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Attachment Individual Identifier (AII) Types for Aggregation

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 5003.
Authors Florin Balus , Luca Martini , Chris Metz , Jeff Sugimoto
Last updated 2015-10-14 (Latest revision 2007-02-07)
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state (None)
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IESG IESG state RFC 5003 (Proposed Standard)
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Mark Townsley
Send notices to (None)
Network Working Group                                         Chris Metz
Internet Draft                                              Luca Martini
Expiration Date: August 2007                          Cisco Systems Inc.

Jeff Sugimoto                                               Florin Balus
Nortel Networks                                                  Alcatel

                                                           February 2007

                       AII Types for Aggregation


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   The signaling protocols used to establish point-to-point pseudowires
   include type-length-value (TLV) fields that identify pseudowire
   endpoints called attachment individual identifiers (AII). This
   document defines AII structures in the form of new AII type-length-
   value fields that support AII aggregation for improved scalability

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   and VPN autodiscovery. It is envisioned that this would be useful in
   large inter-domain virtual private wire service networks where
   pseudowires are established between selected local and remote PE
   nodes based on customer need.

Table of Contents

    1        Specification of Requirements  ........................   2
    2        Introduction  .........................................   2
    3        Structure for the New AII Type  .......................   4
    3.1      AII Type 1  ...........................................   4
    3.2      AII Type 2  ...........................................   4
    4        IANA Considerations  ..................................   5
    5        Security Considerations  ..............................   6
    6        Acknowledgments  ......................................   6
    7        Full Copyright Statement  .............................   6
    8        Intellectual Property Statement  ......................   6
    9        Normative References  .................................   7
   10        Author Information  ...................................   7

1. Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119.

2. Introduction

   [RFC4447] defines the signaling mechanisms for establishing point-
   to-point pseudowires (PWs) between two provider edge (PE) nodes. When
   a PW is set up, the LDP signaling messages include a forwarding
   equivalence class (FEC) element containing information about the PW
   type and an endpoint identifier used in the selection of the PW
   forwarder that binds the PW to the attachment circuit at each end.

   There are two types of FEC elements defined for this purpose: PWid
   FEC (type 128) and the Generalized ID (GID) FEC (type 129). The PWid
   FEC element includes a fixed-length 32 bit value called the PWid that
   serves as an endpoint identifier. The same PWid value must be
   configured on the local and remote PE prior to PW setup.

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   The GID FEC element includes TLV fields for attachment individual
   identifiers (AII) that, in conjunction with an attachment group
   identifier (AGI), serve as PW endpoint identifiers. The endpoint
   identifier on the local PE (denoted as <AGI, source AII or SAII>) is
   called the source attachment identifier (SAI) and the endpoint
   identifier on the remote PE (denoted as <AGI, target AII or TAII>) is
   called the target attachment identifier (TAI). The SAI and TAI can be
   distinct values. This is useful for applications and provisioning
   models where the local PE (with a particular SAI) does not know and
   must somehow learn (e.g. via MP-BGP auto-discovery) of remote TAI
   values prior to launching PW setup messages towards the remote PE.

   The use of the GID FEC TLV provides the flexibility to structure
   (source or target) AII values to best fit particular application or
   provisioning model needs [L2VPN-SIG]. For example an AII structure
   that enables many individual AII values to be identified as a single
   value could significantly reduce the burden on AII distribution
   mechanisms (e.g. MP-BGP) and on PE memory needed to store this AII
   information. It should be noted that PWE3 signaling messages will
   always include a fully qualified AII value.

   An AII that is globally unique would facilitate PW management and
   security in large inter-AS and inter-provider environments. Providers
   would not have to worry about AII value overlap during provisioning
   or the need for AII network address translation (NAT) boxes during
   signaling. Globally unique AII values could aid in troubleshooting
   and could be subjected to source-validity checks during AII
   distribution and signaling. An AII automatically derived from a
   provider's existing IP address space can simplify the provisioning

   This document defines an AII structure based on [RFC4447] that:

     o Enables many discrete attachment individual identifiers to be
       summarized into a single AII summary value. This will enhance
       scalability by reducing the burden on AII distribution mechanisms
       and on PE memory.

     o Ensures global uniqueness if desired by the provider. This will
       facilitate Internet-wide PW connectivity and provide a means for
       providers to perform source validation on the AII distribution
       (e.g. MP-BGP) and signaling (e.g.  LDP) channels.

   This is accomplished by defining new AII types and the associated
   formats of the value field.

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3. Structure for the New AII Type

   [RFC4447] defines the format of the GID FEC TLV and the use and
   semantics of the attachment group identifier (AGI).

3.1. AII Type 1

   AII Type 1 has been allocated by IANA for use with provisioning
   models requiring a fixed-length 32-bit value [L2VPN-SIG]. This value
   is unique on the local PE.

3.2. AII Type 2

   The AII Type 2 structure permits varying levels of AII summarization
   to take place thus reducing the scaling burden on the aforementioned
   AII distribution mechanisms and PE memory. In other words it no
   longer becomes necessary to distribute or configure all individual
   AII values (which could number in the tens of thousands or more) on
   local PEs prior to establishing PWs to remote PEs. The details of how
   and where the aggregation of AII values is performed and then
   distributed as AII reachability information are not discussed in this

   AII Type 2 uses a combination of a provider's globally unique
   identifier (Global ID), a 32-bit prefix field and an optional 4-octet
   attachment circuit identifier field to create globally unique AII

   The encoding of AII Type 2 is shown in figure 1.

    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
   |  AII Type=02  |    Length     |        Global ID              |
   |       Global ID (contd.)      |        Prefix                 |
   |       Prefix (contd.)         |        AC ID                  |
   |      AC ID                    |

                      Figure 1 AII Type 2 TLV Structure

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     o AII Type = 0x02

     o Length = length of value field in octets. The length is set to 8
       if the AC ID is NULL and 12 if the AC ID is non-null.

     o Global ID = This is a 4 octet field containing a value that is
       unique to the provider. The global ID can contain the 2 octet or
       4 octet value of the provider's Autonomous System Number (ASN).
       It is expected that the global ID will be derived from the
       globally unique ASN of the autonomous system hosting the PEs
       containing the actual AIIs. The presence of a global ID based on
       the provider's ASN ensures that the AII will be globally unique.

       If the PE hosting the AIIs is present in an autonomous system
       where the provider is not running BGP, chooses not to expose this
       information or does not wish to use the global ID, then the
       global ID field MUST be set to zero.  If the global ID is derived
       from a 2-octet AS number, then the high-order 4 octets of this 4
       octet field MUST be set to zero.

       Please note that the use of the provider's ASN as a global ID
       DOES NOT have anything at all to do with the use of the ASN in
       protocols such as BGP.

     o Prefix = The 32-bit prefix is a value assigned by the provider or
       it can be automatically derived from the PE's /32 IPv4 loopback
       address. Note that it is not required that the 32-bit prefix have
       any association with the IPv4 address space used in the
       provider's IGP or BGP for IP reachability.

     o Attachment Circuit (AC) ID = This is a fixed length four octet
       field used to further refine identification of an attachment
       circuit on the PE. The inclusion of the AC ID is used to identify
       individual attachment circuits that share a common prefix.  If
       the AC ID is not present then the AC ID field MUST be null and
       the AII Length field is set to 8. If the AC ID is present then
       the length field is set to 12 octets.

4. IANA Considerations

   This document requests that IANA allocate a value from the
   "Attachment Individual Identifier (AII) Type" registry defined in

   The suggested value for this AII type is 0x02.

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5. Security Considerations

   AII values appear in AII distribution protocols [MP-BGP-AUTO-DISC]
   and PW signaling protocols [RFC4447] and are subject to various
   authentication schemes (i.e. MD5) if so desired.

   The use of global ID values (e.g. ASN) in the inter-provider case
   could enable a form of source-validation checking to ensure that the
   AII value (aggregated or explicit) originated from a legitimate

6. Acknowledgments

   Thanks to Carlos Pignataro, Scott Brim, Skip Booth, George Swallow
   and Bruce Davie for their input into this document.

7. Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

8. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

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   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-

9. Normative References

   [RFC4447], "Pseudowire Setup and Maintenance Using the Label
        Distribution Protocol (LDP)", RFC4447, April 2006

   [RFC4446], "IANA Allocations for Pseudowire Edge to Edge
        Emulation (PWE3)", RFC4446, April 2006

   [L2VPN-SIG], "Provisioning, Autodiscovery, and Signaling in
        L2VPNs", draft-ietf-l2vpn-signaling-08.txt, B. Davie, et
        al., May 2006

   [MP-BGP-AUTO-DISC], "Using BGP as an Auto-Discovery
        Mechanism for Layer-3 and Layer-2 VPNs", Ould-Brahim, H. et
        al, draft- ietf-l3vpn-bgpvpn-auto-06.txt, June 2005

10. Author Information

   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112

   Chris Metz
   Cisco Systems, Inc.
   3700 Cisco Way
   San Jose, Ca. 95134

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   Florin Balus
   3500 Carling Ave.
   Ottawa, Ontario, CANADA

   Jeff Sugimoto
   Nortel Networks
   3500 Carling Ave.
   Ottawa, Ontario, CANADA

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