RFC 6519 PROPOSED STANDARD RADIUS · IPV6 TRANSITION · DS-LITE
RADIUS for DS-Lite: RADIUS Extensions for Dual-Stack Lite
A RADIUS attribute that hands a home gateway's tunnel endpoint name from the provider's AAA server to the access server.
RFC EDITOR
Maglione, R. and A. Durand, "RADIUS Extensions for Dual-Stack Lite", RFC 6519, DOI 10.17487/RFC6519, February 2012, <https://www.rfc-editor.org/info/rfc6519>.
BIBTEX
@misc{rfc6519,
series = {Request for Comments},
number = 6519,
howpublished = {RFC 6519},
publisher = {RFC Editor},
doi = {10.17487/RFC6519},
url = {https://www.rfc-editor.org/info/rfc6519},
author = {R. Maglione and A. Durand},
title = {{RADIUS Extensions for Dual-Stack Lite}},
pagetotal = 11,
year = 2012,
month = feb,
} RFC text
Contents
Internet Engineering Task Force (IETF) R. Maglione
Request for Comments: 6519 Telecom Italia
Category: Standards Track A. Durand
ISSN: 2070-1721 Juniper Networks
February 2012
RADIUS Extensions for Dual-Stack Lite
Abstract
Dual-Stack Lite is a solution to offer both IPv4 and IPv6
connectivity to customers that are addressed only with an IPv6
prefix. Dual-Stack Lite requires pre-configuration of the Dual-Stack
Lite Address Family Transition Router (AFTR) tunnel information on
the Basic Bridging BroadBand (B4) element. In many networks, the
customer profile information may be stored in Authentication,
Authorization, and Accounting (AAA) servers, while client
configurations are mainly provided through the Dynamic Host
Configuration Protocol (DHCP). This document specifies a new Remote
Authentication Dial-In User Service (RADIUS) attribute to carry the
Dual-Stack Lite AFTR tunnel name; the RADIUS attribute is defined
based on the equivalent DHCPv6 OPTION_AFTR_NAME option. This RADIUS
attribute is meant to be used between the RADIUS server and the
Network Access Server (NAS); it is not intended to be used directly
between the B4 element and the RADIUS server.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6519.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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than English.
Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................4
3. DS-Lite Configuration with RADIUS and DHCPv6 ....................4
4. RADIUS Attribute ................................................7
4.1. DS-Lite-Tunnel-Name ........................................7
5. Table of Attributes .............................................9
6. Security Considerations .........................................9
7. IANA Considerations .............................................9
8. References .....................................................10
8.1. Normative References ......................................10
8.2. Informative References ....................................10
1. Introduction
Dual-Stack Lite [RFC6333] is a solution to offer both IPv4 and IPv6
connectivity to customers that are addressed only with an IPv6 prefix
(no IPv4 address is assigned to the attachment device). One of its
key components is an IPv4-over-IPv6 tunnel, but a Dual-Stack-Lite
Basic Bridging BroadBand (B4) element will not know if the network to
which it is attached offers Dual-Stack Lite support. Even if the B4
did know, it would not know the remote end of the tunnel to which it
could establish a connection.
To inform the B4 element of the location of the Address Family
Transition Router (AFTR), a Fully Qualified Domain Name (FQDN) may be
used. Once this information is conveyed, the presence of the
configuration indicating the AFTR's location also informs a host to
initiate Dual-Stack Lite (DS-Lite) service and become a Softwire
Initiator.
[RFC6334] specifies a DHCPv6 option that is meant to be used by a
DS-Lite client (B4 element) to discover its AFTR name. In order to
be able to populate such an option, the DHCPv6 server must be
pre-provisioned with the AFTR name.
In broadband environments, a customer profile may be managed by
Authentication, Authorization, and Accounting (AAA) servers, together
with AAA for users. The Remote Authentication Dial-In User Service
(RADIUS) protocol [RFC2865] is usually used by AAA servers to
communicate with network elements. [RADIUS-IPv6] describes a typical
broadband network scenario in which the Network Access Server (NAS)
acts as the access gateway for the users (hosts or Customer Premises
Equipment (CPE) devices) and also embeds a DHCPv6 server function
that allows it to locally handle any DHCPv6 requests issued by the
clients.
Since the DS-Lite AFTR information can be stored in AAA servers and
the client configuration is mainly provided through DHCP running
between the NAS and the requesting clients, a new RADIUS attribute is
needed to send AFTR information from the AAA server to the NAS.
This document defines a new RADIUS attribute to be used for carrying
the DS-Lite Tunnel Name, based on the equivalent DHCPv6 option
already specified in [RFC6334].
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 [RFC2119].
The terms DS-Lite Basic Bridging BroadBand element (B4) and the
DS-Lite Address Family Transition Router element (AFTR) are defined
in [RFC6333].
3. DS-Lite Configuration with RADIUS and DHCPv6
Figure 1 illustrates how the RADIUS protocol and DHCPv6 work together
to accomplish DS-Lite configuration on the B4 element when a PPP
session is used to provide connectivity to the user.
The NAS operates as a client of RADIUS and as a DHCP Server. The NAS
initially sends a RADIUS Access-Request message to the RADIUS server,
requesting authentication. Once the RADIUS server receives the
request, it validates the sending client, and if the request is
approved, the AAA server replies with an Access-Accept message
including a list of attribute-value pairs that describe the
parameters to be used for this session. This list MAY also contain
the AFTR tunnel name. When the NAS receives a DHCPv6 client request
containing the DS-Lite tunnel option, the NAS SHALL use the name
returned in the RADIUS DS-Lite-Tunnel-Name attribute to populate the
DHCPv6 OPTION_AFTR_NAME option in the DHCPv6 reply message.
B4 NAS AAA
| | Server
| | |
|----PPP LCP Config-Request------> | |
| | |
| |----Access-Request ---->|
| | |
| |<---- Access-Accept-----|
| | (DS-Lite-Tunnel-Name) |
|<-----PPP LCP Config-ACK ------- | |
| | |
| | |
|--- PPP IPv6CP Config-Request --->| |
| | |
|<----- PPP IPv6CP Config-ACK -----| |
| | |
|------- DHCPv6 Solicit -------->| |
| | |
|<-------DHCPv6 Advertisement -----| |
| (DHCPv6 OPTION_AFTR_NAME) | |
| | |
|------- DHCPv6 Request -------->| |
| | |
|<-------- DHCPv6 Reply ---------- | |
| (DHCPv6 OPTION_AFTR_NAME) | |
DHCPv6 RADIUS
Figure 1: RADIUS and DHCPv6 Message Flow for a PPP Session
Figure 2 illustrates how the RADIUS protocol and DHCPv6 work together
to accomplish DS-Lite configuration on the B4 element when an IP
session is used to provide connectivity to the user.
The only difference between this message flow and the previous one is
that in this scenario, the interaction between the NAS and the AAA/
RADIUS server is triggered by the DHCPv6 Solicit message received by
the NAS from the B4 acting as a DHCPv6 client, while in the case of a
PPP session, the trigger is the PPP Link Control Protocol (LCP)
Config-Request message received by the NAS.
B4 NAS AAA
| | Server
|------ DHCPv6 Solicit ---------> | |
| | |
| |----Access-Request ---->|
| | |
| |<---Access-Accept-------|
| | (DS-Lite-Tunnel-Name) |
| | |
|<-------DHCPv6 Advertisement------| |
| (DHCPv6 OPTION_AFTR_NAME) | |
| | |
|------- DHCPv6 Request -------->| |
| | |
| | |
|<----- DHCPv6 Reply ------------- | |
| (DHCPv6 OPTION_AFTR_NAME) | |
DHCPv6 RADIUS
Figure 2: RADIUS and DHCPv6 Message Flow for an IP Session
In the scenario depicted in Figure 2, the Access-Request packet
contains a Service-Type attribute with the value Authorize Only (17);
thus, according to [RFC5080], the Access-Request packet MUST contain
a State attribute.
After receiving the DS-Lite-Tunnel-Name attribute in the initial
Access-Accept packet, the NAS MUST store the received AFTR tunnel
name locally. When the B4 sends a DHCPv6 Renew message to request an
extension of the lifetimes for the assigned address or prefix, the
NAS does not have to initiate a new Access-Request packet towards the
AAA server to request the AFTR tunnel name. The NAS retrieves the
previously stored AFTR tunnel name and uses it in its reply.
According to [RFC3315], if the DHCPv6 server to which the DHCPv6
Renew message was sent at time T1 has not responded, the DHCPv6
client initiates a Rebind/Reply message exchange with any available
server. In this scenario, the NAS receiving the DHCPv6 Rebind
message MUST initiate a new Access-Request message towards the AAA
server. The NAS MAY include the DS-Lite-Tunnel-Name attribute in its
Access-Request message.
If the NAS does not receive the DS-Lite-Tunnel-Name attribute in the
Access-Accept message, it MAY fall back to a pre-configured default
tunnel name, if any. If the NAS does not have any pre-configured
default tunnel name or if the NAS receives an Access-Reject message,
the IPv4-over-IPv6 tunnel cannot be established; thus, the B4 element
has only IPv6 connectivity.
4. RADIUS Attribute
This section specifies the format of the new RADIUS attribute.
4.1. DS-Lite-Tunnel-Name
The DS-Lite-Tunnel-Name RADIUS attribute contains an FQDN that refers
to the AFTR to which the client is requested to establish a
connection. The NAS SHALL use the name returned in the RADIUS
DS-Lite-Tunnel-Name attribute to populate the DHCPv6 OPTION_AFTR_NAME
option [RFC6334].
This attribute MAY be used in Access-Request packets as a hint to the
RADIUS server; for example, if the NAS is pre-configured with a
default tunnel name, this name MAY be inserted in the attribute. The
RADIUS server MAY ignore the hint sent by the NAS, and it MAY assign
a different AFTR tunnel name.
If the NAS includes the DS-Lite-Tunnel-Name attribute, but the AAA
server does not recognize it, this attribute MUST be ignored by the
AAA server.
If the NAS does not receive the DS-Lite-Tunnel-Name attribute in the
Access-Accept message, it MAY fall back to a pre-configured default
tunnel name, if any. If the NAS does not have any pre-configured
default tunnel name, the tunnel cannot be established.
If the NAS is pre-provisioned with a default AFTR tunnel name and the
AFTR tunnel name received in the Access-Accept message is different
from the configured default, then the AFTR tunnel name received in
the Access-Accept message MUST be used for the session.
If the NAS cannot support the received AFTR tunnel name for any
reason, the tunnel SHOULD NOT be established.
When the Access-Request message is triggered by a DHCPv6 Rebind
message, if the AFTR tunnel name received in the Access-Accept
message is different from the currently used one for that session,
the NAS MUST force the B4 to re-establish the tunnel using the new
AFTR name received in the Access-Accept message.
If an implementation includes Change-of-Authorization (CoA) messages
[RFC5176], they could be used to modify the current established
DS-Lite tunnel. When the NAS receives a CoA Request message
containing the DS-Lite-Tunnel-Name attribute, the NAS MUST send a
Reconfigure message to a B4 to inform the B4 that the NAS has new or
updated configuration parameters and that the B4 is to initiate a
Renew/Reply or Information-Request/Reply transaction with the NAS in
order to receive the updated information.
Upon receiving an AFTR tunnel name different from the currently used
one, the B4 MUST terminate the current DS-Lite tunnel, and the B4
MUST establish a new DS-Lite tunnel with the specified AFTR.
The DS-Lite-Tunnel-Name RADIUS attribute MAY be present in
Accounting-Request records where the Acct-Status-Type is set to
Start, Stop, or Interim-Update. The DS-Lite-Tunnel-Name RADIUS
attribute MUST NOT appear more than once in a message.
A summary of the DS-Lite-Tunnel-Name RADIUS 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 | DS-Lite-Tunnel-Name (FQDN)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
144 for DS-Lite-Tunnel-Name.
Length:
This field indicates the total length in octets of this
attribute including the Type and Length fields, and the length
in octets of the DS-Lite-Tunnel-Name field.
DS-Lite-Tunnel-Name:
This field contains a single FQDN of the remote tunnel endpoint,
located at the DS-Lite AFTR.
As the DS-Lite-Tunnel-Name attribute is used to populate the DHCPv6
OPTION_AFTR_NAME option, the DS-Lite-Tunnel-Name field is formatted
as required in DHCPv6 (Section 8 of [RFC3315] -- "Representation and
Use of Domain Names"). Briefly, the format described is using a
single octet noting the length of one DNS label (limited to at most
63 octets), followed by the label contents. This repeats until all
labels in the FQDN are exhausted, including a terminating zero-length
label. Any updates to Section 8 of [RFC3315] also apply to the
encoding of this field.
The data type of the DS-Lite-Tunnel-Name RADIUS attribute is a string
with opaque encapsulation, according to Section 5 of [RFC2865].
5. Table of Attributes
The following tables provide a guide to which attributes may be found
in which kinds of packets, and in what quantity.
Access- Access- Access- Challenge Accounting # Attribute
Request Accept Reject Request
0-1 0-1 0 0 0-1 144 DS-Lite-Tunnel-Name
CoA-Request CoA-ACK CoA-NACK # Attribute
0-1 0 0 144 DS-Lite-Tunnel-Name
The following table defines the meaning of the above table entries.
0 This attribute MUST NOT be present in the packet.
0+ Zero or more instances of this attribute MAY be present in the
packet.
0-1 Zero or one instance of this attribute MAY be present in the
packet.
6. Security Considerations
This document has no additional security considerations beyond those
already identified in [RFC2865] for the RADIUS protocol and in
[RFC5176] for CoA messages.
[RFC6333] discusses security issues related to Dual-Stack Lite.
7. IANA Considerations
Per this document, IANA has allocated a new RADIUS attribute type
from the IANA registry "Radius Attribute Types" located at
http://www.iana.org/assignments/radius-types.
DS-Lite-Tunnel-Name - 144
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T.,
Perkins, C., and M. Carney, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3315,
July 2003.
[RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication
Dial In User Service (RADIUS) Implementation Issues
and Suggested Fixes", RFC 5080, December 2007.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee,
"Dual-Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) Option for
Dual-Stack Lite", RFC 6334, August 2011.
8.2. Informative References
[RADIUS-IPv6] Lourdelet, B., Dec, W., Ed., Sarikaya, B., Zorn, G.,
and D. Miles, "RADIUS attributes for IPv6 Access
Networks", Work in Progress, November 2011.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)",
RFC 5176, January 2008.
Authors' Addresses
Roberta Maglione
Telecom Italia
Via Reiss Romoli 274
Torino 10148
Italy
EMail: roberta.maglione@telecomitalia.it
Alain Durand
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089-1206
USA
EMail: adurand@juniper.net
AI ELI5
On this page
PROBLEMA Dual-Stack Lite home element (B4) needs the name of its AFTR tunnel endpoint, and DHCPv6 can deliver it, but the name may live in the provider's AAA customer profile.
MECHANISMA new RADIUS attribute, DS-Lite-Tunnel-Name (type 144), carries the AFTR's FQDN to the Network Access Server, which copies it into the DHCPv6 OPTION_AFTR_NAME option.
WHY IT MATTERSProviders can keep AFTR tunnel information in AAA profiles and still configure customers through DHCPv6. The attribute is meant for the RADIUS server and NAS, not for the B4 itself.
§1Why DS-Lite Needs RADIUS
Dual-Stack Lite (RFC 6333) offers both IPv4 and IPv6 connectivity to customers who are addressed only with an IPv6 prefix. Its key part is an IPv4-over-IPv6 tunnel. The customer's B4 element does not know whether its network supports DS-Lite, nor where the far end of the tunnel is. That far end is the AFTR (Address Family Transition Router), and its location can be given as a fully qualified domain name (FQDN).
RFC 6334 defines a DHCPv6 option the B4 uses to discover the AFTR name, but the DHCPv6 server must be pre-provisioned with that name. In broadband networks, customer profiles are often kept in AAA servers that talk RADIUS (RFC 2865) to network elements. The Network Access Server (NAS) is the access gateway and can also act as a DHCPv6 server. So a RADIUS attribute is needed to move the AFTR name from the AAA server to the NAS.
The home router needs to know which helper to call. The helper's name is written in the provider's records, so the records need a way to tell the front desk.
§2How RADIUS and DHCPv6 Work Together
The NAS is a RADIUS client and a DHCPv6 server. It sends an Access-Request to the RADIUS server, which answers with an Access-Accept holding attribute-value pairs for the session. That list MAY include the AFTR tunnel name. When the NAS gets a DHCPv6 client request containing the DS-Lite tunnel option, it SHALL use the name from the DS-Lite-Tunnel-Name attribute to fill the DHCPv6 OPTION_AFTR_NAME option in its reply.
The RFC shows two flows. With a PPP session, the NAS contacts the RADIUS server when it receives a PPP LCP Config-Request. With an IP session, the trigger is the DHCPv6 Solicit message. In the IP case the Access-Request carries a Service-Type of Authorize Only (17), so under RFC 5080 it MUST contain a State attribute.
The NAS MUST store the received name. On a DHCPv6 Renew it reuses the stored name without asking RADIUS again. On a DHCPv6 Rebind the NAS MUST send a new Access-Request, and it MAY include the attribute.
The front desk asks the office for the helper's name once, writes it down, and gives it to the router. When the router asks again later, the front desk reads from its notes.
B4NASAAA server
- DHCPv6 Solicit
- Access-Request
- Access-AcceptCarries DS-Lite-Tunnel-Name.
- DHCPv6 AdvertisementContains OPTION_AFTR_NAME.
- DHCPv6 Request
- DHCPv6 ReplyContains OPTION_AFTR_NAME.
§3The DS-Lite-Tunnel-Name Attribute
The attribute holds an FQDN naming the AFTR the client is asked to connect to. Its Type is 144. Length is the total length in octets, including the Type and Length fields. The name field is encoded as DHCPv6 requires (Section 8 of RFC 3315): a length octet for each DNS label, at most 63 octets, then the label, repeated for every label and ended by a zero-length label. The RADIUS data type is a string with opaque encapsulation.
The attribute MAY appear in Access-Request packets as a hint, for example the NAS's own default name. The server MAY ignore the hint and assign a different name. If a server does not recognize the attribute, it MUST be ignored. It MAY appear in Accounting-Request records with Acct-Status-Type Start, Stop or Interim-Update, and it MUST NOT appear more than once in a message.
The name is written as a series of short labeled pieces, like spelling a web address one part at a time, with a blank piece at the end to say it is finished.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 144 | 144 for DS-Lite-Tunnel-Name. |
LENGTH | Length | 1 byte | Total octets of the attribute, including Type and Length. | |
NAME | DS-Lite-Tunnel-Name (FQDN) | 2 bytes | FQDN of the AFTR in DHCPv6 domain-name encoding; variable length. |
§4Defaults, Changes and Failures
If the Access-Accept has no DS-Lite-Tunnel-Name, the NAS MAY fall back to a pre-configured default tunnel name. If it has none, or if it receives an Access-Reject, the tunnel cannot be established and the B4 has only IPv6 connectivity. If the received name differs from a configured default, the received name MUST be used. If the NAS cannot support the received name, the tunnel SHOULD NOT be established.
When an Access-Request triggered by a DHCPv6 Rebind returns a different name than the one in use, the NAS MUST force the B4 to re-establish the tunnel with the new name. If an implementation supports Change-of-Authorization messages (RFC 5176), a CoA Request containing the attribute makes the NAS send a Reconfigure message to the B4, which then does a Renew/Reply or Information-Request/Reply to get the update. A B4 that receives a different AFTR name MUST terminate its current tunnel and set up a new one.
If the office gives no name, the front desk may use a backup name. If the name changes, the router hangs up on the old helper and calls the new one.
§5Attribute Table, IANA and Security
The attribute table allows zero or one instance (0-1) in Access-Request, Access-Accept, Accounting-Request and CoA-Request, and none in Access-Reject, Access-Challenge, CoA-ACK or CoA-NACK. IANA allocated type 144 for DS-Lite-Tunnel-Name in the Radius Attribute Types registry.
There are no additional security considerations beyond those of RFC 2865 for RADIUS and RFC 5176 for CoA messages. RFC 6333 discusses security issues for Dual-Stack Lite itself.
The attribute gets its own number, 144, and the rules for guarding it are the ones RADIUS already has.
§6References
[RFC2865]RFC 2865Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000.June 2000[RFC3315]RFC 3315Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.July 2003[RFC5080]RFC 5080Nelson, D. and A. DeKok, "Common Remote Authentication Dial In User Service (RADIUS) Implementation Issues and Suggested Fixes", RFC 5080, December 2007.December 2007[RFC6333]RFC 6333Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, August 2011.August 2011[RFC6334]RFC 6334Hankins, D. and T. Mrugalski, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite", RFC 6334, August 2011.August 2011[RFC5176]RFC 5176Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B. Aboba, "Dynamic Authorization Extensions to Remote Authentication Dial In User Service (RADIUS)", RFC 5176, January 2008.January 2008