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rfc:rfc5003

Network Working Group C. Metz Request for Comments: 5003 L. Martini Category: Standards Track Cisco Systems Inc.

                                                              F. Balus
                                                        Alcatel-Lucent
                                                           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.

Abstract

 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

Metz, et al. Standards Track [Page 1] RFC 5003 AII Types for Aggregation September 2007

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.

Metz, et al. Standards Track [Page 2] RFC 5003 AII Types for Aggregation September 2007

 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",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 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
 document.
 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.

Metz, et al. Standards Track [Page 3] RFC 5003 AII Types for Aggregation September 2007

 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
     12.
   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.

Metz, et al. Standards Track [Page 4] RFC 5003 AII Types for Aggregation September 2007

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
 source.

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.

Metz, et al. Standards Track [Page 5] RFC 5003 AII Types for Aggregation September 2007

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
 Alcatel-Lucent
 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

Metz, et al. Standards Track [Page 6] RFC 5003 AII Types for Aggregation September 2007

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Metz, et al. Standards Track [Page 7]

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