Network Working Group                                       Dayong Guo
Internet Draft                                    Sheng Jiang (Editor)
Intended status: Standards Track          Huawei Technologies Co., Ltd
Expires: April 11, 2013                                     R. Despres
                                                             RD-IPtech
                                                           R. Maglione
                                                        Telecom Italia
                                                      October 10, 2012



                        RADIUS Attribute for 6rd

              draft-ietf-softwire-6rd-radius-attrib-07.txt


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Abstract

   IPv6 Rapid Deployment (6rd) is one of the most popular methods to
   provide both IPv4 and IPv6 connectivity services simultaneously
   during the IPv4/IPv6 co-existing period. The Dynamic Host
   Configuration Protocol (DHCP) 6rd option has been defined to
   configure 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 from Broadband Network Gateway (BNG) through DHCP protocol.
   This document defines a Remote Authentication Dial In User Service
   (RADIUS) attribute that carries 6rd configuration information from
   AAA server to BNG.



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 ..................................... 8
   6. Security Considerations ..................................... 9
   7. IANA Considerations ......................................... 9
   8. Acknowledgments ............................................. 9
   9. References .................................................. 9
      9.1. Normative References ................................... 9
      9.2. Informative References ................................ 10















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1. Introduction

   Recently providers start to deploy IPv6 and consider how to transit
   to IPv6. IPv6 Rapid Deployment (6rd) [RFC5969] is one of the most
   popular methods to provide both IPv4 and IPv6 connectivity services
   simultaneously during the IPv4/IPv6 co-existing period. 6rd is used
   to provide IPv6 connectivity service through legacy IPv4-only
   infrastructure. 6rd adopts Dynamic Host Configuration Protocol (DHCP)
   [RFC2131] as auto-configuring protocol. The 6rd Customer Edge (CE)
   uses the DHCP 6rd option [RFC5969] to discover 6rd border relay and
   to configure IPv6 prefix and address.

   In many networks, user configuration information may be managed by
   AAA (Authentication, Authorization, and Accounting) servers. Current
   AAA servers communicate using the Remote Authentication Dial In User
   Service (RADIUS) [RFC2865] protocol. In a fixed line broadband
   network, the Broadband Network Gateways (BNGs) act as the access
   gateway of users. The BNGs are assumed to embed a DHCP server
   function that allows them to locally handle any DHCP requests issued
   by hosts.

   Since the 6rd configuration information is stored in AAA servers and
   user configuration is mainly through DHCP protocol 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 CE and 6rd Border Relay are defined in [RFC5969].

3. IPv6 6rd Configuration with RADIUS

   The below 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)        |                             |
         |--------DHCPREQUEST------>|                             |
         |(Parameter Request w/ 6rd option)                       |
         |<--------DHCPACK----------|                             |
         |      (6rd option)        |                             |
         |                          |                             |
                   DHCP                         RADIUS
                Figure 1: the cooperation between DHCP and RADIUS

   BNGs act as a client of RADIUS and as a DHCP server for DHCP
   protocol. First, a BNG receives a DHCPDISCOVER from the 6rd CE. It
   initiates the BNG to request correspondent user authorization
   relevant from an AAA server using RADIUS protocol. A 6rd
   configuration request may also be sent in the same message. If the
   user authorization is approved by the AAA server, an Access-Accept
   message is acknowledged with the IPv6-6rd-Configuration Attribute,
   defined in the next Section. After the BNG responds to the user with
   an Advertise message, the user requests for a DHCP 6rd Option by
   carrying a Parameter Request option (55) [RFC2132]. Then, the BNG can
   reply the user using the DHCP protocol.

   In the abovementioned scenario, the Access-Request packet contains a
   Service-Type attribute with the value Call-Check (10).

   Figure 2 describes another scenario, in which the authorization
   operation is not coupled with DHCP. In the authorization stage, the
   BNG obtains the 6rd configuration information from the AAA server
   through the RADIUS protocol. When the user requests the 6rd Option
   using a Parameter Request option, the BNG replies with a 6rd option
   in DHCPACK.










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      6rd CE                       BNG                       AAA Server
         |                          |                             |
         |                          |--Access-Request(6rd Attr)-->|
         |                          |                             |
         |                          |<--Access-Accept(6rd Attr)---|
         |                          |                             |
         |--------DHCPREQUEST------>|                             |
         |(Parameter Request w/ 6rd option)                       |
         |<---------DHCPACK---------|                             |
         |      (6rd option)        |                             |
         |                          |                             |
                   DHCP                         RADIUS
                Figure 2: the cooperation between DHCP and RADIUS

   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 use them in
   its reply.

   If the DHCP server to which the DHCP Request message was sent at time
   T1 has not responded, the DHCP client enters the REBINDING state and
   attempts to contact any server. In this scenario the BNG receiving
   the DHCP message MUST initiate a new Access-Request towards the AAA
   server. The BNG MAY include the IPv6-6rd-Configuration Attribute in
   its Access-Request. 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 or if the BNG
   receives an Access-Reject, the tunnel cannot be established.

4. Attributes

   This section defines IPv6-6rd-Configuration Attribute which is used
   in the 6rd scenario. The attribute design follows [RFC6158].

4.1. IPv6-6rd-Configuration Attribute

   The IPv6-6rd-Configuration Attribute is structured as follows (The
   specification requires that multiple IPv4 addresses are associated
   strongly with one IPv6 prefix. Given that RADIUS currently has no
   recommended way of grouping multiple attributes, the below design
   appears to be a reasonable compromise.):



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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     |    SubType    |    SubLen     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          IPv4MaskLen                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    SubType    |    SubLen     |  Reserved     |  6rdPrefixLen |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                           6rdPrefix                           +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   SubType     |    SubLen     |        6rdBRIPv4Address       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        6rdBRIPv4Address       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type

         TBD

       Length

         28 + n*6 (the length of the entire attribute in octets; n
         stands the number of BR IPv4 addresses, minimum n is 1).

       SubType

         1 (SubType number, for the IPv4 Mask Length suboption)

       SubLen

         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.

       SubType



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         2 (SubType number, for the 6rd prefix suboption)

       SubLen

         20 (the length of the 6rd prefix suboption)

       Reserved

         Set to be all 0 for now. Reserved for the future use. To be
         compatible with other IPv6 prefix attributes in the RADIUS
         Protocol.

       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.

       SubType

         3 (SubType number, for the 6rd Border Relay IPv4 address
         suboption)

       SubLen

         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 58 IPv4 addresses.

   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 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



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   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 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 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     0-1     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.
   1     Exactly one instance of this attribute MUST be present in
         packet.

5. Diameter Considerations

   This attribute is usable within either RADIUS or Diameter [RFC3588].
   Since the Attributes defined in this document will be allocated from
   the standard RADIUS type space, no special handling is required by
   Diameter entities.



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6. Security Considerations

   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 the Diameter protocol are discussed in
   [RFC3588].

7. IANA Considerations

   This document requires 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
   space using the "IETF Review" policy [RFC5226].

8. Acknowledgments

   The authors would like to thank Alan DeKok, Yong Cui and other
   members of Softwire WG 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.


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   [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.,
             Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

   [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
             Internet Protocol", RFC 4301, December 2005.

   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
             IANA Considerations Section in RFCs", RFC 5226, May 2008.

   [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.

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.

























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   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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