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     Network Working Group                                        Chris Metz
     Internet Draft                                             Luca Martini
     Expires: May 2006                                         Cisco Systems
     
                                                                Florin Balus
                                                               Jeff Sugimoto
                                                             Nortel Networks
     
                                                            October 20, 2005
     
     
     
                              AII Types for Aggregation
                           draft-metz-aii-aggregate-01.txt
     
     
     
     
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     Copyright Notice
     
        Copyright (C) The Internet Society (2005).  All Rights Reserved.
     
     Abstract
     
        [PWE3 Control] defines the signaling mechanisms for establishing
        point-to-point pseudowires between two provider edge (PE) nodes. The
        Generalized ID FEC element contained in PWE3 signaling protocols
        include TLV fields that identify pseudowire endpoints called
        attachment individual identifiers (AII). This document defines an AII
        structure in the form of new AII type-length-value fields that
        supports AII aggregation for improved scalability. 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.
     
     Conventions used in this document
     
        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 RFC-2119 Error!
        Reference source not found..
     
     Table of Contents
     
     
        1. Introduction...................................................2
        2. Structure for New AII Types....................................4
           2.1. PWid AII Type.............................................4
           2.2. Short Prefix AII Type.....................................5
           2.3. Long Prefix AII Type......................................7
        3. IANA Considerations............................................9
        4. Security Considerations........................................9
        5. Acknowledgments...............................................10
        Author's Addresses...............................................11
        Intellectual Property Statement..................................12
        Disclaimer of Validity...........................................12
        Copyright Statement..............................................13
        Acknowledgment...................................................13
     
     1. Introduction
     
        [PWE3-CONTROL] 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
     
     
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        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 (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 summarizes or aggregates a large number of individual AII values
        could significantly reduce the burden on AII distribution mechanisms
        (e.g. MP-BGP) and on PE memory needed to store this AII information.
     
        An aggregate AII structure and corresponding IP next hop address
        could form the basis for enabling inter-domain MS-PW routing and
        signaling in a manner similar to the way that BGP-advertised IP
        address prefixes and next hops enable inter-domain IP routing. This
        would be useful in large inter-domain VPWS networks where PWs are
        established between local and remote PE based on customer need [REQ-
        MH-PW]. Note that this document does not discuss if, how, or where in
        the network the aggregation of AII values is performed, how AII
        aggregate reachability is distributed nor does it discuss how PW
        setup messages are routed through a network based on AII reachability
        information.
     
        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 “NATs” during signaling. Globally unique AII
        values could aid in troubleshooting and could be subjected to source-
        validity checks during AII distribution and signaling.
     
     
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        An AII automatically derived from a provider’s existing IP address
        space can simplify the provisioning process. In addition an AII
        structure that is backwards compatible with previous endpoint
        identifier semantics (i.e. PWid) and other L2VPN provisioning models
        [L2VPN-SIG] would help providers to converge upon a PW provisioning
        and signaling behavior employing GID FEC TLVs.
     
        In summary the purpose of this document is to define an AII structure
        based on [PWE3-CONTROL] that:
     
        o  Enables many discrete attachment individual identifiers to be
           aggregated into a single AII aggregate. 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.
     
     
        o  Supports a uniform PW signaling mechanism employing the GID FEC
           TLV structure for endpoints provisioned with the AII types defined
           in this document, other L2VPN provisioning techniques and
           including those previously configured with the older FEC 128 PWid
           value.
     
        This is accomplished by defining three new AII types and associated
        formats of the value fields.
     
     2. Structure for New AII Types
     
        [PWE3-CONTROL] defines the format of the GID FEC TLV and the use and
        semantics of the attachment group identifier (AGI).
     
        New AII types and the format of their associated AII value fields are
        defined next.
     
     2.1. PWid AII Type
     
        The PWid AAI type provides GID FEC 129 signaling compatibility with
        those endpoint identifiers provisioned with the 32-bit PWid values.
        Unlike the FEC 128 encoding, the values of the PWid AII type do not
        have to match on the local and remote PE nodes.
     
     
     
     
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        The PWid AII type can also be used when the provisioning model
        warrants definition of a fixed-length 32-bit value used to identify
        a particular attachment circuit [L2VPN-SIG]. The value of the PWid
        AII type can be globally unique or combined with some other value
        (e.g. AGI) to provide a globally unique identifier if warranted by
        the provisioning model.
     
        The PWid AII type is encoded as the following:
     
         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=01 |    Length     |        PWid                   |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |           PWid     (contd.)   |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
     
        o  AII Type = 0x01
     
     
        o  Length = Length of the value field in octets. The length is set to
           4 for this AII type.
     
     
        o  PWid = Fixed-length 32-bit value.
     
     
        The provisioning models employing this AII type require that the
        entire 32-bit value field (fully-qualified) is processed by AII
        distribution mechanisms. This means it CANNOT be aggregated.
     
     
     
     2.2. Short Prefix AII Type
     
        The Short Prefix AII type 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.
     
     
     
     
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        The Short Prefix AII type 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 values. It is termed the Short Prefix AII type because of the
        shorter 32-bit prefix used here as compared to the longer 256-bit
        prefix used in the Long Prefix AII type defined in the next section.
     
        The encoding of the Short Prefix AII type 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                             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                             AC ID                             |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
     
                       Figure 1 Short Prefix AII TLV Structure
     
     
     
        o  AII Type = 0x02
     
     
        o  Length = length of value field in octets. The length is set to 10
           if the AC ID is NULL and 14 if the AC ID is non-null.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        o  Global ID = This is a 6 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, a global
           unicast IPv6 /48 prefix assigned to the provider or some other
           globally unique value up to 6 octets in length. It is expected
           that the global ID will be derived from the globally unique AS
           number of the autonomous system hosting the PEs containing the
           actual AIIs. 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 AS number as a global
           ID DOES NOT have anything at all to do with the use of the AS
           number 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 10. If the AC ID is present then
           the length field is set to 14 octets.
     
     
     
     2.3. Long Prefix AII Type
     
        The Long Prefix AII type employs a global ID and 256-bit prefix field
        (versus 32 bits for the Short Prefix AII type) to create AII values.
        The Long Prefix AII type might be useful to providers with
        provisioning systems or AII addressing schemes that exceed 32 bits in
        length. It can also be used to auto-generate AII values based on /128
        IPv6 and /32 IPv4 PE loopbacks.
     
        The encoding of the Long Prefix AII type is shown in figure 2:
     
     
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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
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        | AII Type=03   |    Length     |        Global ID              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                          Global ID (contd.)                   |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                                                               |
        |                                                               |
        |                                                               |
        |                            Prefix                             |
        |                                                               |
        |                                                               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     
                       Figure 2 Long Prefix AII TLV Structure
     
     
        o  AII Type = 0x03
     
     
        o  Length = length of value field in octets. The length is set to 38
           for this AII type.
     
     
        o  Global ID = This is a 6 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, a global
           unicast IPv6 /48 prefix assigned to the provider or some other
           globally unique value up to 6 octets in length. It is expected
           that the global ID will be derived from the globally unique AS
           number of the autonomous system hosting the PEs containing the
           actual AIIs. 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 AS number as a global
           ID DOES NOT have anything at all to do with the use of the AS
           number used in protocols such as BGP.
     
     
     
     
     
     
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        o  Prefix = The 256-bit Prefix is a value assigned by the provider or
           it can be automatically derived from the PE’s local addressing
           scheme such as IPv6 or IPv4.
     
     
        This AII type does not employ an optional AC ID field. This is
        because there are sufficient bits available in the prefix field to
        hold a fully qualified target PE value auto-generated from even a
        long address type such as IPv6 with the remainder available for local
        attachment circuit identification.
     
     
     
     3. IANA Considerations
     
        This document requests that IANA allocate three AII types from the
        "Attachment Individual Identifier (AII) Type" registry defined in
        [IANA].
     
        The suggested values for the AAI types are:
     
        Value       Description
     
        0x01        PWid
     
        0x02        Short Prefix
     
        0x03        Long Prefix
     
     
     
     4. Security Considerations
     
        AII values appear in AII distribution protocols [MP-BGP-AUTO-DISC]
        and PW signaling protocols [PWE3-CONTROL] 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.
     
     
     
     
     
     
     
     
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     5. Acknowledgments
     
        Thanks to Carlos Pignataro, Scott Brim, Skip Booth, George Swallow
        and Bruce Davie for their input into this document.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        References
     
        [PWE3-CONTROL], “Pseudowire Setup and Maintenance using LDP”,
                  draft-ietf-pwe3-control-protocol-17.txt, June 2005
     
     
     
        [IANA], "IANA Allocations for pseudo Wire Edge to Edge Emulation
                  (PWE3)" Martini,Townsley, draft-ietf-pwe3-iana-allocation-
                  12.txt, work in progress), September 2005
     
     
     
        [L2VPN-SIG], “Provisioning Models and Endpoint Identifiers in L2VPN
                  Signaling”, draft-ietf-l2vpn-signaling-06.txt, Sept. 2005
     
     
     
        [REQ-MH-PW], “Requirements for inter domain Pseudo-Wires”,  draft-
                  ietf-pwe3-ms-pw-requirements-00.txt, Internet Draft, June
                  2005
     
     
     
        [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
     
     
     
     Author's Addresses
     
     Chris Metz
     Cisco Systems, Inc.
     3700 Cisco Way
     San Jose, Ca. 95134
     Email: chmetz@cisco.com
     
     Luca Martini
     Cisco Systems, Inc.
     9155 East Nichols Avenue, Suite 400
     Englewood, CO, 80112
     Email: lmartini@cisco.com
     
     Florin Balus
     Nortel
     3500 Carling Ave.
     
     
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     Ottawa, Ontario, CANADA
     Email: balus@nortel.com
     
     Jeff Sugimoto
     Nortel
     3500 Carling Ave.
     Ottawa, Ontario, CANADA
     Email: sugimoto@nortel.com
     
     
     
     
     
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     Copyright Statement
     
        Copyright (C) The Internet Society (2005).
     
        This document is subject to the rights, licenses and restrictions
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