Network Working Group K. Chowdhury
Internet-Draft Nortel Networks
Expires: April 26, 2005 A. Lior
Bridgewater Systems
October 26, 2004
RADIUS Attributes for Mobile IPv6 bootstrapping
draft-chowdhury-mip6-bootstrap-radius-01.txt
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines new attributes to facilitate Mobile IPv6
bootstrapping via a RADIUS infrastructure. In an access network
where the user attaches to get IPv6 access, there may be a Network
Access Server (NAS) or an Access Gateway that will require
authentication and authorization. In some cases, this type of access
authentication takes place via RADIUS infrastructure. As part of the
authentication setup the NAS may receive useful configuration
information from the home RADIUS server of the user. In case of
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Mobile IPv6 access, the Home RADIUS server may assign various
information relevant to the user's device for bootstrapping.
Table of Contents
1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Home Agent . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Home Link Prefix . . . . . . . . . . . . . . . . . . . . . 5
2.3 Home Address . . . . . . . . . . . . . . . . . . . . . . . 5
2.4 Authenticity payload . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. RADIUS attributes to carry Mobile IPv6 parameters . . . . . . 7
4.1 Home Agent Attribute . . . . . . . . . . . . . . . . . . . 7
4.2 Home Link Prefix Attribute . . . . . . . . . . . . . . . . 8
4.3 Home Address . . . . . . . . . . . . . . . . . . . . . . . 8
4.4 MIP6 Parameter Authenticity Attribute . . . . . . . . . . 9
5. Table of Attributes . . . . . . . . . . . . . . . . . . . . . 11
6. MN Considerations . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. Normative References . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 16
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1. Motivation
Mobile IPv6 specification [RFC3775] requires a Mobile Node (MN) to
perform registration with a Home Agent with information about its
current point of attachment (Care-of Address). The Home Agent
creates and maintains binding between the MN's Home Address and the
MN's Care-of Address.
In order to register with a Home Agent, the MN needs to know
information such as, the Home Link prefix, the Home Agent Address,
the Home Address, the Home Link prefix Length etc.
The aforementioned set of information may be statically provisioned
in the MN. However, static provisioning of this information has its
drawbacks. It increases provisioning and network maintenance burden
for the operator. Moreover, static provisioning does not allow load
balancing, failover, opportunistic home link assignment etc. For
example, the user may be accessing the network from a location that
may be geographically far away from the preconfigured home link; or
the cost of the link between the NAS and the Home Link is too great.
In these situations static provisioning may not be desirable.
Dynamic assignment of Mobile IPv6 home registration information is a
desirable feature for ease of deployment and network maintenance.
For this purpose, the RADIUS infrastructure, which is used for access
authentication, can be leveraged to assign some or all of the
necessary parameters. The RADIUS server in the Serving or Home
Mobility Service Provider's network (RADIUS-MIP) may return these
parameters to the NAS.
The NAS may convey the received information to the MN using various
techniques. One such technique may utilize the role of the NAS as a
relay agent for Dynamic Host Configuration Protocol. In this case,
upon receiving the information from the RADIUS-MIP server, the NAS
forwards the set of parameters to the DHCP Client along with REPLY or
ADVERTISE messages [MIP6-DHC-AGENTOP].
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2. Overview
|
Access Service Provider | Serving or Home Mobility
| Service Provider
|
+-------+ | +-------+
| | | | |
|Access |----------|--------|RADIUS |
|RADIUS | | | -MIP |
| | | | |
+-------+ | +-------+
| |
| |
| |
| |
| |
| |
| |
+-----+ | +-----+
+----+ | | | | Home|
| MN |--------------| NAS/| | |Agent|
+----+ |Relay| | | |
+-----
+ | +-----+
In the typical Mobile IPv6 access scenario as shown above, the MN
attaches in a Access Service Provider's network. During this attach
procedure, the NAS or the Access Router authenticates and authorizes
the MN for IPv6 access service. In the scenario shown, the
authentication and authorization happens via a RADIUS infrastructure.
At the time of authorizing the user for IPv6 access, the RADIUS
server in the Home or Serving Mobility Service Provider's (MSP)
network (RADIUS-MIP) detects that the user is authorized for Mobile
IPv6 access. Based on the MSP's policy, the RADIUS-MIP server may
allocate several parameters to the MN for use during the subsequent
Mobile IPv6 registration. A list of such parameters is described in
the following sub sections.
2.1 Home Agent
The Home or the Serving MSP may decide to assign a Home Agent to the
MN that is in close proximity to the point of attachment (e.g.
determined by the NAS-ID). There may be other reasons for assigning
Home Agents to the MN, e.g. load sharing in the network. The
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attribute also contains the prefix length so that the MN can easily
infer the Home Link prefix from the Home Agent address.
2.2 Home Link Prefix
For the same reason as the HA assignment, the Home or the Serving MSP
may assign a Home Link that is in close proximity to the point of
attachment (NAS-ID). The MN can perform [RFC3775] specific
procedures to discover other information for Mobile IPv6
registration.
2.3 Home Address
The RADIUS-MIP server may assign a Home Address to the MN. This
allows the network operator to support mobile devices that are not
configured with static addresses. The attribute also contains the
prefix length so that the MN can easily infer the Home Link prefix
from the Home Agent address.
2.4 Authenticity payload
The RADIUS-MIP server includes a secure hash of all the MIP6 related
assigned parameters. The secure hash is computed with the shared
secret that the RADIUS-MIP has with the MN. This helps maintain the
integrity of the assigned values while the Access Service Provider
and the Mobility Service Provider do not a share trust relationship.
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3. Terminology
The keywords "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.
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4. RADIUS attributes to carry Mobile IPv6 parameters
This section defines format and syntax for the attribute that carries
the Mobile IPv6 parameters described in section 2.
The attributes MAY be present in Access-Accept, Accounting-Request.
4.1 Home Agent Attribute
This attribute is sent by the RADIUS-MIP server to the NAS in an
Access-Accept message. The attribute carries the assigned Home Agent
address.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| IPv6 address of assigned Home Agent |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
ASSIGNED-HA-TYPE to be defined by IANA.
Length:
= 20 octets
Reserved:
Reserved for future use. All bits set to 0.
Prefix-Length:
This field indicates the prefix length of the Home Link.
IPv6 address of assigned Home Agent:
128-bit IPv6 address of the assigned Home Agent.
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4.2 Home Link Prefix Attribute
This attribute is sent by the RADIUS-MIP server to the NAS in an
Access-Accept message. The attribute carries the assigned Home Link
prefix.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Home Link Prefix |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
ASSIGNED-HL-TYPE to be defined by IANA.
Length:
>= 4 octets + the minimum length of a prefix.
Reserved:
Reserved for future use. All bits set to 0.
Home Link Prefix:
Home Link prefix (upper order bits) of the assigned Home Link
where the MN should send binding update.
4.3 Home Address
This attribute is sent by the RADIUS server to the NAS in an
Access-Accept message. The attribute carries the assigned Home IPv6
Address for the MN.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Assigned IPv6 Home Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
ASSIGNED-HOA-TYPE to be defined by IANA.
Length:
= 20 octets.
Reserved:
Reserved for future use. All bits set to 0.
Prefix-Length:
This field indicates the prefix length of the Home Link.
Assigned IPv6 Home Address:
IPv6 Home Address that is assigned to the MN.
4.4 MIP6 Parameter Authenticity Attribute
This attribute is sent by the RADIUS-MIP server to the NAS in an
Access-Accept message. The attribute carries a authenticator to
validate the integrity of the MIP6 parameters that are assigned by
the RADIUS-MIP server. The authenticator is calculated by taking
HMAC-SHA-1 of the all the MIP6 related assigned parameter values and
a shared secret that the RADIUS-MIP server has for the MN.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Authenticator |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
MIP6-PARM-AUTH-TYPE to be defined by IANA.
Length:
= 20 octets.
Reserved:
Reserved for future use. All bits set to 0.
Authenticator:
HMAC-SHA-1 (shared secret between the MN and the RADIUS-MIP,
assigned MIP6 values).
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5. Table of Attributes
The following table provides a guide to which attributes may be found
in RADIUS message and in what number.
Request Accept Reject Challenge # Attribute
0 0-1 0 0 TBD Home Agent
0 0-1 0 0 TBD Home Link Prefix
0 0-1 0 0 TBD Home Address
0 0-1 0 0 TBD MIP6 Parameter
Authenticity
The following table defines the meaning of the above table entries.
0 This attribute MUST NOT be present.
0-1 Zero or one instance of this attribute MAY be present.
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6. MN Considerations
Upon receiving the MIP6 parameters from the network via mechanisms
such as [MIP6-DHC-AGENTOP] the MN MUST check whether the parameter
set contains the MIP6 Parameter Authenticity value. If yes, the MN
MUST compute a secure hash as following:
HMAC-SHA-1 (shared secret between the MN and the RADIUS-MIP, received
MIP6 values)
The MN matchs the output of the above hash with the MIP6 Parameter
Authenticity value received from the network. If the values match
the MN accept the received MIP6 parameters to be from a trusted
source. If the comparison results in a mismatch, the MN MUST
silently discard the received MIP6 parameters.
If the received MIP6 parameter set does not contain the MIP6
Parameter Authenticity value, the MN MAY accept the received MIP6
parameters.
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7. Security Considerations
Assignment of these values to a user should be based on successful
authentication of the user's access at the NAS. The RADIUS-MIP
server should only assign these values to an user who is authorized
for Mobile IPv6 service (this check could be performed with the
user's subscription profile in the Home Network).
The NAS to the Home RADIUS server transactions must be adequately
secured. Otherwise there is a possibility that the user may receive
fraudulent values from a rogue RADIUS server potentially hijacking
the user's Mobile IPv6 session.
If the RADIUS-MIP server has a shared secret with the MN, the
RADIUS-MIP server MUST include the MIP6 Parameter Authenticity
attribute while assigning other MIP6 bootstrap information to the MN.
This enables the MN to verify that the received MIP6 bootstrap
information is from a trusted source.
These new attributes do not involve additional security
considerations besides the one identified in [RFC2865].
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8. IANA Considerations
The RADIUS attribute types: ASSIGNED-HA-TYPE, ASSIGNED-HL-TYPE,
ASSIGNED-HOA-TYPE, and MIP6-PARM-AUTH-TYPE MUST be assigned by IANA.
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9. Acknowledgements
Thanks to the following individuals for their review and constructive
comments during the development of this document:
Mark Watson, Jayshree Bharatia.
10 Normative References
[MIP6-DHC-AGENTOP]
Chowdhury et. al., K., "DHCP Relay Agent Option to Support
Mobile IPv6 bootstrapping",
draft-chowdhury-dhc-mip6-agentop-00.txt (work in
progress), October 2004.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
Authors' Addresses
Kuntal Chowdhury
Nortel Networks
2221 Lakeside Blvd.
Richardson, TX 75082
US
Phone: +1 972-685-7788
EMail: chowdury@nortelnetworks.com
Avi Lior
Bridgewater Systems
303 Terry Fox Drive, Suite 100
Ottawa, Ontario
Canada K2K 3J1
Phone: +1 613-591-6655
EMail: avi@bridgewatersystems.com
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