are supported:

      0 - WTP Model Number:   The WTP Model Number MUST be included in
         the WTP Board Data message element.






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      1 - WTP Serial Number:   The WTP Serial Number MUST be included in
         the WTP Board Data message element.

      2 - Board ID:   A hardware identifier, which MAY be included in
         the WTP Board Data message element.

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

      4 - Base MAC Address   The WTP's Base MAC Address, which MAY be
         assigned to the primary Ethernet interface.

4.6.41.  WTP Descriptor

   The WTP Descriptor message element is used by a WTP to communicate
   its current hardware and software (firmware) configuration.  The
   value contains the following fields.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Max Radios  | Radios in use |    Encryption Capabilities    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=0                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=1                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=2                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Vendor Identifier                       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Type=3                 |             Length           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Value...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   Type:   39 for WTP Descriptor

   Length:   >= 31

   Max Radios:   An 8-bit value representing the number of radios (where
      each radio is identified via the Radio ID field) supported by the
      WTP.

   Radios in use:   An 8-bit value representing the number of radios in
      use in the WTP.

   Encryption Capabilities:   This 16-bit field is used by the WTP to
      communicate its capabilities to the AC.  A WTP that does not have
      any encryption capabilities sets this field to zero (0).  Refer to
      the specific wireless binding for further specification of the
      Encryption Capabilities field.

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

   Type:   The following values are supported.  The Hardware Version,
      Active Software Version, and Boot Version values MUST be included.
      Zero or more Other Software Version values MAY be included.

      0 - Hardware Version:   The WTP hardware version number.

      1 - Active Software Version:   The WTP running software version
         number.

      2 - Boot Version:   The WTP boot loader version number.

      3 - Other Software Version:   The WTP non-running software
         (firmware) version number.

   Length:   Length of vendor specific encoding of WTP information.

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

4.6.42.  WTP Fallback

   The WTP Fallback message element is sent by the AC to the WTP to
   enable or disable automatic CAPWAP fallback in the event that a WTP
   detects its preferred AC, and is not currently connected to it.







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      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |     Mode      |
     +-+-+-+-+-+-+-+-+

   Type:   40 for WTP Fallback

   Length:   1

   Mode:   The 8-bit value indicates the status of automatic CAPWAP
      fallback on the WTP.  When enabled, if the WTP detects that its
      primary AC is available, and that the WTP is not connected to the
      primary AC, the WTP SHOULD automatically disconnect from its
      current AC and reconnect to its primary AC.  If disabled, the WTP
      will only reconnect to its primary AC through manual intervention
      (e.g., through the Reset Request message).  The default value for
      this field is specified in Section 4.8.10.  The following values
      are supported:

      1 -  Enabled

      2 -  Disabled

4.6.43.  WTP Frame Tunnel Mode

   The WTP Frame Tunnel Mode message element allows the WTP to
   communicate the tunneling modes of operation which it supports to the
   AC.  A WTP that advertises support for all types allows the AC to
   select which type will be used, based on its local policy.

      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     | Tunnel Mode   |
     +-+-+-+-+-+-+-+-+

   Type:   41 for WTP Frame Tunnel Mode

   Length:   1

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







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

      2 - 802.3 Frame Tunnel Mode:   The 802.3 Frame Tunnel Mode
         requires the WTP and AC to encapsulate all user payload as
         native IEEE 802.3 frames (see Section 4.4).  All user traffic
         is tunneled to the AC.  This value MUST NOT be used when the
         WTP MAC Type is set to Split-MAC.

      4 - Native Frame Tunnel Mode:   Native Frame Tunnel mode requires
         the WTP and AC to encapsulate all user payloads as native
         wireless frames, as defined by the wireless binding (see for
         example Section 4.4).

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

4.6.44.  WTP IPv4 IP Address

   The WTP IPv4 address is used to perform NAT detection.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      WTP IPv4 IP Address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   42 for WTP IPv4 IP Address

   Length:   4

   WTP IPv4 IP Address:   The IPv4 address from which the WTP is sending
      packets.  This field is used for NAT detection.

4.6.45.  WTP IPv6 IP Address

   The WTP IPv6 address is used to perform NAT detection (e.g., IPv4 to
   IPv6 NAT to help with technology transition).










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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      WTP IPv6 IP Address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      WTP IPv6 IP Address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      WTP IPv6 IP Address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                      WTP IPv6 IP Address                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   43 for WTP IPv6 IP Address

   Length:   32

   WTP IPv6 IP Address:   The IPv6 address from which the WTP is sending
      packets.  This field is used for NAT detection.

4.6.46.  WTP MAC Type

   The WTP MAC-Type message element allows the WTP to communicate its
   mode of operation to the AC.  A WTP that advertises support for both
   modes allows the AC to select the mode to use, based on local policy.

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

   Type:   44 for WTP MAC Type

   Length:   1

   MAC Type:   The MAC mode of operation supported by the WTP.  The
      following values are supported

      0 - Local-MAC:   Local-MAC is the default mode that MUST be
         supported by all WTPs.

      1 - Split-MAC:   Split-MAC support is optional, and allows the AC
         to receive and process native wireless frames.







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

4.6.47.  WTP Name

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

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

   Type:   45 for WTP Name

   Length:   variable

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

4.6.48.  WTP Operational Statistics

   The WTP Operational Statistics message element is sent by the WTP to
   the AC to provide statistics related to the operation of the WTP.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID   | Tx Queue Level | Wireless Link Frames per Sec  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   46 for WTP Operational Statistics

   Length:   4

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

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






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

4.6.49.  WTP Radio Statistics

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

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Radio ID    | Last Fail Type|       Reset Count             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     SW Failure Count          |        HW Failure Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Other  Failure Count       |   Unknown Failure Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Config Update Count         |    Channel Change Count       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Band Change Count           |    Current Noise Floor        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type:   47 for WTP Radio Statistics

   Length:   20

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

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

      0 -  Statistic Not Supported

      1 -  Software Failure

      2 -  Hardware Failure

      3 -  Other Failure

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

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







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

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

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

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

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

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

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

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

4.6.50.  WTP Reboot Statistics

   The WTP Reboot Statistics message element is sent by the WTP to the
   AC to communicate reasons why WTP reboots have occurred.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         Reboot Count          |    AC Initiated Count         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Link Failure Count       |    SW Failure Count           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      HW Failure Count         |    Other Failure Count        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Unknown Failure Count    |Last Failure Type|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type:   48 for WTP Reboot Statistics

   Length:   15






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   Reboot Count:   The number of reboots that have occurred due to a WTP
      crash.  A value of 65535 implies that this information is not
      available on the WTP.

   AC Initiated Count:   The number of reboots that have occurred at the
      request of a CAPWAP protocol message, such as a change in
      configuration that required a reboot or an explicit CAPWAP
      protocol reset request.  A value of 65535 implies that this
      information is not available on the WTP.

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

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

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

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

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

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

      0 -  Not Supported

      1 -  AC Initiated (see Section 9.2)

      2 -  Link Failure

      3 -  Software Failure

      4 -  Hardware Failure

      5 -  Other Failure

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

4.6.51.  WTP Static IP Address Information

   The WTP Static IP Address Information message element is used by an
   AC to configure or clear a previously configured static IP address on
   a WTP.



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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IP Address                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Netmask                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Gateway                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Static     |
     +-+-+-+-+-+-+-+-+

   Type:   49 for WTP Static IP Address Information

   Length:   13

   IP Address:   The IP Address to assign to the WTP.  This field is
      only valid if the static field is set to one.

   Netmask:   The IP Netmask.  This field is only valid if the static
      field is set to one.

   Gateway:   The IP address of the gateway.  This field is only valid
      if the static field is set to one.

   Netmask:   The IP Netmask.  This field is only valid if the static
      field is set to one.

   Static:   An 8-bit boolean stating whether the WTP should use a
      static IP address or not.  A value of zero disables the static IP
      address, while a value of one enables it.

4.7.  CAPWAP Protocol Timers

   This section contains the CAPWAP timers.

4.7.1.  ChangeStatePendingTimer

   The maximum time, in seconds, the AC will wait for the Change State
   Event Request from the WTP after having transmitted a successful
   Configuration Status Response message.  The default value is 25
   seconds.

4.7.2.  DataChannelKeepAlive

   The DataChannelKeepAlive timer is used by the WTP to determine the
   next opportunity when it must transmit the Data Channel KeepAlive.




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   Default: 30

4.7.3.  DataChannelDeadInterval

   The minimum time, in seconds, a WTP MUST wait without having received
   a Data Channel Keep Alive packet before the destination for the Data
   Channel Keep Alive packets may be considered dead.  The value of this
   timer MUST be no less than 2*DataChannelKeepAlive seconds and no
   greater that 240 seconds.

   Default: 5

4.7.4.  DataCheckTimer

   The number of seconds the AC will wait for the Data Channel Keep
   Alive, which is required by the CAPWAP state machine's Data Check
   state.  The AC resets the state machine if this timer expires prior
   to transitioning to the next state.

   Default: 30

4.7.5.  DiscoveryInterval

   The minimum time, in seconds, that a WTP MUST wait after receiving a
   Discovery Response message, before initiating a DTLS handshake.

   Default: 5

4.7.6.  DTLSSessionDelete

   The minimum time, in seconds, a WTP MUST wait for DTLS session
   deletion.

   Default: 5

4.7.7.  EchoInterval

   The minimum time, in seconds, between sending Echo Request messages
   to the AC with which the WTP has joined.

   Default: 30

4.7.8.  ImageDataStartTimer

   The number of seconds the AC will wait for the WTP to initiate the
   Image Data process.

   Default: 30



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4.7.9.  MaxDiscoveryInterval

   The maximum time allowed between sending Discovery Request messages,
   in seconds.  This value MUST be no less than 2 seconds and no greater
   than 180 seconds.

   Default: 20 seconds.

4.7.10.  MaxFailedDTLSSessionRetry

   The maximum number of failed DTLS session establishment attempts
   before the CAPWAP device enters a silent period.

   Default: 3.

4.7.11.  ResponseTimeout

   The minimum time, in seconds, in which the WTP or AC MUST respond to
   a CAPWAP Request message.

   Default: 1

4.7.12.  RetransmitInterval

   The minimum time, in seconds, in which a non-acknowledged CAPWAP
   packet will be retransmitted.

   Default: 3

4.7.13.  SilentInterval

   For a WTP, this is the minimum time, in seconds, a WTP MUST wait
   before it MAY again send Discovery Request messages or attempt to a
   establish DTLS session.  For an AC, this is the minimum time, in
   seconds, during which the AC SHOULD ignore all CAPWAP and DTLS
   packets received from the WTP that is in the Sulking state.

   Default: 30

4.7.14.  StatisticsTimer

   The default Statistics Interval is 120 seconds.

4.7.15.  WaitDTLS

   The maximum time, in seconds, a WTP MUST wait without having received
   a DTLS Handshake message from an AC.  This timer MUST be greater than
   30 seconds.



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   Default: 60

4.7.16.  WaitJoin

   The maximum time, in seconds, after which the DTLS session has been
   established that the AC will wait before receiving a Join Request
   message.  This timer MUST be greater than 30 seconds.

   Default: 60

4.8.  CAPWAP Protocol Variables

   A WTP or AC that implements the CAPWAP Discovery phase MUST allow for
   the following variables to be configured by system management;
   default values are specified, making explicit configuration
   unnecessary in many cases.  If the default values are explicitly
   overridden by the AC, the WTP MUST save the values sent by the AC.

4.8.1.  AdminState

   The default Administrative State value is enabled (1).

4.8.2.  DiscoveryCount

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

4.8.3.  FailedDTLSAuthFailCount

   The number of failed DTLS session establishment attempts due to
   authentication failures.

4.8.4.  FailedDTLSSessionCount

   The number of failed DTLS session establishment attempts.

4.8.5.  IdleTimeout

   The default Idle Timeout is 300 seconds.

4.8.6.  MaxDiscoveries

   The maximum number of Discovery Request messages that will be sent
   after a WTP boots.

   Default: 10





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4.8.7.  MaxRetransmit

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

   Default: 5

4.8.8.  ReportInterval

   The default Report Interval is 120 seconds.

4.8.9.  RetransmitCount

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

4.8.10.  WTPFallBack

   The default WTP Fallback value is enabled (1).

4.9.  WTP Saved Variables

   In addition to the values defined in Section 4.8, the following
   values SHOULD be saved on the WTP in non-volatile memory.  CAPWAP
   wireless bindings MAY define additional values that SHOULD be stored
   on the WTP.

4.9.1.  AdminRebootCount

   The number of times the WTP has rebooted administratively, defined in
   Section 4.6.50.

4.9.2.  FrameEncapType

   For WTPs that support multiple Frame Encapsulation Types, it is
   useful to save the value configured by the AC.  The Frame
   Encapsulation Type is defined in Section 4.6.43.

4.9.3.  LastRebootReason

   The reason why the WTP last rebooted, defined in Section 4.6.50.

4.9.4.  MacType

   For WTPs that support multiple MAC Types, it is useful to save the
   value configured by the AC.  The MACType is defined in
   Section 4.6.46.




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4.9.5.  PreferredACs

   The preferred ACs, with the index, defined in Section 4.6.5.

4.9.6.  RebootCount

   The number of times the WTP has rebooted, defined in Section 4.6.50.

4.9.7.  Static ACL Table

   The static ACL table saved on the WTP, as configured by the Add
   Static MAC ACL Entry message element, see Section 4.6.9.

4.9.8.  Static IP Address

   The static IP Address assigned to the WTP, as configured by the WTP
   Static IP Address Information message element (see Section 4.6.51).

4.9.9.  WTPLinkFailureCount

   The number of times the link to the AC has failed, see
   Section 4.6.50.

4.9.10.  WTPLocation

   The WTP Location, defined in Section 4.6.31.

4.9.11.  WTPName

   The WTP Name, defined in Section 4.6.47.





















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5.  CAPWAP Discovery Operations

   The Discovery messages are used by a WTP to determine which ACs are
   available to provide service, and the capabilities and load of the
   ACs.

5.1.  Discovery Request Message

   The Discovery Request message is used by the WTP to automatically
   discover potential ACs available in the network.  The Discovery
   Request message provides ACs with the primary capabilities of the
   WTP.  A WTP must exchange this information to ensure subsequent
   exchanges with the ACs are consistent with the WTP's functional
   characteristics.

   Discovery Request messages MUST be sent by a WTP in the Discover
   state after waiting for a random delay less than
   MaxDiscoveryInterval, after a WTP first comes up or is
   (re)initialized.  A WTP MUST send no more than the maximum of
   MaxDiscoveries Discovery Request messages, waiting for a random delay
   less than MaxDiscoveryInterval between each successive message.

   This is to prevent an explosion of WTP Discovery Request messages.
   An example of this occurring is when many WTPs are powered on at the
   same time.

   If a Discovery Response message is not received after sending the
   maximum number of Discovery Request messages, the WTP enters the
   Sulking state and MUST wait for an interval equal to SilentInterval
   before sending further Discovery Request messages.

   Upon receiving a Discovery Request message, the AC will respond with
   a Discovery Response message sent to the address in the source
   address of the received Discovery Request message.  Once a Discovery
   Response has been received, if the WTP decides to establish a session
   with the responding AC, it SHOULD perform an MTU discovery, using the
   process described in Section 3.5.

   It is possible for the AC to receive a cleartext Discovery Request
   message while a DTLS session is already active with the WTP.  This is
   most likely the case if the WTP has rebooted, perhaps due to a
   software or power failure, but could also be caused by a DoS attack.
   In such cases, any WTP state, including the state machine instance,
   MUST NOT be cleared until another DTLS session has been successfully
   established, communicated via the DTLSSessionEstablished DTLS
   notification (see Section 2.3.2.2).

   The binding specific WTP Radio Information message element (see



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   Section 2.1) is included in the Discovery Request message to
   advertise WTP support for one or more CAPWAP bindings.

   The Discovery Request message is sent by the WTP when in the
   Discovery State.  The AC does not transmit this message.

   The following message elements MUST be included in the Discovery
   Request message:

   o  Discovery Type, see Section 4.6.23

   o  WTP Board Data, see Section 4.6.40

   o  WTP Descriptor, see Section 4.6.41

   o  WTP Frame Tunnel Mode, see Section 4.6.43

   o  WTP MAC Type, see Section 4.6.46

   o  WTP Radio Information message element(s)that the WTP supports;
      These are defined by the individual link layer CAPWAP Binding
      Protocols (see Section 2.1).

   The following message elements MAY be included in the Discovery
   Request message:

   o  Vendor Specific Payload, see Section 4.6.39

5.2.  Discovery Response Message

   The Discovery Response message provides a mechanism for an AC to
   advertise its services to requesting WTPs.

   When a WTP receives a Discovery Response message, it MUST wait for an
   interval not less than DiscoveryInterval for receipt of additional
   Discovery Response messages.  After the DiscoveryInterval elapses,
   the WTP enters the DTLS-Init state and selects one of the ACs that
   sent a Discovery Response message and send a DTLS Handshake to that
   AC.

   One or more binding specific WTP Radio Information message elements
   (see Section 2.1) are included in the Discovery Request message to
   advertise AC support for the CAPWAP bindings.  The AC MAY include
   only the bindings it shares in common with the WTP, known through the
   WTP Radio Information message elements received in the Discovery
   Request message, or it MAY include all of the bindings supported.
   The WTP MAY use the supported bindings in its AC decision process.
   Note that if the WTP joins an AC that does not support a specific



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   CAPWAP binding, service for that binding MUST NOT be provided by the
   WTP.

   The Discovery Response message is sent by the AC when in the Idle
   State.  The WTP does not transmit this message.

   The following message elements MUST be included in the Discovery
   Response Message:

   o  AC Descriptor, see Section 4.6.1

   o  AC Name, see Section 4.6.4

   o  WTP Radio Information message element(s)that the AC supports;
      These are defined by the individual link layer CAPWAP Binding
      Protocols (see Section 2.1 for more information).

   o  One of the following message elements MUST be included in the
      Discovery Response Message:

      *  CAPWAP Control IPv4 Address, see Section 4.6.10

      *  CAPWAP Control IPv6 Address, see Section 4.6.11

   The following message elements MAY be included in the Discovery
   Response message:

   o  Vendor Specific Payload, see Section 4.6.39

5.3.  Primary Discovery Request Message

   The Primary Discovery Request message is sent by the WTP to determine
   whether its preferred (or primary) AC is available.

   A Primary Discovery Request message is sent by a WTP when it has a
   primary AC configured, and is connected to another AC.  This
   generally occurs as a result of a failover, and is used by the WTP as
   a means to discover when its primary AC becomes available.  Since the
   WTP only has a single instance of the CAPWAP state machine, the
   Primary Discovery Request is sent by the WTP when in the Run State.
   The AC does not transmit this message.

   The frequency of the Primary Discovery Request messages should be no
   more often than the sending of the Echo Request message.

   Upon receipt of a Primary Discovery Request message, the AC responds
   with a Primary Discovery Response message sent to the address in the
   source address of the received Primary Discovery Request message.



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   The following message elements MUST be included in the Primary
   Discovery Request message.

   o  Discovery Type, see Section 4.6.23

   o  WTP Board Data, see Section 4.6.40

   o  WTP Descriptor, see Section 4.6.41

   o  WTP Frame Tunnel Mode, see Section 4.6.43

   o  WTP MAC Type, see Section 4.6.46

   o  WTP Radio Information message element(s)that the WTP supports;
      These are defined by the individual link layer CAPWAP Binding
      Protocols (see Section 2.1 for more information).

   The following message elements MAY be included in the Primary
   Discovery Request message:

   o  Vendor Specific Payload, see Section 4.6.39

5.4.  Primary Discovery Response

   The Primary Discovery Response message enables an AC to advertise its
   availability and services to requesting WTPs that are configured to
   have the AC as its primary AC.

   The Primary Discovery Response message is sent by an AC after
   receiving a Primary Discovery Request message.

   When a WTP receives a Primary Discovery Response message, it may
   establish a CAPWAP protocol connection to its primary AC, based on
   the configuration of the WTP Fallback Status message element on the
   WTP.

   The Primary Discovery Response message is sent by the AC when in the
   Idle State.  The WTP does not transmit this message.

   The following message elements MUST be included in the Primary
   Discovery Response message.

   o  AC Descriptor, see Section 4.6.1

   o  AC Name, see Section 4.6.4

   o  WTP Radio Information message element(s)that the AC supports;
      These are defined by the individual link layer CAPWAP Binding



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      Protocols (see Section 2.1 for more information).

   One of the following message elements MUST be included in the
   Discovery Response Message:

   o  CAPWAP Control IPv4 Address, see Section 4.6.10

   o  CAPWAP Control IPv6 Address, see Section 4.6.11

   The following message elements MAY be included in the Primary
   Discovery Response message:

   o  Vendor Specific Payload, see Section 4.6.39






































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6.  CAPWAP Join Operations

   The Join Request message is used by a WTP to request service from an
   AC after a DTLS connection is established to that AC.  The Join
   Response message is used by the AC to indicate that it will or will
   not provide service.

6.1.  Join Request

   The Join Request message is used by a WTP to request service through
   the AC.  A Join Request message is sent by a WTP after (optionally)
   receiving one or more Discovery Response messages, and completion of
   DTLS session establishment.  When an AC receives a Join Request
   message it responds with a Join Response message.

   Upon completion of the DTLS handshake, and receiving the
   DTLSEstablished notification, the WTP sends the Join Request message
   to the AC.  When the AC is notified of the DTLS session
   establishment, it does not clear the WaitDTLS timer until it has
   received the Join Request message, at which time it sends a Join
   Response message to the WTP, indicating success or failure.

   One or more WTP Radio Information message elements (see Section 2.1)
   are included in the Join Request to request service for the CAPWAP
   bindings by the AC.  Including a binding that is unsupported by the
   AC will result in a failed Join Response.

   If the AC rejects the Join Request, it sends a Join Response message
   with a failure indication and initiates an abort of the DTLS session
   via the DTLSAbort command.

   If an invalid (i.e. malformed) Join Request message is received, the
   message MUST be silently discarded by the AC.  No response is sent to
   the WTP.  The AC SHOULD log this event.

   The Join Request is sent by the WTP when in the Join State.  The AC
   does not transmit this message.

   The following message elements MUST be included in the Join Request
   message.

   o  Location Data, see Section 4.6.31

   o  WTP Board Data, see Section 4.6.40

   o  WTP Descriptor, see Section 4.6.41





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   o  WTP Name, see Section 4.6.47

   o  Session ID, see Section 4.6.37

   o  WTP Frame Tunnel Mode, see Section 4.6.43

   o  WTP MAC Type, see Section 4.6.46

   o  WTP Radio Information message element(s)that the WTP supports;
      These are defined by the individual link layer CAPWAP Binding
      Protocols (see Section 2.1 for more information).

   At least one of the following message element MUST be included in the
   Join Request message.

   o  WTP IPv4 IP Address, see Section 4.6.44

   o  WTP IPv6 IP Address, see Section 4.6.45

   The following message element MAY be included in the Join Request
   message.

   o  Maximum Message Length, see Section 4.6.32

   o  WTP Reboot Statistics, see Section 4.6.50

   o  WTP IPv4 IP Address, see Section 4.6.44

   o  WTP IPv6 IP Address, see Section 4.6.45

   o  Vendor Specific Payload, see Section 4.6.39

6.2.  Join Response

   The Join Response message is sent by the AC to indicate to a WTP that
   it is capable and willing to provide service to the WTP.

   The WTP, receiving a Join Response message, checks for success or
   failure.  If the message indicates success, the WTP clears the
   WaitDTLS timer for the session and proceeds to the Configure state.

   If the WaitDTLS Timer expires prior to reception of the Join Response
   message, the WTP MUST terminate the handshake, deallocate session
   state and initiate the DTLSAbort command.

   If an invalid (malformed) Join Response message is received, the WTP
   SHOULD log an informative message detailing the error.  This error
   MUST be treated in the same manner as AC non-responsiveness.  The



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   WaitDTLS timer will eventually expire, and the WTP MAY (if it is so
   configured) attempts to join a new AC.

   If one of the WTP Radio Information message elements (see
   Section 2.1) in the Join Request message requested support for a
   CAPWAP binding which the AC does not support, the AC sets the Result
   Code message element to "Binding Not Supported".

   The AC includes the Image Identifier message element to indicate the
   software version it expects the WTP to run.  This information is used
   to determine whether the WTP MUST either change its currently running
   firmware image, or download a new version (see Section 9.1.1).

   The Join Response message is sent by the AC when in the Join State.
   The WTP does not transmit this message.

   The following message elements MAY be included in the Join Response
   message.

   o  AC IPv4 List, see Section 4.6.2

   o  AC IPv6 List, see Section 4.6.3

   o  Image Identifier, see Section 4.6.28

   o  Maximum Message Length, see Section 4.6.32

   o  Vendor Specific Payload, see Section 4.6.39

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

   o  Result Code, see Section 4.6.35

   o  AC Descriptor, see Section 4.6.1

   o  AC Name, see Section 4.6.4

   o  WTP Radio Information message element(s)that the AC supports;
      These are defined by the individual link layer CAPWAP Binding
      Protocols (see Section 2.1).

   One of the following message elements MUST be included in the
   Discovery Response Message:

   o  CAPWAP Control IPv4 Address, see Section 4.6.10





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   o  CAPWAP Control IPv6 Address, see Section 4.6.11


















































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7.  Control Channel Management

   The Control Channel Management messages are used by the WTP and AC to
   maintain a control communication channel.  CAPWAP control messages,
   such as the WTP Event Request message sent from the WTP to the AC
   indicate to the AC that the WTP is operational.  When such control
   messages are not being sent, the Echo Request and Echo Response
   messages are used to maintain the control communication channel.

7.1.  Echo Request

   The Echo Request message is a keep-alive mechanism for CAPWAP control
   messages.

   Echo Request messages are sent periodically by a WTP in the Run state
   (see Section 2.3) to determine the state of the control connection
   between the WTP and the AC.  The Echo Request message is sent by the
   WTP when the EchoInterval timer expires.

   The Echo Request message is sent by the WTP when in the Run State.
   The AC does not transmit this message.

   The following message elements MAY be included in the Echo Request
   message:

   o  Vendor Specific Payload, see Section 4.6.39

   When an AC receives an Echo Request message it responds with an Echo
   Response message.

7.2.  Echo Response

   The Echo Response message acknowledges the Echo Request message.

   An Echo Response message is sent by an AC after receiving an Echo
   Request message.  After transmitting the Echo Response message, the
   AC SHOULD reset its EchoInterval timer.  If another Echo Request
   message or other control message is not received by the AC when the
   timer expires, the AC SHOULD consider the WTP to be no longer
   reachable.

   The Echo Response message is sent by the AC when in the Run State.
   The WTP does not transmit this message.

   The following message elements MAY be included in the Echo Response
   message:





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   o  Vendor Specific Payload, see Section 4.6.39

   When a WTP receives an Echo Response message it initializes the
   EchoInterval to the configured value.















































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8.  WTP Configuration Management

   WTP Configuration messages are used to exchange configuration
   information between the AC and the WTP.

8.1.  Configuration Consistency

   The CAPWAP protocol provides flexibility in how WTP configuration is
   managed.  A WTP has two options:

   1. The WTP retains no configuration and accepts the configuration
      provided by the AC.

   2. The WTP retains the configuration of parameters provided by the AC
      that are non-default values.

   If the WTP opts to save configuration locally, the CAPWAP protocol
   state machine defines the Configure state, which allows for
   configuration exchange.  In the Configure state, the WTP sends its
   current configuration overrides to the AC via the Configuration
   Status message.  A configuration override is a non-default parameter.
   As an example, in the CAPWAP protocol, the default antenna
   configuration is internal omni antenna.  A WTP that either has no
   internal antennas, or has been explicitly configured by the AC to use
   external antennas, sends its antenna configuration during the
   configure phase, allowing the AC to become aware of the WTP's current
   configuration.

   Once the WTP has provided its configuration to the AC, the AC sends
   its configuration to the WTP.  This allows the WTP to receive
   configuration and policies from the AC.

   The AC maintains a copy of each active WTP configuration.  There is
   no need for versioning or other means to identify configuration
   changes.  If a WTP becomes inactive, the AC MAY delete the inactive
   WTP configuration.  If a WTP fails, and connects to a new AC, the WTP
   provides its overridden configuration parameters, allowing the new AC
   to be aware of the WTP configuration.

   This model allows for resiliency in case of an AC failure, ensuring
   another AC can provide service to the WTP.  A new AC would be
   automatically updated with WTP configuration changes, eliminating the
   need for inter-AC communication and the need for all ACs to be aware
   of the configuration of all WTPs in the network.

   Once the CAPWAP protocol enters the Run state, the WTPs begin to
   provide service.  It is common for administrators to require that
   configuration changes be made while the network is operational.



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   Therefore, the Configuration Update Request is sent by the AC to the
   WTP to make these changes at run-time.

8.1.1.  Configuration Flexibility

   The CAPWAP protocol provides the flexibility to configure and manage
   WTPs of varying design and functional characteristics.  When a WTP
   first discovers an AC, it provides primary functional information
   relating to its type of MAC and to the nature of frames to be
   exchanged.  The AC configures the WTP appropriately.  The AC also
   establishes corresponding internal state for the WTP.

8.2.  Configuration Status

   The Configuration Status message is sent by a WTP to deliver its
   current configuration to the AC.

   The Configuration Status message carries binding specific message
   elements.  Refer to the appropriate binding for the definition of
   this structure.

   When an AC receives a Configuration Status message it acts upon the
   content of the message and responds to the WTP with a Configuration
   Status Response message.

   The Configuration Status message includes multiple Radio
   Administrative State message elements, one for the WTP, and one for
   each radio in the WTP.

   The Configuration Status message is sent by the WTP when in the
   Configure State.  The AC does not transmit this message.

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

   o  AC Name, see Section 4.6.4

   o  AC Name with Index, see Section 4.6.5

   o  Radio Administrative State, see Section 4.6.33

   o  Statistics Timer, see Section 4.6.38

   o  WTP Reboot Statistics, see Section 4.6.50

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




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   o  WTP Static IP Address Information, see Section 4.6.51

   o  Vendor Specific Payload, see Section 4.6.39

8.3.  Configuration Status Response

   The Configuration Status Response message is sent by an AC and
   provides a mechanism for the AC to override a WTP's requested
   configuration.

   A Configuration Status Response message is sent by an AC after
   receiving a Configuration Request message.

   The Configuration Status Response message carries binding specific
   message elements.  Refer to the appropriate binding for the
   definition of this structure.

   When a WTP receives a Configuration Status Response message it acts
   upon the content of the message, as appropriate.  If the
   Configuration Status Response message includes a Radio Operational
   State message element that causes a change in the operational state
   of one of the radios, the WTP transmits a Change State Event to the
   AC, as an acknowledgement of the change in state.

   The Configuration Status Response message is sent by the AC when in
   the Configure State.  The WTP does not transmit this message.

   The following message elements MUST be included in the Configuration
   Status Response message.

   o  AC IPv4 List, see Section 4.6.2

   o  AC IPv6 List, see Section 4.6.3

   o  CAPWAP Timers, see Section 4.6.14

   o  Decryption Error Report Period, see Section 4.6.19

   o  Idle Timeout, see Section 4.6.26

   o  WTP Fallback, see Section 4.6.42

   The following message element MAY be included in the Configuration
   Status Response message.

   o  WTP Static IP Address Information, see Section 4.6.51





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   o  Vendor Specific Payload, see Section 4.6.39

8.4.  Configuration Update Request

   Configuration Update Request messages are sent by the AC to provision
   the WTP while in the Run state.  This is used to modify the
   configuration of the WTP while it is operational.

   When a WTP receives a Configuration Update Request message, it
   responds with a Configuration Update Response message, with a Result
   Code message element indicating the result of the configuration
   request.

   The AC includes the Image Identifier and Initiate Download message
   elements to force the WTP to update its firmware while in the Run
   state.  The WTP MAY proceed to download the requested firmware if it
   determines the version specified in the Image Identifier message
   element is not in its non-volatile storage (see Section 9.1.1).

   The Configuration Update Request is sent by the AC when in the Run
   State.  The WTP does not transmit this message.

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

   o  AC Name with Index, see Section 4.6.5

   o  AC Timestamp, see Section 4.6.6

   o  Add MAC ACL Entry, see Section 4.6.7

   o  Add Static MAC ACL Entry, see Section 4.6.9

   o  CAPWAP Timers, see Section 4.6.14

   o  Decryption Error Report Period, see Section 4.6.19

   o  Delete MAC ACL Entry, see Section 4.6.20

   o  Delete Static MAC ACL Entry, see Section 4.6.22

   o  Idle Timeout, see Section 4.6.26

   o  Location Data, see Section 4.6.31

   o  Radio Administrative State, see Section 4.6.33





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   o  Statistics Timer, see Section 4.6.38

   o  WTP Fallback, see Section 4.6.42

   o  WTP Name, see Section 4.6.47

   o  WTP Static IP Address Information, see Section 4.6.51

   o  Image Identifier, see Section 4.6.28

   o  Initiate Download, see Section 4.6.30

   o  Vendor Specific Payload, see Section 4.6.39

8.5.  Configuration Update Response

   The Configuration Update Response message is the acknowledgement
   message for the Configuration Update Request message.

   The Configuration Update Response message is sent by a WTP after
   receiving a Configuration Update Request message.

   When an AC receives a Configuration Update Response message the
   result code indicates if the WTP successfully accepted the
   configuration.

   The Configuration Update Response message is sent by the WTP when in
   the Run State.  The AC does not transmit this message.

   The following message element MUST be present in the Configuration
   Update message.

   Result Code, see Section 4.6.35

   The following message elements MAY be present in the Configuration
   Update Response message.

   o  Radio Operational State, see Section 4.6.34

   o  Vendor Specific Payload, see Section 4.6.39

8.6.  Change State Event Request

   The Change State Event Request message is used by the WTP for two
   main purposes:

   o  When sent by the WTP following the reception of a Configuration
      Status Response message from the AC, the WTP uses the Change State



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      Event Request message to provide an update on the WTP radio's
      operational state and to confirm that the configuration provided
      by the AC was successfully applied.

   o  When sent during the Run state, the WTP uses the Change State
      Event Request message to notify the AC of an unexpected change in
      the WTP's radio operational state.

   When an AC receives a Change State Event Request message it responds
   with a Change State Event Response message and modifies its data
   structures for the WTP as needed.  The AC MAY decide not to provide
   service to the WTP if it receives an error, based on local policy,
   and to transition to the Reset state.

   The Change State Event Request message is sent by a WTP to
   acknowledge or report an error condition to the AC for a requested
   configuration in the Configuration Status Response message.  The
   Change State Event Request message includes the Result Code message
   element, which indicates whether the configuration was successfully
   applied.  If the WTP is unable to apply a specific configuration
   request, it indicates the failure by including one or more Returned
   Message Element message elements (see Section 4.6.36).

   The Change State Event Request message is sent by the WTP in the
   Configure or Run State.  The AC does not transmit this message.

   The WTP MAY save its configuration to persistent storage prior to
   transmitting the response.  However, this is implementation specific
   and is not required.

   The following message elements MUST be present in the Change State
   Event Request message.

   o  Radio Operational State, see Section 4.6.34

   o  Result Code, see Section 4.6.35

   One or more of the following message elements MAY be present in the
   Change State Event Request message.

   o  Returned Message Element(s), see Section 4.6.36

   o  Vendor Specific Payload, see Section 4.6.39








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8.7.  Change State Event Response

   The Change State Event Response message acknowledges the Change State
   Event Request message.

   A Change State Event Response message is sent by an AC in response to
   a Change State Event Request message.

   The Change State Event Response message is sent by the AC when in the
   Configure or Run state.  The WTP does not transmit this message.

   The following message elements MAY be included in the Change State
   Event Response message:

   o  Vendor Specific Payload, see Section 4.6.39

   The WTP does not take any action upon receipt of the Change State
   Event Response message.

8.8.  Clear Configuration Request

   The Clear Configuration Request message is used to reset the WTP
   configuration.

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

   The Clear Configuration Request is sent by the AC when in the Run
   State.  The WTP does not transmit this message.

   The following message elements MAY be included in the Clear
   Configuration Request message:

   o  Vendor Specific Payload, see Section 4.6.39

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

8.9.  Clear Configuration Response

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

   The Clear Configuration Response is sent by the WTP when in the Run
   State.  The AC does not transmit this message.



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   The Clear Configuration Request message MUST include the following
   message element.

   o  Result Code, see Section 4.6.35

   The following message elements MAY be included in the Clear
   Configuration Request message:

   o  Vendor Specific Payload, see Section 4.6.39










































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9.  Device Management Operations

   This section defines CAPWAP operations responsible for debugging,
   gathering statistics, logging, and firmware management.

9.1.  Firmware Management

   This section describes the firmware download procedures used by the
   CAPWAP protocol.  Firmware download can occur during the Image Data
   or Run state.

   Figure 4 provides an example of a WTP that performs a firmware
   upgrade while in the Image Data state.  In this example, the WTP does
   not already have the requested firmware (Image Identifier = x), and
   downloads the image from the AC.

             WTP                                               AC

                                Join Request
         -------------------------------------------------------->

                     Join Response (Image Identifier = x)
         <------------------------------------------------------

              Image Data Request (Image Identifier = x)
         -------------------------------------------------------->

           Image Data Response (Result Code = Success,
                                Image Information = {size,hash},
                                Initiate Download)
         <------------------------------------------------------

                Image Data Request (Image Data = Data)
         <------------------------------------------------------

                Image Data Response (Result Code = Success)
         -------------------------------------------------------->

                                  .....

                Image Data Request (Image Data = EOF)
         <------------------------------------------------------

                Image Data Response (Result Code = Success)
         -------------------------------------------------------->

                     (WTP enters the Reset State)




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                  Figure 4: WTP Firmware Download Case 1

   Figure 5 provides an example in which the WTP has the image specified
   by the AC in its non-volative storage.  The WTP opts to NOT download
   the firmware and immediately reset.

             WTP                                               AC

                                Join Request
         -------------------------------------------------------->

                     Join Response (Image Identifier = x)
         <------------------------------------------------------

                     (WTP enters the Reset State)

                  Figure 5: WTP Firmware Download Case 2

   Figure 6 provides an example of a WTP that performs a firmware
   upgrade while in the Run state.  This mode of firmware upgrade allows
   the WTP to download its image while continuing to provide service.
   The WTP will not automatically reset until it is notified by the AC,
   with a Reset Request message.




























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             WTP                                               AC

                Configuration Update Request (Image Identifier = x)
         <------------------------------------------------------

            Configuration Update Response (Result Code = Success)
         -------------------------------------------------------->


              Image Data Request (Image Identifier = x)
         -------------------------------------------------------->

              Image Data Response (Result Code = Success,
                                   Image Information = {size,hash},
                                   Initiate Download)
         <------------------------------------------------------

                Image Data Request (Image Data = Data)
         <------------------------------------------------------

                Image Data Response (Result Code = Success)
         -------------------------------------------------------->

                                  .....

                Image Data Request (Image Data = EOF)
         <------------------------------------------------------

                Image Data Response (Result Code = Success)
         -------------------------------------------------------->

                                  .....

                (administratively requested reboot request)
                   Reset Request (Image Identifier = x)
         <------------------------------------------------------

                  Reset Response (Result Code = Success)
         -------------------------------------------------------->

                  Figure 6: WTP Firmware Download Case 3

   Figure 7 provides another example of the firmware download while in
   the Run state.  In this example, the WTP already has the image
   specified by the AC in its non-volative storage.  The WTP opts to NOT
   download the firmware.  The WTP resets upon receipt of a Reset
   Request message from the AC.




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          WTP                                               AC

          Configuration Update Request (Image Identifier = x,
                                        Image Information = {size,hash},
                                        Initiate Download)
      <------------------------------------------------------

   Configuration Update Response (Result Code = Already Have Image)
      -------------------------------------------------------->

                               .....

             (administratively requested reboot request)
                Reset Request (Image Identifier = x)
      <------------------------------------------------------

               Reset Response (Result Code = Success)
      -------------------------------------------------------->

                  Figure 7: WTP Firmware Download Case 4

9.1.1.  Image Data Request

   The Image Data Request message is used to update firmware on the WTP.
   This message and its companion Response message are used by the AC to
   ensure that the image being run on each WTP is appropriate.

   Image Data Request messages are exchanged between the WTP and the AC
   to download a new firmware image to the WTP.  When a WTP or AC
   receives an Image Data Request message it responds with an Image Data
   Response message.  The message elements contained within the Image
   Data Request message are required to determine the intent of the
   request.

   The decision that new firmware is to be downloaded to the WTP can
   occur in one of two ways:

      When the WTP joins the AC, the Join Response message includes the
      Image Identifier message element, which informs the WTP of the
      firmware it is expected to run. if the WTP does not currently have
      the requested firmware version, it transmits an Image Data Request
      message, with the appropriate Image Identifier message element.
      If the WTP already has the requested firmware, it simply resets.

      Once the WTP is in the Run state, it is possible for the AC to
      cause the WTP to initiate a firmware download by sending a
      Configuration Update Request message with the Initiate Download
      and Image Identifier message elements.  The WTP then transmits the



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      Image Data Request message, which includes the Image Identifier
      message element to start the download process.  Note that when the
      firmware is downloaded in this way, the WTP does not automatically
      reset after the download is complete.  The WTP will only reset
      when it receives a Reset Request message from the AC.  If the WTP
      already had the requested firmware version in its non-volatile
      storage, the WTP does not transmit the Image Data Request message
      and responds with a Configuration Update Response message with the
      Result Code set to Image Already Present.

   Regardless of how the download was initiated, once the AC receives an
   Image Data Request message with the Image Identifier message element,
   it begins the transfer process by transmitting an Image Data Request
   message that includes the Image Data message element.  This continues
   until the firmware image has been transferred.

   The Image Data Request message is sent by the WTP or the AC when in
   the Image Data or Run State.

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

   o  Image Data, see Section 4.6.27

   o  Image Identifier, see Section 4.6.28

   o  Vendor Specific Payload, see Section 4.6.39

9.1.2.  Image Data Response

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

   An Image Data Response message is sent in response to a received
   Image Data Request message.  Its purpose is to acknowledge the
   receipt of the Image Data Request message.  The Result Code is
   included to indicate whether a previously sent Image Data Request
   message was invalid.

   The Image Data Response message is sent by the WTP or the AC when in
   the Image Data or Run State.

   The following message element MUST be included in the Image Data
   Response message.

   o  Result Code, see Section 4.6.35

   The following message elements MAY be included in the Image Data



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   Response message.

   o  Image Information, see Section 4.6.29

   o  Initiate Download, see Section 4.6.30

   o  Vendor Specific Payload, see Section 4.6.39

   Upon receiving an Image Data Response message indicating an error,
   the WTP MAY retransmit a previous Image Data Request message, or
   abandon the firmware download to the WTP by transitioning to the
   Reset state.

9.2.  Reset Request

   The Reset Request message is used to cause a WTP to reboot.

   A Reset Request message is sent by an AC to cause a WTP to
   reinitialize its operation.

   The Reset Request is sent by the AC when in the Run State.  The WTP
   does not transmit this message.

   The following message elements MUST be included in the Reset Request
   message.

   o  Image Identifier, see Section 4.6.28

   The following message elements MAY be included in the Reset Request
   message:

   o  Vendor Specific Payload, see Section 4.6.39

   When a WTP receives a Reset Request message, it responds with a Reset
   Response message indicating success and then reinitialize itself.  If
   the WTP is unable to write to its non-volatile storage, to ensure
   that it runs the requested software version indicated in the Image
   Identifier message element, it MAY send the appropriate Result Code
   message element, but MUST reboot.  If the WTP is unable to reset,
   including a hardware reset, it sends a Reset Response message to the
   AC with a Result Code message element indicating failure.  The AC no
   longer provides service to the WTP.

9.3.  Reset Response

   The Reset Response message acknowledges the Reset Request message.

   A Reset Response message is sent by the WTP after receiving a Reset



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   Request message.

   The Reset Response is sent by the WTP when in the Run State.  The AC
   does not transmit this message.

   The following message element MAY be included in the Reset Response
   message.

   o  Result Code, see Section 4.6.35

   o  Vendor Specific Payload, see Section 4.6.39

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

9.4.  WTP Event Request

   The WTP Event Request message is used by a WTP to send information to
   its AC.  The WTP Event Request message MAY be sent periodically, or
   sent in response to an asynchronous event on the WTP.  For example, a
   WTP MAY collect statistics and use the WTP Event Request message to
   transmit the statistics to the AC.

   When an AC receives a WTP Event Request message it will respond with
   a WTP Event Response message.

   The presence of the Delete Station message element is used by the WTP
   to inform the AC that it is no longer providing service to the
   station.  This could be the result of an Idle Timeout (see
   Section 4.6.26), due to resource shortages, or some other reason.

   The WTP Event Request message is sent by the WTP when in the Run
   State.  The AC does not transmit this message.

   The WTP Event Request message MUST contain one of the message
   elements listed below, or a message element that is defined for a
   specific wireless technology.  More than one of each message element
   listed MAY be included in the WTP Event Request message.

   o  Decryption Error Report, see Section 4.6.18

   o  Duplicate IPv4 Address, see Section 4.6.24

   o  Duplicate IPv6 Address, see Section 4.6.25





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   o  WTP Operational Statistics, see Section 4.6.48

   o  WTP Radio Statistics, see Section 4.6.49

   o  WTP Reboot Statistics, see Section 4.6.50

   o  Delete Station, see Section 4.6.21

   o  Vendor Specific Payload, see Section 4.6.39

9.5.  WTP Event Response

   The WTP Event Response message acknowledges receipt of the WTP Event
   Request message.

   A WTP Event Response message is sent by an AC after receiving a WTP
   Event Request message.

   The WTP Event Response message is sent by the AC when in the Run
   State.  The WTP does not transmit this message.

   The following message elements MAY be included in the WTP Event
   Response message:

   o  Vendor Specific Payload, see Section 4.6.39

9.6.  Data Transfer Request

   The Data Transfer Request message is used to deliver debug
   information from the WTP to the AC.

   Data Transfer Request messages are sent by the WTP to the AC when the
   WTP determines that it has important information to send to the AC.
   For instance, if the WTP detects that its previous reboot was caused
   by a system crash, it can send the crash file to the AC.  The remote
   debugger function in the WTP also uses the Data Transfer Request
   message to send console output to the AC for debugging purposes.

   When the AC receives a Data Transfer Request message it responds to
   the WTP with a Data Transfer Response message.  The AC MAY log the
   information received.

   The Data Transfer Request message is sent by the WTP when in the Run
   State.  The AC does not transmit this message.

   The Data Transfer Request message MUST contain one of the message
   elements listed below.




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   o  Data Transfer Data, see Section 4.6.16

   o  Data Transfer Mode, see Section 4.6.17

   The following message elements MAY be included in the Data Transfer
   Request message:

   o  Vendor Specific Payload, see Section 4.6.39

9.7.  Data Transfer Response

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

   A Data Transfer Response message is sent in response to a received
   Data Transfer Request message.  Its purpose is to acknowledge receipt
   of the Data Transfer Request message.

   The Data Transfer Response message is sent by the AC when in the Run
   State.  The WTP does not transmit this message.

   The following message elements MAY be included in the Data Transfer
   Response message:

   o  Vendor Specific Payload, see Section 4.6.39

   Upon receipt of a Data Transfer Response message, the WTP transmits
   more information, if more information is available.























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10.  Station Session Management

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

10.1.  Station Configuration Request

   The Station Configuration Request message is used to create, modify
   or delete station session state on a WTP.  The message is sent by the
   AC to the WTP, and MAY contain one or more message elements.  The
   message elements for this CAPWAP control message include information
   that is generally highly technology specific.  Refer to the
   appropriate binding document for definitions of the messages elements
   that are included in this control message.

   The Station Configuration Request message is sent by the AC when in
   the Run State.  The WTP does not transmit this message.

   The following CAPWAP Control message elements MAY be included in the
   Station Configuration Request message.  More than one of each message
   element listed MAY be included in the Station Configuration Request
   message.

   o  Add Station, see Section 4.6.8

   o  Delete Station, see Section 4.6.21

   o  Vendor Specific Payload, see Section 4.6.39

10.2.  Station Configuration Response

   The Station Configuration Response message is used to acknowledge a
   previously received Station Configuration Request message.

   The Station Configuration Response message is sent by the WTP when in
   the Run State.  The AC does not transmit this message.

   The following message element MUST be present in the Station
   Configuration Response message.

   o  Result Code, see Section 4.6.35

   The following message elements MAY be included in the Station
   Configuration Response message:

   o  Vendor Specific Payload, see Section 4.6.39

   The Result Code message element indicates that the requested



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   configuration was successfully applied, or that an error related to
   processing of the Station Configuration Request message occurred on
   the WTP.
















































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11.  NAT Considerations

   There are three specific situations in which a NAT deployment may be
   used in conjunction with a CAPWAP-enabled deployment.  The first
   consists of a configuration in which a single WTP is behind a NAT
   system.  Since all communication is initiated by the WTP, and all
   communication is performed over IP using two UDP ports, the protocol
   easily traverses NAT systems in this configuration.

   In the second case, two or more WTPs are deployed behind the same NAT
   system.  Here, the AC would receive multiple connection requests from
   the same IP address, and cannot differentiate the originating WTP of
   the connection requests.  The CAPWAP Data Check state, which
   establishes the data plane connection and communicates the Data
   Keepalive, includes the Session Identifier message element, which is
   used to bind the control and data plane.  Use of the Session
   Identifier message element enables the AC to match the control and
   data plane flows from multiple WTPs behind the same NAT system
   (multiple WTPs sharing the same IP address).

   In the third configuration, the AC is deployed behind a NAT.  Two
   issues exist in this situation.  First, an AC communicates its
   interfaces and corresponding WTP load using the CAPWAP Control IPv4
   Address and CAPWAP Control IPv6 Address message elements.  This
   message element is mandatory, but contains invalid information if a
   middlebox is present between the AC and WTP.  The WTP MUST NOT
   utilize the information in these message elements if it detects a NAT
   (as described in the CAPWAP Transport Protocol message element).
   Note this would disable the load balancing capabilities of the CAPWAP
   protocol.  Alternatively, the AC could have a configured NAT'ed
   address, which it would include in either of the two control address
   message elements.

   The CAPWAP protocol allows for all of the AC identities supporting a
   group of WTPs to be communicated through the AC List message element.
   This feature MUST be ignored by the WTP when it detects the AC is
   behind a middlebox.

   The CAPWAP protocol allows an AC to configure a static IP address on
   a WTP using the WTP Static IP Address Information message element.
   This message element SHOULD NOT be used in NAT'ed environments,
   unless the administrator is familiar with the internal IP addressing
   scheme within the WTP's private network, and does not rely on the
   public address seen by the AC.

   When a WTP detects the duplicate address condition, it generates a
   message to the AC, which includes the Duplicate IP Address message
   element.  The IP Address embedded within this message element is



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   different from the public IP address seen by the AC.


















































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12.  Security Considerations

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

12.1.  CAPWAP Security

   As it is currently specified, the CAPWAP protocol sits between the
   security mechanisms specified by the wireless link layer protocol
   (e.g.IEEE 802.11i) and AAA.  One goal of CAPWAP is to bootstrap trust
   between the STA and WTP using a series of preestablished trust
   relationships:


         STA            WTP           AC            AAA
         ==============================================

                            DTLS Cred     AAA Cred
                         <------------><------------->

                         EAP Credential
          <------------------------------------------>

           wireless link layer
           (e.g.802.11 PTK)
          <--------------> or
          <--------------------------->
              (derived)

   Within CAPWAP, DTLS is used to secure the link between the WTP and
   AC.  In addition to securing control messages, it's also a link in
   this chain of trust for establishing link layer keys.  Consequently,
   much rests on the security of DTLS.

   In some CAPWAP deployment scenarios, there are two channels between
   the WTP and AC: the control channel, carrying CAPWAP control
   messages, and the data channel, over which client data packets are
   tunneled between the AC and WTP.  Typically, the control channel is
   secured by DTLS, while the data channel is not.

   The use of parallel protected and unprotected channels deserves
   special consideration, but does not create a threat.  There are two
   potential concerns: attempting to convert protected data into un-
   protected data and attempting to convert un-protected data into
   protected data.  These concerns are addressed below.





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12.1.1.  Converting Protected Data into Unprotected Data

   Since CAPWAP does not support authentication-only ciphers (i.e. all
   supported ciphersuites include encryption and authentication), it is
   not possible to convert protected data into unprotected data.  Since
   encrypted data is (ideally) indistinguishable from random data, the
   probability of an encrypted packet passing for a well-formed packet
   is effectively zero.

12.1.2.  Converting Unprotected Data into Protected Data (Insertion)

   The use of message authentication makes it impossible for the
   attacker to forge protected records.  This makes conversion of
   unprotected records to protected records impossible.

12.1.3.  Deletion of Protected Records

   An attacker could remove protected records from the stream, though
   not undetectably so, due the built-in reliability of the underlying
   CAPWAP protocol.  In the worst case, the attacker would remove the
   same record repeatedly, resulting in a CAPWAP session timeout and
   restart.  This is effectively a DoS attack, and could be accomplished
   by a man in the middle regardless of the CAPWAP protocol security
   mechanisms chosen.

12.1.4.   Insertion of Unprotected Records

   An attacker could inject packets into the unprotected channel, but
   this may become evident if sequence number desynchronization occurs
   as a result.  Only if the attacker is a MiM can packets be inserted
   undetectably.  This is a consequence of that channel's lack of
   protection, and not a new threat resulting from the CAPWAP security
   mechanism.

12.2.  Session ID Security

   Since DTLS does not export a unique session identifier, there can be
   no explicit protocol binding between the DTLS layer and CAPWAP layer.
   As a result, implementations MUST provide a mechanism for performing
   this binding.  For example, an AC MUST NOT associate decrypted DTLS
   control packets with a particular WTP session based solely on the
   Session ID in the packet header.  Instead, identification should be
   done based on which DTLS session decrypted the packet.  Otherwise one
   authenticated WTP could spoof another authenticated WTP by altering
   the Session ID in the encrypted CAPWAP header.

   It should be noted that when the CAPWAP data channel is unencrypted,
   the WTP Session ID is exposed and possibly known to adversaries and



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   other WTPs.  This would allow the forgery of the source of data-
   channel traffic.  This, however, should not be a surprise for
   unencrypted data channels.  When the data channel is encrypted, the
   Session ID is not exposed, and therefore can safely be used to
   associate a data and control channel.  The 64-bit length of the
   Session ID mitigates online guessing attacks where an adversarial,
   authenticated WTP tries to correlate his own data channel with
   another WTP's control channel.  Note that for encrypted data
   channels, the Session ID should only be used for correlation for the
   first packet immediately after the initial DTLS handshake.  Future
   correlation should instead be done via identification of a packet's
   DTLS session.

12.3.  Discovery or DTLS Setup Attacks

   Since the Discovery Request messages are sent in the clear, it is
   important that AC implementations NOT assume that receiving a
   Discovery Request message from a WTP implies that the WTP has
   rebooted, and consequently tear down any active DTLS sessions.
   Discovery Request messages can easily be spoofed by malicious
   devices, so it is important that the AC maintain two separate sets of
   states for the WTP until the DTLSSessionEstablished notification is
   received, indicating that the WTP was authenticated.  Once a new DTLS
   session is successfully established, any state referring to the old
   session can be cleared.

   Similarly, entering the DTLS Setup phase SHOULD NOT assume that the
   WTP has reset, and therefore should not discard active state until
   the DTLS session has been successfully established.  While the
   HelloVerifyRequest provides some protection against denial of service
   (DoS) attacks on the AC, an adversary capable of receiving packets at
   a valid address (or a malfunctioning or misconfigured WTP) may
   repeatedly attempt DTLS handshakes with the AC, potentially creating
   a resource shortage.  If either the FailedDTLSSessionCount or the
   FailedDTLSAuthFailCount counter reaches the value of
   MaxFailedDTLSSessionRetry variable (see Section 4.8), implementations
   MAY choose to rate-limit new DTLS handshakes for some period of time.
   It is RECOMMENDED that implementations choosing to implement rate
   limiting use a random discard technique, rather than mimicking the
   WTP's sulking behavior.  This will ensure that messages from valid
   WTPs will have some probability of eliciting a response, even in the
   face of a significant DoS attack.

   Some implementations may wish to pass information about clients who
   have passed the discovery phase to the DTLS layer, authorizing only
   those clients to initiate a DTLS handshake.  Note that the impact of
   this on mitigating denial of service attacks against the DTLS layer
   is minimal, because DTLS already uses client-side cookies to minimize



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   processor consumption attacks.  As a result, implementations SHOULD
   NOT maintain state between the discovery and DTLS handshake phases of
   the CAPWAP protocol initialization.

12.4.  Interference with a DTLS Session

   If a WTP or AC repeatedly receives packets which fail DTLS
   authentication or decryption, this could indicate a DTLS
   desynchronization between the AC and WTP, a link prone to
   undetectable bit errors, or an attacker trying to disrupt a DTLS
   session.

   In the state machine (section 2.3), transitions to the DTLS tear down
   state can be triggered by frequently receiving DTLS packets with
   authentication or decryption errors.  The threshold or technique for
   deciding when to move to the tear down state should be chosen
   carefully.  Being able to easily transition to DTLS TD allows easy
   detection of malfunctioning devices, but allows for denial of service
   attacks.  Making it difficult to transition to DTLS TD prevents
   denial of service attacks, but makes it more difficult to detect and
   reset a malfunctioning session.  Implementers should set this policy
   with care.

12.5.  Use of Preshared Keys in CAPWAP

   While use of preshared keys may provide deployment and provisioning
   advantages not found in public key based deployments, it also
   introduces a number of operational and security concerns.  In
   particular, because the keys must typically be entered manually, it
   is common for people to base them on memorable words or phrases.
   These are referred to as "low entropy passwords/passphrases".

   Use of low-entropy preshared keys, coupled with the fact that the
   keys are often not frequently updated, tends to significantly
   increase exposure.  For these reasons, the following recommendations
   are made:

   o  When DTLS is used with a preshared-key (PSK) ciphersuite, each WTP
      SHOULD have a unique PSK.  Since WTPs will likely be widely
      deployed, their physical security is not guaranteed.  If PSKs are
      not unique for each WTP, key reuse would allow the compromise of
      one WTP to result in the compromise of others

   o  Generating PSKs from low entropy passwords is NOT RECOMMENDED.

   o  It is RECOMMENDED that implementations that allow the
      administrator to manually configure the PSK also provide a
      capability for generation of new random PSKs, taking RFC 4086 [2]



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      into account.

   o  Preshared keys SHOULD be periodically updated.  Implementations
      MAY facilitate this by providing an administrative interface for
      automatic key generation and periodic update, or it MAY be
      accomplished manually instead.

   Every pairwise combination of WTP and AC on the network SHOULD have a
   unique PSK.  This prevents the domino effect (see Guidance for AAA
   Key Management [20]).  If PSKs are tied to specific WTPs, then
   knowledge of the PSK implies a binding to a specified identity that
   can be authorized.

   If PSKs are shared, this binding between device and identity is no
   longer possible.  Compromise of one WTP can yield compromise of
   another WTP, violating the CAPWAP security hierarchy.  Consequently,
   sharing keys between WTPs is NOT RECOMMENDED.

12.6.  Use of Certificates in CAPWAP

   For public-key-based DTLS deployments, each device SHOULD have unique
   credentials, with an extended key usage authorizing the device to act
   as either a WTP or AC.  If devices do not have unique credentials, it
   is possible that by compromising one device, any other device using
   the same credential may also be considered to be compromised.

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

   Each device is responsible for authenticating and authorizing devices
   with which they communicate.  Authentication entails validation of
   the chain of trust leading to the peer certificate, followed by the
   peer certificate itself.  Implementations SHOULD also provide a
   secure method for verifying that the credential in question has not
   been revoked.

   Note that if the WTP relies on the AC for network connectivity (e.g.
   the AC is a layer 2 switch to which the WTP is directly connected),
   the WTP may not be able to contact an OCSP server or otherwise obtain
   an up to date CRL if a compromised AC doesn't explicitly permit this.
   This cannot be avoided, except through effective physical security
   and monitoring measures at the AC.

   Proper validation of certificates typically requires checking to
   ensure the certificate has not yet expired.  If devices have a real-
   time clock, they SHOULD verify the certificate validity dates.  If no



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   real-time clock is available, the device SHOULD make a best-effort
   attempt to validate the certificate validity dates through other
   means.  Failure to check a certificate's temporal validity can make a
   device vulnerable to man-in-the-middle attacks launched using
   compromised, expired certificates, and therefore devices should make
   every effort to perform this validation.

12.7.  AAA Security

   The AAA protocol is used to distribute EAP keys to the ACs, and
   consequently its security is important to the overall system
   security.  When used with TLS or IPsec, security guidelines specified
   in RFC 3539 [5] SHOULD be followed.

   In general, the link between the AC and AAA server SHOULD be secured
   using a strong ciphersuite keyed with mutually authenticated session
   keys.  Implementations SHOULD NOT rely solely on Basic RADIUS shared
   secret authentication as it is often vulnerable to dictionary
   attacks, but rather SHOULD use stronger underlying security
   mechanisms.































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13.  Management Considerations

   The CAPWAP protocol assumes that it is the only configuration
   interface to the WTP to configure parameters that are specified in
   the CAPWAP specifications.  While the use of a separate management
   protocol MAY be used for the purposes of monitoring the WTP directly,
   configuring the WTP through a separate management interface is not
   recommended.  Configuring the WTP through a separate protocol, such
   as via a CLI or SNMP, could lead to the AC state being out of sync
   with the WTP.









































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14.  Transport Considerations

   The CAPWAP WG carefully considered the congestion control
   requirements of the CAPWAP protocol, both for the CAPWAP control and
   data channels.

   CAPWAP specifies a single-threaded command/response protocol to be
   used on the control channel, and we have specified that an
   exponential back-off algorithm should be used when commands are
   retransmitted.  When CAPWAP runs in its default mode (Local MAC), the
   control channel is the only CAPWAP channel.

   However, CAPWAP can also be run in Split MAC mode, in which case
   there will be a DTLS-encrypted data channel between each WTP and the
   AC.  The WG discussed various options for providing congestion
   control on this channel.  However, due to performance problems with
   TCP when it is run over another congestion control mechanism and the
   fact that the vast majority of traffic run over the CAPWAP data
   channel is likely to be congestion-controlled IP traffic, the CAPWAP
   WG felt that specifying a congestion control mechanism for the CAPWAP
   data channel would be more likely to cause problems than to resolve
   any.

   Because there is no congestion control mechanism specified for the
   CAPWAP data channel, it is recommended that non-congestion-controlled
   traffic not be tunneled over CAPWAP.  When a significant amount of
   non-congestion-controlled traffic is expected to be present on a
   WLAN, the CAPWAP connection between the AC and the WTP for that LAN
   should be configured to remain in Local MAC mode with Distribution
   function at the WTP.

   The lock step nature of the CAPWAP protocol's control channel can
   cause the firmware download process to take some time, depending upon
   the RTT.  This is not expected to be a problem since the CAPWAP
   protocol allows firmware to be downloaded while the WTP provides
   service to wireless clients/devices.

   It is necessary for the WTP and AC to configure their MTU based on
   the capabilities of the path.  See Section 3.5 for more information.












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15.  IANA Considerations

   A separate UDP port for data channel communications is (currently)
   the selected demultiplexing mechanism, and a port must be assigned
   for this purpose in Section 3.1.  The UDP port numbers are listed by
   IANA at http://www.iana.org/assignments/port-numbers.

   IANA needs to assign an organization local multicast address called
   the "All ACs multicast address" from the IPv6 multicast address
   registry in Section 3.3

15.1.  CAPWAP Message Types

   The Message Type field in the CAPWAP header (Section 4.5.1.1) is used
   to identify the operation performed by the message.  There are
   multiple namespaces, which is identified via the first three octets
   of the field containing the IANA Enterprise Number [10].  When the
   Enterprise Number is set to zero, the message types are reserved for
   use by the base CAPWAP specification which are controlled and
   maintained by IANA and requires a Standards Action.

15.2.  Wireless Binding Identifiers

   The Wireless Binding Identifier (WBID) field in the CAPWAP header
   (Section 4.3) is used to identify the wireless technology associated
   with the packet.  Due to the limited address space available, a new
   WBID request requires Standards Action.
























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16.  Acknowledgements

   The following individuals are acknowledged for their contributions to
   this protocol specification: Puneet Agarwal, Abhijit Choudhury,
   Saravanan Govindan, Peter Nilsson, and David Perkins.

   Michael Vakulenko contributed text to describe how CAPWAP can be used
   over layer 3 (IP/UDP) networks.











































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17.  References

17.1.  Normative References

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

   [2]   Eastlake, D., Schiller, J., and S. Crocker, "Randomness
         Requirements for Security", BCP 106, RFC 4086, June 2005.

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

   [4]   Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
         Public Key Infrastructure Certificate and Certificate
         Revocation List (CRL) Profile", RFC 3280, April 2002.

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

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

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

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

   [9]   Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
         Extensions", RFC 2132, March 1997.

   [10]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434,
         October 1998.

   [11]  Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and G.
         Fairhurst, "The Lightweight User Datagram Protocol (UDP-Lite)",
         RFC 3828, July 2004.

   [12]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
         Discovery", RFC 4821, March 2007.

   [13]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
         Specification", RFC 1883, December 1995.

   [14]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
         November 1990.



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   [15]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery for
         IP version 6", RFC 1981, August 1996.

   [16]  Calhoun, P., "CAPWAP Protocol Binding for IEEE 802.11",
         draft-ietf-capwap-protocol-binding-ieee80211-06 (work in
         progress), February 2008.

   [17]  Calhoun, P., "CAPWAP Access Controller DHCP Option",
         draft-calhoun-dhc-capwap-ac-option-00 (work in progress),
         April 2007.

17.2.  Informational References

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

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

   [20]  Housley, R. and B. Aboba, "Guidance for AAA Key Management",
         draft-housley-aaa-key-mgmt-09 (work in progress),
         February 2007.

   [21]  Modadugu et al, N., "The Design and Implementation of Datagram
         TLS", Feb 2004.

   [22]  IEEE, "Guidelines for use of a 48-bit Extended Unique
         Identifier", Dec 2005.

   [23]  IEEE, "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64)
         REGISTRATION AUTHORITY".




















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Editors' Addresses

   Pat R. Calhoun
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134

   Phone: +1 408-853-5269
   Email: pcalhoun@cisco.com


   Michael P. Montemurro
   Research In Motion
   5090 Commerce Blvd
   Mississauga, ON  L4W 5M4
   Canada

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


   Dorothy Stanley
   Aruba Networks
   1322 Crossman Ave
   Sunnyvale, CA  94089

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























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Full Copyright Statement

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