RFC 6930

RADIUS Attribute for IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)

📅 published April 2013, from ietf

RFC 6930 🎀 RADIUS Attribute for IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)

okay bestie, the title block first 💅 this doc is a Standards Track RFC (ISSN 2070-1721), dated April 2013, and it's by D. Guo, S. Jiang (Ed.), R. Despres, and R. Maglione. Guo and Jiang are at Huawei Technologies Co., Ltd, Despres is at RD-IPtech, and Maglione is at Cisco Systems. The header doesn't list anything it obsoletes or updates 🌸

Abstract ✨

okay so 6rd (IPv6 Rapid Deployment on IPv4 Infrastructures) gives you IPv4 and IPv6 connectivity at the same time during the IPv4/IPv6 coexistence period 🦋 there's already a DHCP 6rd option for setting up the 6rd Customer Edge (CE), but the config info is often stored in AAA servers, while the user's config mostly gets fetched from a Broadband Network Gateway (BNG) over DHCP. so this doc defines a RADIUS attribute that carries the 6rd config from the AAA server to the BNGs. it's giving connecting the dots 🔥

Status of This Memo 📜

this is an Internet Standards Track document 🧚

it's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community. it got public review and was approved for publication by the Internet Engineering Steering Group (IESG). more info on Internet Standards is in Section 2 of RFC 5741.

info about the current status, any errata, and how to give feedback lives at http://www.rfc-editor.org/info/rfc6930 💜

Copyright Notice ©️

this doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stand on the publication date. please actually read those, they spell out your rights and restrictions for this doc 🙈

if you extract Code Components from this document, they must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 💖

Table of Contents 🗺️

1. Introduction ....................................................3
2. Terminology .....................................................3
3. IPv6 6rd Configuration with RADIUS ..............................4
4. Attributes ......................................................6
   4.1. IPv6-6rd-Configuration Attribute ...........................6
   4.2. Table of Attributes ........................................9
5. Diameter Considerations .........................................9
6. Security Considerations .........................................9
7. IANA Considerations ............................................10
8. Acknowledgments ................................................10
9. References .....................................................10
   9.1. Normative References ......................................10
   9.2. Informative References ....................................11

1. Introduction 🌈

okay so providers are starting to roll out IPv6 and think about transitioning to it 🚀 6rd [RFC5969] gives you IPv4 and IPv6 connectivity at once during coexistence. it's used to deliver IPv6 service over legacy IPv4-only infrastructure, and it uses the Dynamic Host Configuration Protocol (DHCP) [RFC2131]. the 6rd CE uses the DHCP 6rd option [RFC5969] to discover a 6rd Border Relay and to configure an IPv6 prefix and address ✨

in lots of networks, user config is managed by Authentication, Authorization, and Accounting (AAA) servers. the Remote Authentication Dial-In User Service (RADIUS) protocol [RFC2865] is usually what AAA servers use to talk to 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, so they can handle any DHCP requests from hosts locally 💅

the 6rd config is stored in AAA servers, but user config mostly flows over DHCP between BNGs and hosts/CEs. so we need new RADIUS attributes to pass the info from AAA servers to BNGs. main character energy for RADIUS 👑

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]. "MAC" stands for Media Access Control 🦋

3. IPv6 6rd Configuration with RADIUS 🎀

okay this section is the choreography 💃 Figure 1 shows how DHCP and RADIUS work together to give the 6rd CE its 6rd config 🧚

      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
                 When Combined with RADIUS Authentication

the BNG is a RADIUS client and a DHCP server, bestie 🫶 first, the 6rd CE MAY start with a DHCPDISCOVER message that includes a Parameter Request option (55) [RFC2132] with the 6rd option [RFC5969]. when the BNG gets that DHCPDISCOVER, it SHOULD start a RADIUS Access-Request message to the RADIUS server. in that message:

the User-Name attribute (1) SHOULD be filled by the 6rd CE MAC address, and
the User-Password attribute (2) SHOULD be filled by the shared 6rd password that has been preconfigured on the DHCP server.

the BNG asks for authentication, as defined in [RFC2865], with the IPv6-6rd-Configuration attribute (Section 4.1) in the desired attribute list 🔐 if the AAA server approves the authentication request, an Access-Accept message MUST be acknowledged with the IPv6-6rd-Configuration attribute. then the BNG SHOULD reply to the 6rd CE with a DHCPOFFER message that contains a DHCP 6rd option ✨ the recommended format of the MAC address is the one defined in Calling-Station-Id ([RFC3580], Section 3.20) without the SSID (Service Set Identifier) portion 💖

Figure 2 is a different scenario, the later re-authorization 🔄 here the authorization isn't coupled with authentication. the 6rd-relevant authorization happens 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
                 When Decoupled from RADIUS Authentication

in this scenario, the Access-Request packet SHOULD contain a Service-Type attribute (6) with the value Authorize Only (17). so, according to [RFC5080], the Access-Request packet MUST contain a State attribute that it gets from the previous authentication process 🧠

in both of the scenarios above, Message-Authenticator (type 80) [RFC2865] SHOULD be used to protect both the Access-Request and Access-Accept messages 🛡️

once the BNG gets the IPv6-6rd-Configuration attribute in the initial Access-Accept, it SHOULD store the received 6rd config parameters locally. that way, when the 6rd CE sends a DHCP Request message to extend the lifetime of its assigned address, the BNG doesn't have to start a new Access-Request to the AAA server for the 6rd config. it could pull the stored parameters and use them in its reply 🍓

if the BNG doesn't get the IPv6-6rd-Configuration attribute in the Access-Accept, it MAY fall back to a preconfigured default 6rd config, if there is one. if the BNG has no preconfigured default 6rd config, or if it gets an Access-Reject, the tunnel cannot be established 💀

as specified in [RFC2131], Section 4.4.5 ("Reacquisition and expiration"), if the DHCP server that got the DHCP Request message sent at time T1 hasn't responded by time T2 (typically 0.375*duration_of_lease after T1), the 6rd CE (the DHCP client) SHOULD enter the REBINDING state and try to contact any server 🦋

in that situation, the secondary BNG that receives the new DHCP message MUST start a new Access-Request to the AAA server. the secondary BNG MAY include the IPv6-6rd-Configuration attribute in its Access-Request 🫶

4. Attributes ✨

this section defines the IPv6-6rd-Configuration attribute, which is used in both of the scenarios above 💜 the attribute design follows [RFC6158] and refers to [RFC6929] 🌈

4.1. IPv6-6rd-Configuration Attribute 🎀

okay so bestie, this part is where the magic happens ✨. The spec says that multiple IPv4 addresses have to be tied to one IPv6 prefix 💅. RADIUS doesn't have a recommended way to group a bunch of attributes together yet, so the design below is kinda the best compromise anyone could come up with 🫶. Here's how the IPv6-6rd-Configuration attribute is laid out 🦋:

    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

The Type is 173 🌈.

Length

The Length is 28 + n*6, which is the whole attribute length in octets 📏. Here n is the number of BR IPv4 addresses, and the minimum for n is 1 🧚.

SubType1

SubType1 is 1 🍓. It's the SubType number for the IPv4 Mask Length suboption.

SubLen1

SubLen1 is 6 💖. That's the length of the IPv4 Mask Length suboption.

IPv4MaskLen

This is the number of high-order bits that are identical across all CE IPv4 addresses inside a given 6rd domain 👑. It can be any value from 0 to 32, and anything bigger than 32 is invalid 🙈. Since [RFC6158], Appendix A.2.1, has forbidden 8-bit fields, a 32-bit field is used here 💅.

SubType2

SubType2 is 2 ✨. It's the SubType number for the 6rd prefix suboption.

SubLen2

SubLen2 is 20 🦋. That's the length of the 6rd prefix suboption.

Reserved

This is set to all 0 for now, and it's reserved for future use 🫶. To stay 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

This is the IPv6 prefix length of the Service Provider's 6rd IPv6 prefix, counted in bits 🌸. The 6rdPrefixLen MUST be less than or equal to 128 💜.

6rdPrefix

This is the Service Provider's 6rd IPv6 prefix, shown as a 16-octet IPv6 address 🌈. The bits after the 6rdPrefixlen number of bits in the prefix SHOULD be set to zero ⭐.

SubType3

SubType3 is 3 💅. It's the SubType number for the 6rd Border Relay IPv4 address suboption.

SubLen3

SubLen3 is 6 🎀. That's the length of the 6rd Border Relay IPv4 address suboption.

6rdBRIPv4Address

This is one or more IPv4 addresses of the 6rd Border Relay(s) for a given 6rd domain 🦋. The maximum RADIUS attribute length of 255 octets gives us a limit of 37 IPv4 addresses 😭.

Since the subtypes have values, they can show up in any order 🧚. If multiple 6rdBRIPv4Address (subtype 3) entries appear, they are RECOMMENDED to be placed together 🫶.

The IPv6-6rd-Configuration attribute is normally used in Access-Accept messages 👑. It MAY also be used in Access-Request packets as a hint for the RADIUS server 🌸. For example, if the BNG is preconfigured with a default 6rd configuration, those parameters MAY be inserted into the attribute 💖. The RADIUS server MAY ignore the hint from the BNG, and it MAY assign different 6rd parameters 💅.

If the BNG includes the IPv6-6rd-Configuration attribute but the AAA server doesn't recognize it, the AAA server MUST ignore this attribute 🙈.

If the BNG doesn't receive the IPv6-6rd-Configuration attribute in the Access-Accept, it MAY fall back to a preconfigured default 6rd configuration, if there is one 🍓. If the BNG doesn't have any preconfigured 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 the Access-Accept is different from that default, then the 6rd configuration received in the Access-Accept message MUST be used for the session 🔥.

If the BNG can't support the received 6rd configuration for any reason, the tunnel SHOULD NOT be established 😭.

4.2. Table of Attributes 🌈

4.2. Table of Attributes

This table adds to the one in [RFC2865], Section 5.44, and it's a handy guide to how many IPv6-6rd-Configuration attributes can show up in each kind of packet 💅.

Request Accept Reject Challenge Accounting  #  Attribute
                                 Request
 0-1     0-1     0      0         0-1      173  IPv6-6rd-
                                                Configuration
 0-1     0-1     0      0         0-1      1    User-Name
 0-1     0       0      0         0-1      2    User-Password
 0-1     0-1     0      0         0-1      6    Service-Type
 0-1     0-1     0-1    0-1       0-1      80   Message-Authenticator

Here's the key for the 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 works with either RADIUS or Diameter [RFC6733] 🫶. Since the attribute in this document comes from the standard RADIUS type space, Diameter entities don't need any special handling 🧚.

6. Security Considerations 🔥

In 6rd scenarios, both the CE and the BNG live inside a provider network, which can be treated as a closed network and a lower-threat environment 🌸. A similar consideration applies to the RADIUS message exchange between the BNG and the AAA server 💜.

In 6rd scenarios, RADIUS runs over IPv4 😭. Known security vulnerabilities of the RADIUS protocol are discussed in [RFC2607], [RFC2865], and [RFC2869] 💀. Using IPsec [RFC4301] to provide security when RADIUS is carried over IPv6 is discussed in [RFC3162] 🙈.

To get unauthorized 6rd configuration information, a malicious user may use MAC address spoofing and/or a dictionary attack on the shared 6rd password that's been preconfigured on the DHCP server 🚨. The relevant security issues are covered in Section 12 of [RFC5969] 👑.

Security issues that may arise specifically between the 6rd CE and the BNG are discussed in [RFC5969] 🎀. Furthermore, generic DHCP security mechanisms can be applied to DHCP intercommunication between the 6rd CE and the BNG ✨.

Security considerations for the Diameter protocol are discussed in [RFC6733] 💅.

7. IANA Considerations 🌈

Per this document, IANA has assigned one new RADIUS Attribute Type in the "Radius Types" registry (currently located at http://www.iana.org/assignments/radius-types) for the following attribute 🦋:

   IPv6-6rd-Configuration (173)

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 the SOFTWIRE WG, RADEXT WG, AAA Doctors, and Security Directorate 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]  Droms, R., "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 A. DeKok, "Common Remote Authentication
           Dial In User Service (RADIUS) Implementation Issues and
           Suggested Fixes", RFC 5080, December 2007.

[RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
           Infrastructures (6rd) -- Protocol Specification", RFC
           5969, August 2010.

[RFC6158]  DeKok, A., Ed., and G. Weber, "RADIUS Design Guidelines",
           BCP 158, RFC 6158, March 2011.

[RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
           Ed., "Diameter Base Protocol", RFC 6733, October 2012.

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.

[RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
           "IEEE 802.1X Remote Authentication Dial In User Service
           (RADIUS) Usage Guidelines", RFC 3580, September 2003.

[RFC6929]  DeKok, A. and A. Lior, "Remote Authentication Dial-In User
           Service (RADIUS) Protocol Extensions", RFC 6929, April
           2013.

Authors' 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
Cisco Systems
181 Bay Street
Toronto, ON
M5J 2T3
Canada

EMail: robmgl@cisco.com

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