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RFC 4818 PROPOSED STANDARD RADIUS · IPV6 · PROVISIONING

RADIUS Delegated-IPv6-Prefix Attribute

A RADIUS attribute that tells an access server which IPv6 prefix to hand to a customer's own network.

On rfc-editor.org ↗
PUBLISHED
April 2007
AUTHORS
J. Salowey, R. Droms
STREAM
IETF
ATTRIBUTE TYPE
123
ATTRIBUTE LENGTH
4 to 20 bytes
PREFIX-LENGTH
0 to 128 bits
DIAMETER DATA TYPE
OctetString
DOI
10.17487/RFC4818

RFC text

Contents
Original text · RFC Editor View on rfc-editor.org ↗ 
Network Working Group                                         J. Salowey
Request for Comments: 4818                                      R. Droms
Category: Standards Track                            Cisco Systems, Inc.
                                                              April 2007


                 RADIUS Delegated-IPv6-Prefix Attribute

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.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document defines a RADIUS (Remote Authentication Dial In User
   Service) attribute that carries an IPv6 prefix that is to be
   delegated to the user.  This attribute is usable within either RADIUS
   or Diameter.

1.  Introduction

   This document defines the Delegated-IPv6-Prefix attribute as a RADIUS
   [1] attribute that carries an IPv6 prefix to be delegated to the
   user, for use in the user's network.  For example, the prefix in a
   Delegated-IPv6-Prefix attribute can be delegated to another node
   through DHCP Prefix Delegation [2].

   The Delegated-IPv6-Prefix attribute can be used in DHCP Prefix
   Delegation between the delegating router and a RADIUS server, as
   illustrated in the following message sequence.


   Requesting Router   Delegating Router                   RADIUS Server
         |                     |                                 |
         |-Solicit------------>|                                 |
         |                     |-Request------------------------>|
         |                     |<--Accept(Delegated-IPv6-Prefix)-|
         |<--Advertise(Prefix)-|                                 |
         |-Request(Prefix)---->|                                 |
         |<--Reply(Prefix)-----|                                 |
         |                     |                                 |
                DHCP PD                      RADIUS


   The Framed-IPv6-Prefix attribute [4] is not designed to support
   delegation of IPv6 prefixes to be used in the user's network, and
   therefore Framed-IPv6-Prefix and Delegated-IPv6-Prefix attributes may
   be included in the same RADIUS packet.

2.  Terminology

   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 [3].

3.  Attribute Format

   The format of the Delegated-IPv6-Prefix is:

       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     |  Reserved     | Prefix-Length |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   Prefix
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   Prefix
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   Prefix
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   Prefix                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type

           123 for Delegated-IPv6-Prefix

      Length

           The length of the entire attribute, in bytes.  At least 4 (to
           hold Type/Length/Reserved/Prefix-Length for a 0-bit prefix),
           and no larger than 20 (to hold Type/Length/ Reserved/Prefix-
           Length for a 128-bit prefix)

      Reserved

           Always set to zero by sender; ignored by receiver

      Prefix-Length

           The length of the prefix being delegated, in bits.  At least
           0 and no larger than 128 bits (identifying a single IPv6
           address)

   Note that the prefix field is only required to be long enough to hold
   the prefix bits and can be shorter than 16 bytes.  Any bits in the
   prefix field that are not part of the prefix MUST be zero.

   The Delegated-IPv6-Prefix MAY appear in an Access-Accept packet, and
   can appear multiple times.  It MAY appear in an Access-Request packet
   as a hint by the NAS to the server that it would prefer these
   prefix(es), but the server is not required to honor the hint.

   The Delegated-IPv6-Prefix attribute MAY appear in an Accounting-
   Request packet.

   The Delegated-IPv6-Prefix MUST NOT appear in any other RADIUS
   packets.

4.  Table of Attributes

   The following table provides a guide to which attributes may be found
   in which kinds of packets, and in what quantity.

   +-------------------------------------------------------------------+
   | Request Accept Reject Challenge Accounting  #   Attribute         |
   |                                 Request                           |
   | 0+      0+     0      0         0+          123 Delegated-IPv6-   |
   |                                                 Prefix            |
   +-------------------------------------------------------------------+

   The meaning of the above table entries is as follows:
      0   This attribute MUST NOT be present.
      0+  Zero or more instances of this attribute MAY be present.
      0-1 Zero or one instance of this attribute MAY be present.
      1   Exactly one instance of this attribute MUST be present.
      1+  One or more of these attributes MUST be present.

5.  Diameter Considerations

   When used in Diameter, the attribute defined in this specification
   can be used as a Diameter AVP from the Code space 1-255, i.e., RADIUS
   attribute compatibility space.  No additional Diameter Code values
   are therefore allocated.  The data types of the attributes are as
   follows:

        Delegated-IPv6-Prefix             OctetString

   The attribute in this specification has no special translation
   requirements for Diameter to RADIUS or RADIUS to Diameter gateways,
   i.e., the attribute is copied as is, except for changes relating to
   headers, alignment, and padding.  See also RFC 3588 [5], Section 4.1,
   and RFC 4005 [6], Section 9.

   The text in this specification describing the applicability of the
   Delegated-IPv6-Prefix attribute for RADIUS Access-Request applies in
   Diameter to AA-Request [6] or Diameter-EAP-Request [7].

   The text in this specification describing the applicability of the
   Delegated-IPv6-Prefix attribute for RADIUS Access-Accept applies in
   Diameter to AA-Answer or Diameter-EAP-Answer that indicates success.

   The text in this specification describing the applicability of the
   Delegated-IPv6-Prefix attribute for RADIUS Accounting-Request applies
   to Diameter Accounting-Request [6] as well.

   The AVP flag rules [5] for the Delegated-IPv6-Prefix attribute are:

                                      +---------------------+
                                      |    AVP Flag rules   |
                                      |----+-----+----+-----|----+
                     AVP              |    |     |SHLD| MUST|    |
     Attribute Name  Code  Value Type |MUST| MAY | NOT|  NOT|Encr|
     ---------------------------------|----+-----+----+-----|----|
     Delegated-IPv6- 123   OctetString| M  |  P  |    |  V  | Y  |
       Prefix                         |    |     |    |     |    |
     ---------------------------------|----+-----+----+-----|----|

6.  IANA Considerations

   IANA assigned a Type value, 123, for this attribute from the RADIUS
   Attribute Types registry.

7.  Security Considerations

   Known security vulnerabilities of the RADIUS protocol are discussed
   in RFC 2607 [8], RFC 2865 [1], and RFC 2869 [9].  Use of IPsec [10]
   for providing security when RADIUS is carried in IPv6 is discussed in
   RFC 3162.

   Security considerations for the Diameter protocol are discussed in
   RFC 3588 [5].

8.  References

8.1.  Normative References

   [1]  Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
        Authentication Dial In User Service (RADIUS)", RFC 2865, June
        2000.

   [2]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
        Configuration Protocol (DHCP) version 6", RFC 3633, December
        2003.

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

9.2.  Informative References

   [4]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 3162,
        August 2001.

   [5]  Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
        "Diameter Base Protocol", RFC 3588, September 2003.

   [6]  Calhoun, P., Zorn, G., Spence, D., and D. Mitton, "Diameter
        Network Access Server Application", RFC 4005, August 2005.

   [7]  Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
        Authentication Protocol (EAP) Application", RFC 4072, August
        2005.

   [8]  Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
        Implementation in Roaming", RFC 2607, June 1999.

   [9]  Rigney, C., Willats, W., and P. Calhoun, "RADIUS Extensions",
        RFC 2869, June 2000.

   [10] Kent, S. and K. Seo, "Security Architecture for the Internet
        Protocol", RFC 4301, December 2005.

Authors' Addresses

   Joe Salowey
   Cisco Systems, Inc.
   2901 Third Avenue
   Seattle, WA  98121
   USA

   Phone: +1 206.310.0596
   EMail: jsalowey@cisco.com


   Ralph Droms
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Phone: +1 978.936.1674
   EMail: rdroms@cisco.com

Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

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   Internet Society.

AI ELI5

On this page
PROBLEMAn existing RADIUS attribute for IPv6 prefixes was not designed to carry a prefix delegated for use inside the user's own network.
MECHANISMRFC 4818 defines attribute type 123, Delegated-IPv6-Prefix, holding a prefix length from 0 to 128 bits and only as many prefix bytes as needed.
WHY IT MATTERSA delegating router can learn from the RADIUS server which prefix to pass on through DHCP Prefix Delegation. The attribute also works in Diameter.

§1Why a New Attribute

RFC 4818 defines the Delegated-IPv6-Prefix attribute for RADIUS. It carries an IPv6 prefix that is to be delegated to the user, for use in the user's network. For example, the prefix can be handed to another node through DHCP Prefix Delegation (RFC 3633).

The existing Framed-IPv6-Prefix attribute is not designed to support delegation of prefixes for the user's network. For that reason, a RADIUS packet may contain both Framed-IPv6-Prefix and Delegated-IPv6-Prefix.

There was already a label for the address block used on the connection itself. The home network needs its own block, so a second label was added.

§2Attribute Format

The attribute has four header fields followed by the prefix. Type is 123. Length is the length of the whole attribute in bytes, at least 4 (a 0-bit prefix) and no larger than 20 (a 128-bit prefix). Reserved is always set to zero by the sender and ignored by the receiver. Prefix-Length is the length of the delegated prefix in bits, from 0 to 128.

The prefix field only needs to be long enough to hold the prefix bits, so it can be shorter than 16 bytes. Any bits in it that are not part of the prefix MUST be zero.

The label says what kind of note it is, how long it is, and how much of the address block is yours. Short blocks use a shorter label.

DELEGATED-IPV6-PREFIX ATTRIBUTE (RFC 4818)
081624
TYPE123LENGTHRESERVEDPREFIX-LENGTH
FieldNameSizeValueDescription
TYPEType1 byte123123 for Delegated-IPv6-Prefix.
LENGTHLength1 byteWhole attribute in bytes, from 4 to 20.
RESERVEDReserved1 byteZero from sender; ignored by receiver.
PREFIX-LENGTHPrefix-Length1 bytePrefix length in bits, 0 to 128.

§3Where the Attribute Can Appear

In an Access-Accept packet the attribute MAY appear, and it can appear multiple times. In an Access-Request it MAY appear as a hint from the NAS that it would prefer those prefixes, but the server is not required to honor the hint. It MAY also appear in an Accounting-Request. It MUST NOT appear in any other RADIUS packet.

The RFC's example shows a requesting router sending a DHCP Solicit to the delegating router. The delegating router asks the RADIUS server, which answers with an Accept carrying the attribute. The delegating router then advertises the prefix and completes the DHCP exchange with a Reply.

The access server can ask for a favorite block, but the company's computer makes the final decision and writes it in the approval note.

DHCP PD WITH RADIUS (RFC 4818 INTRODUCTION)
Requesting RouterDelegating RouterRADIUS Server
  1. Solicit
  2. Request
  3. Accept (Delegated-IPv6-Prefix)
  4. Advertise (Prefix)
  5. Request (Prefix)
  6. Reply (Prefix)

§4Use in Diameter

In Diameter the attribute is an AVP from code space 1-255, the RADIUS attribute compatibility space, so no new Diameter code is allocated. Its data type is OctetString, and the AVP flag rules are M for MUST and P for MAY, with encryption set to Y.

The attribute needs no special translation between Diameter and RADIUS. It is copied as is, apart from changes to headers, alignment and padding. The RADIUS rules for Access-Request, Access-Accept and Accounting-Request apply to the matching Diameter messages.

A newer system called Diameter can read the same label without any translation.

§5Security and IANA Notes

The RFC adds no new security mechanism. It points to known RADIUS vulnerabilities discussed in RFC 2607, RFC 2865 and RFC 2869, and to RFC 3162 for using IPsec to protect RADIUS carried over IPv6. Diameter security is covered in RFC 3588.

On the IANA side, type value 123 was assigned from the RADIUS Attribute Types registry.

This label does not add new locks. It relies on the protections that the existing system already has.

§6References

[1]RFC 2865Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000.June 2000[2]RFC 3633Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.December 2003[4]RFC 3162Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC 3162, August 2001.August 2001[5]RFC 3588Calhoun, P., et al., "Diameter Base Protocol", RFC 3588, September 2003.September 2003