Network Working Group P. Calhoun

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.

Calhoun Standards Track [Page 1]

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: [email protected]

Calhoun Standards Track [Page 6]