RFC5003: Attachment Individual Identifier (AII) Types for Aggregation

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Related keywords:  (pseudowire) (TLV)

Network Working Group                                            C. Metz
Request for Comments: 5003                                    L. Martini
Category: Standards Track                             Cisco Systems Inc.
                                                                F. Balus
                                                             J. Sugimoto
                                                         Nortel Networks
                                                          September 2007

      Attachment Individual Identifier (AII) Types for Aggregation

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   The signaling protocols used to establish point-to-point pseudowires
   include type-length-value (TLV) fields that identify pseudowire
   endpoints called attachment individual identifiers (AIIs).  This
   document defines AII structures in the form of new AII TLV fields
   that support AII aggregation for improved scalability and Virtual
   Private Network (VPN) auto-discovery.  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 provider edge (PE) nodes based on customer need.

Table of Contents

   1. Introduction ....................................................2
   2. Specification of Requirements ...................................3
   3. Structure for the New AII Type ..................................3
      3.1. AII Type 1 .................................................3
      3.2. AII Type 2 .................................................3
   4. IANA Considerations .............................................5
   5. Security Considerations .........................................5
   6. Acknowledgments .................................................5
   7. Normative References ............................................5
   8. Informative References ..........................................5

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1.  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.

   The GID FEC element includes TLV fields for attachment individual
   identifiers (AIIs) 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 Multiprotocol BGP (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 the needs of a particular
   application or provisioning model [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 Pseudowire
   Emulation Edge-to-Edge (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 (autonomous system) 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 process.

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   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.

2.  Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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 a 4-octet
   attachment circuit identifier (AC ID) field to create globally unique
   AII values.

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   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

   o AII Type = 0x02

     o Length = length of value field in octets.  The length is set to

     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 global ID is derived from a 2-octet AS number, then the
       two high-order 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, for IP reachability, 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.

     o Attachment Circuit (AC) ID = This is a fixed-length 4-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.

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4.  IANA Considerations

   IANA has allocated a value from the "Attachment Individual Identifier
   (AII) Type" registry defined in [RFC4446].

   The value for this AII type is 0x02.

5.  Security Considerations

   AII values appear in AII distribution protocols [L2VPN-SIG] 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.  Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4447]   Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
               G. Heron, "Pseudowire Setup and Maintenance Using the
               Label Distribution Protocol (LDP)", RFC 4447, April 2006.

   [RFC4446]   Martini, L., "IANA Allocations for Pseudowire Edge to
               Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

8.  Informative References

   [L2VPN-SIG] Rosen, E., Luo, W., Davie, B., and V. Radoaca,
               "Provisioning, Autodiscovery, and Signaling in L2VPNs",
               Work in Progress, May 2006.

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Authors' Addresses

   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO, 80112
   EMail: lmartini@cisco.com

   Chris Metz
   Cisco Systems, Inc.
   3700 Cisco Way
   San Jose, Ca. 95134
   EMail: chmetz@cisco.com

   Florin Balus
   701 East Middlefield Rd.
   Mountain View, CA 94043
   EMail: florin.balus@alcatel-lucent.com

   Jeff Sugimoto
   Nortel Networks
   3500 Carling Ave.
   Ottawa, Ontario, CANADA
   EMail: sugimoto@nortel.com

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RFC 5003               AII Types for Aggregation          September 2007

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