Network Working Group B. Aboba
Request for Comments: 3162 Microsoft
Category: Standards Track G. Zorn
Cisco Systems
D. Mitton
Circular Logic UnLtd.
August 2001

RADIUS and IPv6

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 Internet Society (2001). All Rights Reserved.

Abstract

This document specifies the operation of RADIUS (Remote
Authentication Dial In User Service) when run over IPv6 as well as
the RADIUS attributes used to support IPv6 network Access.

1. IntrodUCtion

This document specifies the operation of RADIUS [4]-[8] over IPv6
[13] as well as the RADIUS attributes used to support IPv6 network
access.

Note that a NAS sending a RADIUS Access-Request may not know a-priori
whether the host will be using IPv4, IPv6, or both. For example,
within PPP, IPv6CP [11] occurs after LCP, so that address assignment
will not occur until after RADIUS authentication and authorization
has completed.

Therefore it is presumed that the IPv6 attributes described in this
document MAY be sent along with IPv4-related attributes within the
same RADIUS message and that the NAS will decide which attributes to
use. The NAS SHOULD only allocate addresses and prefixes that the
client can actually use, however. For example, there is no need for

the NAS to reserve use of an IPv4 address for a host that only
supports IPv6; similarly, a host only using IPv4 or 6to4 [12] does
not require allocation of an IPv6 prefix.

The NAS can provide IPv6 access natively, or alternatively, via other
methods such as IPv6 within IPv4 tunnels [15] or 6over4 [14]. The
choice of method for providing IPv6 access has no effect on RADIUS
usage per se, although if it is desired that an IPv6 within IPv4
tunnel be opened to a particular location, then tunnel attributes
should be utilized, as described in [6], [7].

1.1. Requirements language

In this document, the key Words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [1].

2. Attributes

2.1. NAS-IPv6-Address

Description

This Attribute indicates the identifying IPv6 Address of the NAS
which is requesting authentication of the user, and SHOULD be
unique to the NAS within the scope of the RADIUS server. NAS-
IPv6-Address is only used in Access-Request packets. NAS-IPv6-
Address and/or NAS-IP-Address MAY be present in an Access-Request
packet; however, if neither attribute is present then NAS-
Identifier MUST be present.

A summary of the NAS-IPv6-Address Attribute format is shown below.
The fields are transmitted from left to right.

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 Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

95 for NAS-IPv6-Address

Length

18

Address

The Address field is 16 octets.

3.2. Framed-Interface-Id

Description

This Attribute indicates the IPv6 interface identifier to be
configured for the user. It MAY be used in Access-Accept packets.
If the Interface-Identifier IPv6CP option [11] has been
successfully negotiated, this Attribute MUST be included in an
Access-Request packet as a hint by the NAS to the server that it
would prefer that value. It is recommended, but not required,
that the server honor the hint.

A summary of the Framed-Interface-Id Attribute format is shown below.
The fields are transmitted from left to right.

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 Interface-Id
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Id
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Id
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

96 for Framed-Interface-Id

Length

10

Interface-Id

The Interface-Id field is 8 octets.

2.3. Framed-IPv6-Prefix

Description

This Attribute indicates an IPv6 prefix (and corresponding route)
to be configured for the user. It MAY be used in Access-Accept
packets, and can appear multiple times. It MAY be used 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. Since it is assumed that the NAS will plumb a
route corresponding to the prefix, it is not necessary for the
server to also send a Framed-IPv6-Route attribute for the same
prefix.

A summary of the Framed-IPv6-Prefix Attribute format is shown below.
The fields are transmitted from left to right.

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

97 for Framed-IPv6-Prefix

Length

At least 4 and no larger than 20.

Reserved

This field, which is reserved and MUST be present, is always set
to zero.

Prefix-Length

The length of the prefix, in bits. At least 0 and no larger than
128.

Prefix

The Prefix field is up to 16 octets in length. Bits outside of
the Prefix-Length, if included, must be zero.

2.4. Login-IPv6-Host

Description

This Attribute indicates the system with which to connect the
user, when the Login-Service Attribute is included. It MAY be
used in Access-Accept packets. It MAY be used in an Access-
Request packet as a hint to the server that the NAS would prefer
to use that host, but the server is not required to honor the
hint.

A summary of the Login-IPv6-Host Attribute format is shown below.
The fields are transmitted from left to right.

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 Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

98 for Login-IPv6-Host

Length

18

Address

The Address field is 16 octets in length. The value
0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF indicates that the NAS SHOULD
allow the user to select an address or name to be connected to.
The value 0 indicates that the NAS SHOULD select a host to connect
the user to. Other values indicate the address the NAS SHOULD
connect the user to.

2.5. Framed-IPv6-Route

Description

This Attribute provides routing information to be configured for
the user on the NAS. It is used in the Access-Accept packet and
can appear multiple times.

A summary of the Framed-IPv6-Route Attribute format is shown below.
The fields are transmitted from left to right.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type Length Text ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Type

99 for Framed-IPv6-Route

Length

>=3

Text

The Text field is one or more octets, and its contents are
implementation dependent. The field is not NUL (hex 00)
terminated. It is intended to be human readable and MUST NOT
affect operation of the protocol.

For IPv6 routes, it SHOULD contain a destination prefix optionally
followed by a slash and a decimal length specifier stating how
many high order bits of the prefix to use. That is followed by a
space, a gateway address, a space, and one or more metrics
(encoded in decimal) separated by spaces. Prefixes and addresses
are formatted as described in [16]. For example,
"2000:0:0:106::/64 2000::106:a00:20ff:fe99:a998 1".

Whenever the gateway address is the IPv6 unspecified address the
IP address of the user SHOULD be used as the gateway address. The
unspecified address can be eXPressed in any of the acceptable
formats described in [16]. For example, "2000:0:0:106::/64 :: 1".

2.6. Framed-IPv6-Pool

Description

This Attribute contains the name of an assigned pool that SHOULD
be used to assign an IPv6 prefix for the user. If a NAS does not
support multiple prefix pools, the NAS MUST ignore this Attribute.

A summary of the Framed-IPv6-Pool Attribute format is shown below.
The fields are transmitted from left to right.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Length String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

100 for Framed-IPv6-Pool

Length

>= 3

String

The string field contains the name of an assigned IPv6 prefix pool
configured on the NAS. The field is not NUL (hex 00) terminated.

3. 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
0-1 0 0 0 0-1 95 NAS-IPv6-Address
0-1 0-1 0 0 0-1 96 Framed-Interface-Id
0+ 0+ 0 0 0+ 97 Framed-IPv6-Prefix
0+ 0+ 0 0 0+ 98 Login-IPv6-Host
0 0+ 0 0 0+ 99 Framed-IPv6-Route
0 0-1 0 0 0-1 100 Framed-IPv6-Pool

4. References

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

[2] Yergeau, F., "UTF-8, a transformation format of Unicode and ISO
10646", RFC2044, October 1996.

[3] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC2607, June 1999.

[4] Rigney, C., Rubens, A., Simpson, W. and S. Willens, "Remote
Authentication Dial In User Service (RADIUS)", RFC2865, June
2000.

[5] Rigney, C., "RADIUS Accounting", RFC2866, June 2000.

[6] Zorn, G., Mitton, D. and B. Aboba, "RADIUS Accounting
Modifications for Tunnel Protocol Support", RFC2867, June
2000.

[7] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M.
and I. Goyret, "RADIUS Attributes for Tunnel Protocol Support",
RFC2868, June 2000.

[8] Rigney, C., Willats, W. and P. Calhoun, "RADIUS Extensions",
RFC2869, June 2000.

[9] Kent S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC2401, November 1998.

[10] Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC2434, October
1998.

[11] HaSKIN, D. and E. Allen, "IP Version 6 over PPP", RFC2472,
December 1998.

[12] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC3056, February 2001.

[13] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC2460, December 1998.

[14] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC2529, March 1999.

[15] Gilligan, R. and E. Nordmark, "Transition Mechanisms for IPv6
Hosts and Routers", RFC2893, August 2000.

[16] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC2373, July 1998.

5. Security Considerations

This document describes the use of RADIUS for the purposes of
authentication, authorization and accounting in IPv6-enabled
networks. In such networks, the RADIUS protocol may run either over
IPv4 or over IPv6. Known security vulnerabilities of the RADIUS
protocol are described in [3], [4] and [8].

Since IPSEC [9] is mandatory to implement for IPv6, it is expected
that running RADIUS implementations supporting IPv6 will typically
run over IPSEC. Where RADIUS is run over IPSEC and where
certificates are used for authentication, it may be desirable to
avoid management of RADIUS shared secrets, so as to leverage the
improved scalability of public key infrastructure.

Within RADIUS, a shared secret is used for hiding of attributes such
as User-Password [4] and Tunnel-Password [7]. In addition, the
shared secret is used in computation of the Response Authenticator
[4], as well as the Message-Authenticator attribute [8]. Therefore,
in RADIUS a shared secret is used to provide confidentiality as well
as integrity protection and authentication. As a result, only use of
IPSEC ESP with a non-null transform can provide security services
sufficient to substitute for RADIUS application-layer security.
Therefore, where IPSEC AH or ESP null is used, it will typically
still be necessary to configure a RADIUS shared secret.

However, where RADIUS is run over IPSEC ESP with a non-null
transform, the secret shared between the NAS and the RADIUS server
MAY NOT be configured. In this case, a shared secret of zero length
MUST be assumed.

6. IANA Considerations

This document requires the assignment of six new RADIUS attribute
numbers for the following attributes:

NAS-IPv6-Address
Framed-Interface-Id
Framed-IPv6-Prefix
Login-IPv6-Host
Framed-IPv6-Route
Framed-IPv6-Pool

See section 3 for the registered list of numbers.

7. Acknowledgments

The authors would like to acknowledge Jun-ichiro itojun Hagino of IIJ
Research Laboratory, Darran Potter of Cisco and Carl Rigney of Lucent
for contributions to this document.

8. Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 936 6605
Fax: +1 425 936 7329
EMail: bernarda@microsoft.com

Glen Zorn
Cisco Systems, Inc.
500 108th Avenue N.E., Suite 500
Bellevue, WA 98004

Phone: +1 425 471 4861
EMail: gwz@cisco.com

Dave Mitton
Circular Logic UnLtd.
733 Turnpike Street #154
North Andover, MA 01845

Phone: 978 683-1814
Email: david@mitton.com

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