





Network Working Group                                         P. Calhoun
Request for Comments: 5417                           Cisco Systems, Inc.
Category: Standards Track                                     March 2009


      Control And Provisioning of Wireless Access Points (CAPWAP)
                     Access Controller DHCP Option

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

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Abstract

   The Control And Provisioning of Wireless Access Points Protocol
   allows a Wireless Termination Point to use DHCP to discover the
   Access Controllers to which it is to connect.  This document
   describes the DHCP options to be used by the CAPWAP Protocol.






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RFC 5417                 CAPWAP AC DHCP Option                March 2009


Table of Contents

   1. Introduction ....................................................2
      1.1. Conventions Used in This Document ..........................2
      1.2. Terminology ................................................2
   2. CAPWAP AC DHCPv4 Option .........................................2
   3. CAPWAP AC DHCPv6 Option .........................................3
   4. IANA Considerations .............................................5
   5. Security Considerations .........................................5
   6. Acknowledgments .................................................5
   7. References ......................................................5
      7.1. Normative References .......................................5
      7.2. Informative References .....................................6

1.  Introduction

   The Control And Provisioning of Wireless Access Points Protocol
   (CAPWAP) [RFC5415] allows a Wireless Termination Point (WTP) to use
   DHCP to discover the Access Controllers (AC) to which it is to
   connect.

   Prior to the CAPWAP Discovery process, the WTP may use one of many
   methods to identify the proper AC with which to establish a CAPWAP
   connection.  One of these methods is through the DHCP protocol.  This
   is done through the CAPWAP AC DHCPv4 or CAPWAP AC DHCPv6 Option.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Terminology

   This document uses terminology defined in [RFC3753], [RFC2131],
   [RFC3315], and [RFC5415].

2.  CAPWAP AC DHCPv4 Option

   This section defines a DHCPv4 option that carries a list of 32-bit
   (binary) IPv4 addresses indicating one or more CAPWAP ACs available
   to the WTP.









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RFC 5417                 CAPWAP AC DHCP Option                March 2009


   The DHCPv4 option for CAPWAP has the format shown in the following
   figure:

         0                   1
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  option-code  | option-length |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                               |
         +       AC IPv4 Address         +
         |                               |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |             ...               |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:   OPTION_CAPWAP_AC_V4 (138)

   option-length:   Length of the 'options' field in octets; MUST be a
      multiple of four (4).

   AC IPv4 Address:  IPv4 address of a CAPWAP AC that the WTP may use.
      The ACs are listed in the order of preference for use by the WTP.

   A DHCPv4 client, acting on behalf of a CAPWAP WTP, MUST request the
   CAPWAP AC DHCPv4 Option in a Parameter Request List Option, as
   described in [RFC2131] and [RFC2132].

   A DHCPv4 server returns the CAPWAP AC Option to the client if the
   server policy is configured appropriately and the server is
   configured with a list of CAPWAP AC addresses.

   A CAPWAP WTP, acting as a DHCPv4 client, receiving the CAPWAP AC
   DHCPv4 Option MAY use the (list of) IP address(es) to locate an AC.
   The CAPWAP Protocol [RFC5415] provides guidance on the WTP's
   discovery process.

   The WTP, acting as a DHCPv4 client, SHOULD try the records in the
   order listed in the CAPWAP AC DHCPv4 Option received from the DHCPv4
   server.

3.  CAPWAP AC DHCPv6 Option

   This section defines a DHCPv6 option that carries a list of 128-bit
   (binary) IPv6 addresses indicating one or more CAPWAP ACs available
   to the WTP.






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RFC 5417                 CAPWAP AC DHCP Option                March 2009


   The DHCPv6 option for CAPWAP has the format shown in the following
   figure:

       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       option-code             |       option-length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                          AC IPv6 Address                      +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          ....                                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code:   OPTION_CAPWAP_AC_V6 (52)

   option-length:   Length of the 'options' field in octets; MUST be a
      multiple of sixteen (16).

   AC IPv6 Address:  IPv6 address of a CAPWAP AC that the WTP may use.
      The ACs are listed in the order of preference for use by the WTP.

   A DHCPv6 client, acting on behalf of a CAPWAP WTP, MUST request the
   CAPWAP AC DHCPv6 Option in a Parameter Request List Option, as
   described in [RFC3315].

   A DHCPv6 server returns the CAPWAP AC Option to the client if the
   server policy is configured appropriately and the server is
   configured with a list of CAPWAP AC addresses.

   A CAPWAP WTP, acting as a DHCPv6 client, receiving the CAPWAP AC
   DHCPv6 Option MAY use the (list of) IP address(es) to locate an AC.
   The CAPWAP Protocol [RFC5415] provides guidance on the WTP's
   discovery process.

   The WTP, acting as a DHCPv6 client, SHOULD try the records in the
   order listed in the CAPWAP AC DHCPv6 Option received from the DHCPv6
   server.








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RFC 5417                 CAPWAP AC DHCP Option                March 2009


4.  IANA Considerations

   The following DHCPv4 option code for CAPWAP AC Options has been
   assigned by IANA:

           Option Name            Value       Described in
           -----------------------------------------------
           OPTION_CAPWAP_AC_V4    138         Section 2

   The following DHCPv6 option code for CAPWAP AC Options has been
   assigned by IANA:

           Option Name             Value       Described in
           ------------------------------------------------
           OPTION_CAPWAP_AC_V6      52         Section 3

5.  Security Considerations

   The security considerations in [RFC2131], [RFC2132], and [RFC3315]
   apply.  If an adversary manages to modify the response from a DHCP
   server or insert its own response, a WTP could be led to contact a
   rogue CAPWAP AC, possibly one that then intercepts call requests or
   denies service.  CAPWAP's use of Datagram Transport Layer Security
   (DTLS) MUST be used to authenticate the CAPWAP peers in the
   establishment of the session.

   In most of the networks, the DHCP exchange that delivers the options
   prior to network access authentication is neither integrity protected
   nor origin authenticated.  Therefore, in security sensitive
   environments, the options defined in this document SHOULD NOT be the
   only methods used to determine to which AC a WTP should connect.  The
   CAPWAP protocol [RFC5415] defines other AC discovery procedures a WTP
   MAY utilize.

6.  Acknowledgments

   The following individuals are acknowledged for their contributions to
   this protocol specification: Ralph Droms, Margaret Wasserman.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.



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RFC 5417                 CAPWAP AC DHCP Option                March 2009


   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC5415]  Montemurro, M., Stanley, D., and P. Calhoun, "CAPWAP
              Protocol Specification", RFC 5415, March 2009.

7.2.  Informative References

   [RFC3753]  Manner, J. and M. Kojo, "Mobility Related Terminology",
              RFC 3753, June 2004.

Author's Address

   Pat R. Calhoun
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134

   Phone: +1 408-902-3240
   EMail: pcalhoun@cisco.com



























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