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Network Working Group                                         P. CalhounRequest for Comments: 5417                           Cisco Systems, Inc.Category: Standards Track                                     March 2009Control And Provisioning of Wireless Access Points (CAPWAP)Access Controller DHCP OptionStatus 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.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.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.Calhoun                     Standards Track                     [Page 1]

RFC 5417                 CAPWAP AC DHCP Option                March 2009Table of Contents1. Introduction ....................................................21.1. Conventions Used in This Document ..........................21.2. Terminology ................................................22. CAPWAP AC DHCPv4 Option .........................................23. CAPWAP AC DHCPv6 Option .........................................34. IANA Considerations .............................................55. Security Considerations .........................................56. Acknowledgments .................................................57. References ......................................................57.1. Normative References .......................................57.2. Informative References .....................................61.  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 inRFC 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.Calhoun                     Standards Track                     [Page 2]

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.Calhoun                     Standards Track                     [Page 3]

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.Calhoun                     Standards Track                     [Page 4]

RFC 5417                 CAPWAP AC DHCP Option                March 20094.  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    138Section 2   The following DHCPv6 option code for CAPWAP AC Options has been   assigned by IANA:           Option Name             Value       Described in           ------------------------------------------------           OPTION_CAPWAP_AC_V6      52Section 35.  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.  References7.1.  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.Calhoun                     Standards Track                     [Page 5]

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.comCalhoun                     Standards Track                     [Page 6]