Network Working Group Dayong Guo
Internet Draft Sheng Jiang (Editor)
Intended status: Standards Track Huawei Technologies Co., Ltd
Expires: June 20, 2013 R. Despres
RD-IPtech
R. Maglione
Telecom Italia
December 19, 2012
RADIUS Attribute for 6rd
draft-ietf-softwire-6rd-radius-attrib-09.txt
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Abstract
IPv6 Rapid Deployment (6rd) provides both IPv4 and IPv6 connectivity
services simultaneously during the IPv4/IPv6 co-existence period. The
Dynamic Host Configuration Protocol (DHCP) 6rd option has been
defined to configure the 6rd Customer Edge (CE). However, in many
networks, the configuration information may be stored in
Authentication Authorization and Accounting (AAA) servers while user
configuration is mainly acquired from a Broadband Network Gateway
(BNG) through the DHCP protocol. This document defines a Remote
Authentication Dial In User Service (RADIUS) attribute that carries
6rd configuration information from the AAA server to BNGs.
Table of Contents
1. Introduction ................................................ 3
2. Terminology ................................................. 3
3. IPv6 6rd Configuration with RADIUS .......................... 3
4. Attributes .................................................. 5
4.1. IPv6-6rd-Configuration Attribute ....................... 5
4.2. Table of attributes .................................... 8
5. Diameter Considerations ..................................... 9
6. Security Considerations ..................................... 9
7. IANA Considerations ......................................... 9
8. Acknowledgments ............................................ 10
9. References ................................................. 10
9.1. Normative References .................................. 10
9.2. Informative References ................................ 11
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1. Introduction
Recently providers have started to deploy IPv6 and to consider
transition to IPv6. IPv6 Rapid Deployment (6rd) [RFC5969] provides
both IPv4 and IPv6 connectivity services simultaneously during the
IPv4/IPv6 co-existence period. 6rd is used to provide IPv6
connectivity service through legacy IPv4-only infrastructure. 6rd
uses Dynamic Host Configuration Protocol (DHCP) [RFC2131] and the 6rd
Customer Edge (CE) uses the DHCP 6rd option [RFC5969] to discover a
6rd border relay and to configure IPv6 prefix and address.
In many networks, user configuration information is managed by AAA
(Authentication, Authorization, and Accounting) servers. The Remote
Authentication Dial-In User Service (RADIUS) protocol [RFC2865] is
usually used by AAA servers to communicate with network elements. In
a fixed line broadband network, the Broadband Network Gateways (BNGs)
act as the access gateway for users. The BNGs are assumed to embed a
DHCP server function that allows them to handle locally any DHCP
requests issued by hosts.
Since the 6rd configuration information is stored in AAA servers and
user configuration is mainly through DHCP between BNGs and hosts/CEs,
new RADIUS attributes are needed to propagate the information from
AAA servers to BNGs.
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 6rd Customer Edge (6rd CE) and 6rd Border Relay (BR) are
defined in [RFC5969].
3. IPv6 6rd Configuration with RADIUS
Figure 1 illustrates how the RADIUS protocol and DHCP cooperate to
provide 6rd CE with 6rd configuration information.
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6rd CE BNG AAA Server
| | |
|-------DHCPDISCOVER------>| |
|(Parameter Request w/ 6rd option) |
| |--Access-Request(6rd Attr)-->|
| | |
| |<--Access-Accept(6rd Attr)---|
|<-------DHCPOFFER---------| |
| (6rd option) | |
| | |
DHCP RADIUS
Figure 1: the cooperation between DHCP and RADIUS
combining with RADIUS authentication
The BNG acts as a client of RADIUS and as a DHCP server. First, the
6rd CE initiates a DHCPDISCOVER message that includes a Parameter
Request option (55) [RFC2132] with the 6rd option [RFC5969]. When the
BNG receives the DHCPDISCOVER, it initiates a RADIUS Access-Request
message, in which the User-Name attribute is filled by the 6rd CE MAC
address, to the RADIUS server and the User-password attribute is
filled by the shared 6rd password that has been preconfigured on the
DHCP server, requesting authentication as defined in [RFC2865] with
IPv6-6rd-Configuration attribute, defined in the next Section, in the
desired attribute list. If the authentication request is approved by
the AAA server, an Access-Accept message is acknowledged with the
IPv6-6rd-Configuration Attribute. Then, the BNG responds to the 6rd
CE with a DHCPOFFER message, which contains a DHCP 6rd option.
Figure 2 describes another scenario - later re-authorize - in which
the authorization operation is not coupled with authentication.
Authorization relevant to 6rd is done independently after the
authentication process.
6rd CE BNG AAA Server
| | |
|--------DHCPREQUEST------>| |
|(Parameter Request w/ 6rd option) |
| |--Access-Request(6rd Attr)-->|
| | |
| |<--Access-Accept(6rd Attr)---|
| | |
|<---------DHCPACK---------| |
| (6rd option) | |
| | |
DHCP RADIUS
Figure 2: the cooperation between DHCP and RADIUS
decoupled with RADIUS authentication
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In this scenario, 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
that obtains from the previous authentication process.
In both above-mentioned scenarios, Message-authenticator (type 80)
[RFC2865] SHOULD be used to protect both Access-Request and Access-
Accept messages.
After receiving the IPv6-6rd-Configuration Attribute in the initial
Access-Accept, the BNG MUST store the received 6rd configuration
parameters locally. When the 6rd CE sends a DHCP Request message to
request an extension of the lifetime for the assigned address, the
BNG does not have to initiate a new Access-Request towards the AAA
server to request the 6rd configuration parameters. The BNG retrieves
the previously stored 6rd configuration parameters and uses them in
its reply.
If the BNG does not receive the IPv6-6rd-Configuration Attribute in
the Access-Accept it MAY fall back to a pre-configured default 6rd
configuration, if any. If the BNG does not have any pre-configured
default 6rd configuration or if the BNG receives an Access-Reject,
the tunnel cannot be established.
As specified in [RFC2131], section 4.4.5, "Reacquisition and
expiration", if the DHCP server to which the DHCP Request message was
sent at time T1 has not responded by time T2 (typically
0.375*duration_of_lease after T1), the 6rd CE (the DHCP client)
enters the REBINDING state and attempts to contact any server. In
this situation, the secondary BNG receiving the new DHCP message MUST
initiate a new Access-Request towards the AAA server. The secondary
BNG MAY include the IPv6-6rd-Configuration Attribute in its Access-
Request.
4. Attributes
This section defines IPv6-6rd-Configuration Attribute which is used
in the both abovementioned scenarios. The attribute design follows
[RFC6158].
4.1. IPv6-6rd-Configuration Attribute
The specification requires that multiple IPv4 addresses are
associated with one IPv6 prefix. Given that RADIUS currently has no
recommended way of grouping multiple attributes, the design below
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appears to be a reasonable compromise. The IPv6-6rd-Configuration
Attribute is structured as follows:
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 | SubType1 | SubLen1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4MaskLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubType2 | SubLen2 | Reserved | 6rdPrefixLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ 6rdPrefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubType3 | SubLen3 | 6rdBRIPv4Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6rdBRIPv4Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
TBD
Length
28 + n*6 (the length of the entire attribute in octets; n
stands for the number of BR IPv4 addresses, minimum n is 1).
SubType1
1 (SubType number, for the IPv4 Mask Length suboption)
SubLen1
6 (the length of the IPv4 Mask Length suboption)
IPv4MaskLen
The number of high-order bits that are identical across all CE
IPv4 addresses within a given 6rd domain. This may be any value
between 0 and 32. Any value greater than 32 is invalid. Since
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[RFC6158] Section A.2.1 has forbidden 8-bit fields, a 32-bit
field is used here.
SubType2
2 (SubType number, for the 6rd prefix suboption)
SubLen2
20 (the length of the 6rd prefix suboption)
Reserved
Set to be all 0 for now. Reserved for future use. To be
compatible with other IPv6 prefix attributes in the RADIUS
Protocol. The bits MUST be set to zero by the sender and MUST
be ignored by the receiver.
6rdPrefixLen
The IPv6 Prefix length of the Service Provider's 6rd IPv6
prefix in number of bits. The 6rdPrefixLen MUST be less than or
equal to 128.
6rdPrefix
The Service Provider's 6rd IPv6 prefix represented as a 16
octet IPv6 address. The bits after the 6rdPrefixlen number of
bits in the prefix SHOULD be set to zero.
SubType3
3 (SubType number, for the 6rd Border Relay IPv4 address
suboption)
SubLen3
6 (the length of the 6rd Border Relay IPv4 address suboption)
6rdBRIPv4Address
One or more IPv4 addresses of the 6rd Border Relay(s) for a
given 6rd domain. The maximum RADIUS Attribute length of 255
octets results in a limit of 37 IPv4 addresses.
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Since the subtypes have values, they can appear in any order. If
multiple 6rdBRIPv4Address (subtype 3) appear, they are RECOMMENDED to
be placed together.
The IPv6-6rd-Configuration Attribute is normally used in the
Access-Accept messages. It MAY be used in Access-Request packets as a
hint to the RADIUS server; for example if the BNG is pre-configured
with a default 6rd configuration, these parameters MAY be inserted in
the attribute. The RADIUS server MAY ignore the hint sent by the BNG
and it MAY assign different 6rd parameters.
If the BNG includes the IPv6-6rd-Configuration Attribute, but the AAA
server does not recognize it, this attribute MUST be ignored by the
AAA Server.
If the BNG does not receive the IPv6-6rd-Configuration Attribute in
the Access-Accept it MAY fallback to a pre-configured default 6rd
configuration, if any. If the BNG does not have any pre-configured
default 6rd configuration, the 6rd tunnel cannot be established.
If the BNG is pre-provisioned with a default 6rd configuration and
the 6rd configuration received in Access-Accept is different from the
configured default, then the 6rd configuration received in the
Access-Accept message MUST be used for the session.
If the BNG cannot support the received 6rd configuration for any
reason, the tunnel SHOULD NOT be established.
4.2. Table of attributes
The following table adds to the one in [RFC2865], Section 5.44,
providing a guide to the quantity of IPv6-6rd-Configuration
attributes that may be found in each kind of packet.
Request Accept Reject Challenge Accounting # Attribute
Request
0-1 0-1 0 0 0-1 TBD IPv6-6rd-
Configuration
The following table defines the meanings of the above table entries.
0 This attribute MUST NOT be present in packet.
0+ Zero or more instances of this attribute MAY be present in
packet.
0-1 Zero or one instance of this attribute MAY be present in
packet.
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1 Exactly one instance of this attribute MUST be present in
packet.
5. Diameter Considerations
This attribute is usable within either RADIUS or Diameter [RFC6733].
Since the Attributes defined in this document will be allocated from
the standard RADIUS type space, no special handling is required by
Diameter entities.
6. Security Considerations
In 6rd scenarios, both CE and BNG are within a provider network,
which can be considered as a closed network and a lower security
threat environment. A similar consideration can be applied to the
RADIUS message exchange between BNG and the AAA server.
In 6rd scenarios, the RADIUS protocol is run over IPv4. Known
security vulnerabilities of the RADIUS protocol are discussed in
[RFC2607], [RFC2865], and [RFC2869]. Use of IPsec [RFC4301] for
providing security when RADIUS is carried in IPv6 is discussed in
[RFC3162].
Security considerations for 6rd specific between 6rd CE and BNG are
discussed in [RFC5969]. Furthermore, generic DHCP security mechanisms
can be applied DHCP intercommunication between 6rd CE and BNG.
Security considerations for the Diameter protocol are discussed in
[RFC6733].
7. IANA Considerations
This document requests the assignment of one new RADIUS Attribute
Types in the "RADIUS Types" registry (currently located at
http://www.iana.org/assignments/radius-types for the following
attributes:
o IPv6-6rd-Configuration
IANA should allocate the number from the standard RADIUS Attributes
range (values 1-191). The RFC Editor should use the assigned value
to replace "TBD" in Sections 4.1 and 4.2, and should remove this
paragraph.
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8. Acknowledgments
The authors would like to thank Alan DeKok, Yong Cui, Leaf Yeh, Sean
Turner, Joseph Salowey, Glen Zorn, Dave Nelson, Bernard Aboba, Benoit
Claise, Barry Lieba, Stephen Farrell, Adrian Farrel, Ralph Droms and
other members of Softwire WG, RADIUSExt WG, AAA-Doctors and Secdir
for valuable comments.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3162] Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC
3162, August 2001.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC5080] Nelson, D. and DeKok A., "Common Remote Authentication Dial
In User Service (RADIUS) Implementation Issues and
Suggested Fixes", RFC 5080, December 2007.
[RFC5969] Townsley, M. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC5969,
August 2010.
[RFC6158] DeKok, A. and G. Weber, "RADIUS Design Guidelines", RFC
6158, March 2011.
[RFC6733] V. Fajardo, Ed., J. Arkko, J. Loughney, G. Zorn, Ed.,
"Diameter Base Protocol", RFC 6733, October 2012.
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9.2. Informative References
[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.
[RFC2869] Rigney, C., Willats, W., and P. Calhoun, "RADIUS
Extensions", RFC 2869, June 2000.
Author's Addresses
Dayong Guo
Huawei Technologies Co., Ltd
Q14 Huawei Campus, 156 BeiQi Road,
ZhongGuan Cun, Hai-Dian District, Beijing 100095
P.R. China
Email: guoseu@huawei.com
Sheng Jiang (Editor)
Huawei Technologies Co., Ltd
Q14 Huawei Campus, 156 BeiQi Road,
ZhongGuan Cun, Hai-Dian District, Beijing 100095
P.R. China
Email: jiangsheng@huawei.com
Remi Despres
RD-IPtech
3 rue du President Wilson
Levallois,
France
Email: despres.remi@laposte.net
Roberta Maglione
Telecom Italia
Via Reiss Romoli 274
Torino 10148
Italy
Email: roberta.maglione@telecomitalia.it
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