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Versions: (draft-swallow-mpls-tp-identifiers) 00 01 02 03 04 05 06 07 RFC 6370

MPLS Working Group                                              M. Bocci
Internet-Draft                                            Alcatel-Lucent
Intended status: Standards Track                              G. Swallow
Expires: September 4, 2011                                         Cisco
                                                                 E. Gray
                                                                Ericsson
                                                           March 3, 2011


                          MPLS-TP Identifiers
                   draft-ietf-mpls-tp-identifiers-04

Abstract

   This document specifies identifiers for MPLS-TP objects.  Included
   are identifiers conformant to existing ITU conventions and
   identifiers which are compatible with existing IP, MPLS, GMPLS, and
   Pseudowire definitions.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 4, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
     1.3.  Notational Conventions in Backus-Naur Form . . . . . . . .  4
   2.  Named Entities . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Uniquely Identifying an Operator . . . . . . . . . . . . . . .  5
     3.1.  The Global ID  . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  ITU Carrier Code . . . . . . . . . . . . . . . . . . . . .  6
   4.  Node and Interface Identifiers . . . . . . . . . . . . . . . .  6
   5.  MPLS-TP Tunnel and LSP Identifiers . . . . . . . . . . . . . .  7
     5.1.  MPLS-TP Point to Point Tunnel Identifiers  . . . . . . . .  8
     5.2.  MPLS-TP LSP Identifiers  . . . . . . . . . . . . . . . . .  8
       5.2.1.  MPLS-TP Co-Routed Bidirectional LSP Identifiers  . . .  8
       5.2.2.  MPLS-TP Associated Bidirectional LSP Identifiers . . .  9
     5.3.  Mapping to GMPLS and RSVP-TE Signalling  . . . . . . . . .  9
   6.  Pseudowire Path Identifiers  . . . . . . . . . . . . . . . . . 10
   7.  Maintenance Identifiers  . . . . . . . . . . . . . . . . . . . 11
     7.1.  Maintenance Entity Group Identifiers . . . . . . . . . . . 11
       7.1.1.  ICC-based MEG Identifiers  . . . . . . . . . . . . . . 12
       7.1.2.  IP Compatible MEG_IDs  . . . . . . . . . . . . . . . . 12
         7.1.2.1.  MPLS-TP LSP MEG_IDs  . . . . . . . . . . . . . . . 12
         7.1.2.2.  Pseudowire MEG_IDs . . . . . . . . . . . . . . . . 12
     7.2.  MEP_IDs  . . . . . . . . . . . . . . . . . . . . . . . . . 12
       7.2.1.  ICC-based MEP Identifiers  . . . . . . . . . . . . . . 12
       7.2.2.  IP based MEP_IDs . . . . . . . . . . . . . . . . . . . 13
         7.2.2.1.  MPLS-TP LSP_MEP_ID . . . . . . . . . . . . . . . . 13
         7.2.2.2.  MEP_IDs for Pseudowires  . . . . . . . . . . . . . 13
         7.2.2.3.  Pseudowire Segments Endpoint IDs . . . . . . . . . 13
     7.3.  MIP Identifiers  . . . . . . . . . . . . . . . . . . . . . 14
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16










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1.  Introduction

   This document specifies identifiers to be used in within the
   Transport Profile of Multiprotocol Label Switching (MPLS-TP).  The
   MPLS-TP requirements (RFC 5654) [7] require that the elements and
   objects in an MPLS-TP environment are able to be configured and
   managed without a control plane.  In such an environment many
   conventions for defining identifiers are possible.  This document
   defines identifiers for MPLS-TP management and OAM functions suitable
   to ITU conventions and to IP/MPLS conventions.  Applicability of the
   different identifier schemas to different applications is outside the
   scope of this document.

1.1.  Terminology

   AII: Attachment Interface Identifier

   ASN: Autonomous System Number

   FEC: Forwarding Equivalence Class

   GMPLS: Generalized Multi-Protocol Label Switching

   ICC: ITU Carrier Code

   LSP: Label Switched Path

   LSR: Label Switching Router

   ME: Maintenance Entity

   MEG: Maintenance Entity Group

   MEP: Maintenance Entity Group End Point

   MIP: Maintenance Entity Group Intermediate Point

   MPLS: Multi-Protocol Label Switching

   NNI: Network-to-Network Interface

   OAM: Operations, Administration and Maintenance

   P2MP: Point to Multi-Point

   P2P: Point to Point

   PW: Pseudowire



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   RSVP: Resource Reservation Protocol

   RSVP-TE: RSVP Traffic Engineering

   S-PE: Switching Provider Edge

   T-PE: Terminating Provider Edge

1.2.  Requirements Language

   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 [1].

1.3.  Notational Conventions in Backus-Naur Form

   All multiple-word atomic identifiers use underscores (_) between the
   words to join the words.  Many of the identifiers are composed of a
   concatenation of other identifiers.  These are expressed using
   Backus-Naur Form (using double-colon - "::" - notation).

   Where the same identifier type is used multiple times in a
   concatenation, they are qualified by a prefix joined to the
   identifier by a dash (-).  For example East-Node_ID is the Node_ID of
   a node referred to as East.


2.  Named Entities

   In order to configure, operate and manage a transport network based
   on the MPLS Transport Profile, a number of entities require
   identification.  Identifiers for the follow entities are defined in
   this document:

   o  Operator

      *  Global_ID

      *  ICC

   o  LSR

   o  LSP

   o  PW

   o  Interface




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   o  MEG

   o  MEP

   o  MIP

   o  Tunnel

   Note that we have borrowed the term tunnel from RSVP-TE (RFC 3209)
   [2] where it is used to describe an entity that provides a logical
   association between a source and destination LSR.  The tunnel in turn
   is instantiated by one or more LSPs, where the additional LSPs are
   used for protection or re-grooming of the tunnel.


3.  Uniquely Identifying an Operator

   An operator is uniquely identified by an Operator Identifier
   (Opr_ID).  Two formats are defined, one that is compatible with IP
   operational practice called a Global_ID and or one compatible with
   ITU practice, the ICC.  An The Opr_ID MAY use either the Global_ID or
   ICC format.

3.1.  The Global ID

   RFC 5003 [3] defines a globally unique Attachment Interface
   Identifier (AII).  That AII is composed of three parts, a Global_ID
   which uniquely identifies a operator, a prefix, and finally and
   attachment circuit identifier.  We have chosen to use that Global ID
   for MPLS-TP.  Quoting from RFC 5003, section 3.2, "The global ID can
   contain the 2-octet or 4-octet value of the operator'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 operator's ASN ensures that the AII will be globally
   unique."

   When the Global_ID is derived from a 2-octet AS number, the two high-
   order octets of this 4-octet identifier MUST be set to zero.  Further
   ASN 0 is reserved.  A Global_ID of zero means that no Global_ID is
   present.  Note that a Global_ID of zero is limited to entities
   contained within a single operator and MUST NOT be used across an
   NNI.  A non-zero Global_ID MUST be derived from an ASN owned by the
   operator.

   Note that this Global_ID is used solely to provide a globally unique
   context for other MPLS-TP identifiers.  It has nothing to do with the
   use of the ASN in protocols such as BGP.



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3.2.  ITU Carrier Code

   M.1400 defines the ITU Carrier Code (ICC) assigned to a network
   operator/service provider and maintained by the ITU-T
   Telecommunication Standardization Bureau (TSB): www.itu.int/ITU-T/
   inr/icc/index.html.

   ICCs can be assigned both to ITU-T and non-ITU-T members and the
   referenced local ICC website may contain ICCs of operators of both
   kinds.

   The ICC is a string of one to six characters, each character being
   either alphabetic (i.e.  A-Z) or numeric (i.e. 0-9) characters.
   Alphabetic characters in the ICC SHOULD be represented with upper
   case letters.


4.  Node and Interface Identifiers

   An LSR requires identification of the node itself and of its
   interfaces.  An interface is the attachment point to a server layer
   MPLS-TP section or MPLS-TP tunnel.

   We call the identifier associated with a node a Node Identifier
   (Node_ID).  The Node_ID is a unique 32-bit value assigned by the
   operator within the scope of the Global_ID.  The structure of the
   Node_ID is operator specific and is outside the scope of this
   document.  However, the value zero is reserved and MUST NOT be used.
   Where IPv4 addresses are used, it may be convenient to use the Node's
   IPv4 loopback address as the Node_ID, however the Node_ID does not
   need to have any association with the IPv4 address space used in the
   operator's IGP or BGP.  Where IPv6 addresses are used exclusively, a
   32-bit value unique within the scope of the Global_ID is assigned.

   A LSR can support multiple layers (e.g. hierarchical LSPs) and the
   Node_ID belongs to the multiple layer context i.e. it is applicable
   to all LSPs or PWs that originate on, have a midpoint on, or
   terminate on the node.

   In situations where a Node_ID needs to be globally unique, this is
   accomplished by prefixing the identifier with the operator's Opr_ID.
   The particular combination of Global_ID::Node_ID we call a Global
   Node ID or Global_Node_ID.

   Within the context of a particular node, we call the identifier
   associated with an interface an Interface Number or IF_Num. The
   IF_Num is a 32-bit unsigned integer assigned by the operator and MUST
   be unique within the scope of a Node_ID.  The IF_Num value 0 has



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   special meaning (see section , MIP Identifiers) (Section 7.3) and
   MUST NOT be used to identify an MPLS-TP interface.

   An Interface Identifier or IF_ID identifies an interface uniquely
   within the context of an Opr_ID.  It is formed by concatenating the
   Node_ID with the IF_Num. That is an IF_ID is a 64-bit identifier
   formed as Node_ID::IF_Num.

   This convention was chosen to allow compatibility with GMPLS.  GMPLS
   signaling [4] requires interface identification.  GMPLS allows three
   formats for the Interface_ID.  The third format consists of an IPv4
   Address plus a 32-bit unsigned integer for the specific interface.
   The format defined for MPLS-TP is consistent with this format, but
   uses the Node_ID instead of an IPv4 Address.

   If an IF_ID needs to be globally unique, this is accomplished by
   prefixing the identifier with the operator's Opr_ID.

   The attachment point to an MPLS-TP Tunnel (see section Section 5.1
   also needs an interface identifier.  Note that MPLS-TP supports
   hierarchical tunnels.  The attachment point to a MPLS-TP Tunnel at
   any sub layer requires a unique IF_ID.


5.  MPLS-TP Tunnel and LSP Identifiers

   In MPLS the actual transport of packets is provided by label switched
   paths (LSPs).  A transport service may be composed of multiple LSPs.
   Further the LSPs providing a service may change over time due to
   protection and restoration events.  In order to clearly identify the
   service we use the term "MPLS-TP Tunnel" or simply "tunnel" for a
   service provided by (for example) a working LSP and protected by a
   protection LSP.  The Tunnel_ID identifies the transport service and
   provides a stable binding to the client in the face of changes in the
   the data plane LSPs used to provide the service due to protection and
   restoration events.  This section defines an MPLS-TP Tunnel_ID to
   uniquely identify a tunnel and MPLS-TP LSP_IDs within the context of
   that tunnel.

   For the case where multiple LSPs (for example) are used to support a
   single service with a common set of end-points, using this identifier
   allows for a trivial mapping between the server and client layers to
   a common service identifier which may be either defined by, or used
   by, the client.

   Note that this usage is not intended to constrain protection schemes,
   and may be used to identify any service (protected or un-protected)
   that may appear to the client as a single service attachment point.



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   Keeping the tunnel number consistent across working and protection
   LSPs is a useful construct currently employed within GMPLS.  However
   there is no requirement that a protection LSP use the same tunnel
   number as the working LSP.

5.1.  MPLS-TP Point to Point Tunnel Identifiers

   At each endpoint a tunnel is uniquely identified by the endpoint's
   Node_ID and a locally assigned tunnel number.  Specifically a
   Tunnel_Num is a 16-bit unsigned integer unique within the context of
   the Node_ID.  The motivation for each endpoint having its own tunnel
   number is to allow a compact form for the MEP-ID.  See section
   Section 7.1.2.1.

   Having two tunnel numbers also serves to simplify other signaling
   (e.g., setup of associated bi-directional tunnels as described in
   section Section 5.3.)

   The concatenation of the two endpoint identifiers serves as the full
   identifier.  In a configured environment the endpoints are often
   called East and West.  Using this convention the format of the format
   of a Tunnel_ID is:

      East-Node_ID::East-Tunnel_Num::West-Node_ID::West-Tunnel_Num

   Where the Tunnel_ID needs to be globally unique, this is accomplished
   by using globally unique Node_IDs as defined above.  Thus a globally
   unique Tunnel_ID becomes:

      East-Global_Node_ID::East-Tunnel_Num::West-Global_Node_ID::
      West-Tunnel_Num

   When an MPLS-TP Tunnel is configured, it MUST be assigned a unique
   IF_ID at both the source and destination endpoints.  As usual, the
   IF_ID is composed of the local NODE_ID concatenated with a 32-bit
   IF_Num.

5.2.  MPLS-TP LSP Identifiers

5.2.1.  MPLS-TP Co-Routed Bidirectional LSP Identifiers

   For a co-routed bidirectional LSP can be uniquely identified by a
   single LSP number within the scope of an MPLS-TP Tunnel_ID.
   Specifically an LSP_Num is a 16-bit unsigned integer unique within
   the Tunnel_ID.  Thus the format of a LSP_ID is:

      East-Node_ID::East-Tunnel_Num::West-Node_ID::West-
      Tunnel_Num::LSP_Num



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   Where the LSP_ID needs to be globally unique, this is accomplished by
   using globally unique Node_IDs as defined above.  Thus a globally
   unique LSP_ID becomes:

      East-Global_Node_ID::East-Tunnel_Num::West-Global_Node_ID::
      West-Tunnel_Num::LSP_Num

   The corresponding ICC-based version of this identifier would be:
      East-ICC::East-Node_ID::East-Tunnel_Num::West-ICC::West-Node_ID::
      West-Tunnel_Num::LSP_Num

5.2.2.  MPLS-TP Associated Bidirectional LSP Identifiers

   For an associated bidirectional LSP each of the unidirectional LSPs
   from East to West and West to East require LSP IDs.  The each LSP can
   be uniquely identified by a single LSP number within the scope of the
   senders Tunnel_Num. Specifically an LSP_Num is a 16-bit unsigned
   integer unique within the Tunnel_Num. Thus the format of a LSP_ID is:

      East-Node_ID::East-Tunnel_Num::East-LSP_Num::

      West-Node_ID::West-Tunnel_Num::West-LSP_Num

   Where the LSP_ID needs to be globally unique, this is accomplished by
   using globally unique Node_IDs as defined above.  Thus a globally
   unique LSP_ID becomes:

      East-Global_Node_ID::East-Tunnel_Num::East-LSP_Num::
      West-Global_Node_ID::West-Tunnel_Num::West-LSP_Num

   The corresponding ICC-based version of this identifier would be:

      East-ICC::East-Node_ID::East-Tunnel_Num::East-LSP_Num::
      West-ICC::West-Node_ID::West-Tunnel_Num::West-LSP_Num

5.3.  Mapping to GMPLS and RSVP-TE Signalling

   This section defines the mapping from an MPLS-TP LSP_ID to GMPLS.  At
   this time, GMPLS has yet to be extended to accommodate Global_IDs.
   Thus a mapping is only made for the network unique form of the
   LSP_ID.

   GMPLS signaling [5] uses a 5-tuple to uniquely identify an LSP within
   a operator's network.  This tuple is composed of a Tunnel Endpoint
   Address, Tunnel_ID, Extended Tunnel ID, and Tunnel Sender Address and
   (GMPLS) LSP_ID.

   In situations where a mapping to the GMPLS 5-tuple is required, the



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   following mapping is used.

   o  Tunnel Endpoint Address = West-Node_ID

   o  Tunnel_ID = East-Tunnel_Num

   o  Extended Tunnel_ID = East-Node_ID

   o  Tunnel Sender Address = East-Node_ID

   o  LSP_ID = East-LSP_Num

   An associated bi-directional LSP between two nodes East and West
   consists of two uni-directional LSPs, one from East to West and one
   from West to East.  RSVP-TE is capable of signaling such LSPs.

   In situations where a mapping to the RSVP 5-tuples is required, the
   following mappings are used.  For the East to West LSP the mapping
   would be:

   o  Tunnel Endpoint Address = West-Node_ID

   o  Tunnel_ID = East-Tunnel_Num

   o  Extended Tunnel_ID = East-Node_ID

   o  Tunnel Sender Address = East-Node_ID

   o  LSP_ID = East-LSP_Num

   Likewise, the East to West LSP the mapping would be:

   o  Tunnel Endpoint Address = East-Node_ID

   o  Tunnel_ID = West-Tunnel_Num

   o  Extended Tunnel_ID = West-Node_ID

   o  Tunnel Sender Address = West-Node_ID

   o  LSP_ID = West-LSP_Num


6.  Pseudowire Path Identifiers

   Pseudowire signaling (RFC 4447 [6]) defines two FECs used to signal
   pseudowires.  Of these, FEC Type 129 along with AII Type 2 as defined
   in RFC 5003 [3] fits the identification requirements of MPLS-TP.



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   In an MPLS-TP environment, a PW is identified by a set of identifiers
   which can be mapped directly to the elements required by FEC 129 and
   AII Type 2.  To distinguish this identifier from other Pseudowire
   Identifiers, we call this a Pseudowire Path Identifier or PW_Path_Id.

   The AII Type 2 is composed of three fields.  These are the Global_ID,
   the Prefix, and the AC_ID.  The Global_ID used in this document is
   identical to the Global_ID defined in RFC 5003.  The Node_ID is used
   as the Prefix.  The AC_ID is as defined in RFC 5003.

   To complete the FEC 129, all that is required is a Attachment Group
   Identifier (AGI).  That field is exactly as specified in RFC 4447.
   FEC 129 has a notion of Source AII (SAII) and Target AII (TAII).
   These terms are used relative to the direction of the signaling.  In
   a purely configured environment when referring to the entire PW, this
   distinction is not critical.  That is a FEC 129 of AGIa::AIIb::AIIc
   is equivalent to AGIa::AIIc::AIIb.  We note that in a signaled
   environment, the required convention in RFC 4447 is that at a
   particular endpoint, the AII associated with that endpoint comes
   first.  The complete PW_Path_Id is:

      AGI::East-Global_Node_ID::East-AC_ID::West-Global_Node_ID::
      West-AC_ID.

   The corresponding ICC-based version for this identifier would be:

      AGI::East-ICC::East-Node_ID::East-AC_ID::West-ICC::West-Node_ID::
      West-AC_ID


7.  Maintenance Identifiers

   In MPLS-TP a Maintenance Entity Group (MEG) represents an Entity that
   requires management and defines a relationship between a set of
   maintenance points.  A maintenance point is either Maintenance Entity
   Group End-point (MEP) or a Maintenance Entity Group Intermediate
   Point (MIP).  Maintenance points are uniquely associated with a MEG.
   Within the context of a MEG, MEPs and MIPs must be uniquely
   identified.  This section defines a means of uniquely identifying
   Maintenance Entity Groups, Maintenance Entities and uniquely defining
   MEPs and MIPs within the context of a Maintenance Entity Group.

7.1.  Maintenance Entity Group Identifiers

   Maintenance Entity Group Identifiers (MEG_IDs) are required for
   MPLS-TP LSPs and Pseudowires.  Two classes of MEG_IDs are defined,
   one that follows the IP compatible identifier defined above as well
   as the ICC-format.



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7.1.1.  ICC-based MEG Identifiers

   MEG_ID for MPLS-TP LSPs and Pseudowires MAY use the globally unique
   ICC-based format.

   In this case, the MEG_ID is a string of up to thirteen characters,
   each character being either alphabetic (i.e.  A-Z) or numeric (i.e.
   0-9) characters.  It consists of two subfields: the ICC (as defined
   in section 3) followed by a unique MEG code (UMC).  The UMC MUST be
   unique within the organization identified by the ICC.

   The ICC MEG_ID may be applied equally to a single MPLS-TP LSP or
   Pseudowires.  Note that when encoded in a protocol such as in a TLV,
   a different type needs to be defined for LSP and PWs as the OAM
   capabilities may be different.

7.1.2.  IP Compatible MEG_IDs

7.1.2.1.  MPLS-TP LSP MEG_IDs

   Since a MEG pertains to a single MPLS-TP LSP, IP compatible MEG_IDs
   for MPLS-TP LSPs are simply the corresponding LSP_IDs.  We note that
   while the two identifiers are syntactically identical, they have
   different semantics.  This semantic difference needs to be made
   clear.  For instance if both a MPLS-TP LSP_ID and MPLS-TP LSP MEG_IDs
   are to be encoded in TLVs different types need to be assigned for
   these two identifiers.

7.1.2.2.  Pseudowire MEG_IDs

   For Pseudowires a MEG pertains to a single PW.  The IP compatible
   MEG_ID for a PW is simply the corresponding PW_Path_ID.  We note that
   while the two identifiers are syntactically identical, they have
   different semantics.  This semantic difference needs to be made
   clear.  For instance if both a PW_Path_ID and a PW_MEG_ID is to be
   encoded in TLVs different types need to be assigned for these two
   identifiers.

7.2.  MEP_IDs

7.2.1.  ICC-based MEP Identifiers

   ICC-based MEP_IDs for MPLS-TP LSPs and Pseudowires are formed by
   appending a unique number to the MEG_ID defined in section
   Section 7.1.1 above.  Within the context of a particular MEG, we call
   the identifier associated with a MEP the MEP Index (MEP_Index).  The
   MEP_Index is administratively assigned.  It is encoded as a 16-bit
   unsigned integer and MUST be unique within the MEG.  An ICC-based



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   MEP_ID is:

      MEG_ID::MEP_Index

   An ICC-based MEP ID is globally unique by construction given the ICC-
   based MEG_ID global uniqueness.

7.2.2.  IP based MEP_IDs

7.2.2.1.  MPLS-TP LSP_MEP_ID

   In order to automatically generate MEP_IDs for MPLS-TP LSPs, we use
   the elements of identification that are unique to an endpoint.  This
   ensures that MEP_IDs are unique for all LSPs within a operator.  When
   Tunnels or LSPs cross operator boundaries, these are made unique by
   pre-pending them with the operator's Global_ID.

   The MPLS-TP LSP_MEP_ID is

      Node_ID::Tunnel_Num::LSP_Num,

   where the Node_ID is the node in which the MEP is located and
   Tunnel_Num is the tunnel number unique to that node.  In the case of
   Associated Bi-directional LSPs, the LSP_Num unique to where the MEP
   resides.

   In situations where global uniqueness is required this becomes:

      Global_ID::Node_ID::Tunnel_Num::LSP_Num

7.2.2.2.  MEP_IDs for Pseudowires

   Like MPLS-TP LSPs, Pseudowire endpoints (T-PEs) require MEP_IDs.  In
   order to automatically generate MEP_IDs for PWs, we simply use the
   AGI plus the AII associated with that end of the PW.  Thus a MEP_ID
   used in end-to-end for an Pseudowire T-PE takes the form

      AGI:Global_ID::Node_ID::AC_ID,

   where the Node_ID is the node in which the MEP is located and the
   AC_ID is the AC_ID of the Pseudowire at that node.

7.2.2.3.  Pseudowire Segments Endpoint IDs

   In some OAM communications, messages are originated by the node at
   one end of a PW segment and relayed to the other end of that same
   segment by setting the TTL of the PW label to one (1).  For a multi-
   segment pseudowire, TTL could be set to any value that would cause



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   OAM messages to reach the target segment end-point (up to and
   including 255).  In such communications an identifier for the
   pseudowire segment endpoint.  We call this a Pseudowire Segments
   Endpoint ID or PW_SE_ID.

   The PW_SE_ID is formed by a combination of a PW MEP_ID and the
   identification of the local node.  At an S-PE, there are two PW
   segments.  We distinguish the segments by using the MEP_ID which is
   upstream of the PW segment in question.  To complete the
   identification we suffix this with the identification of the local
   node.


      +-------+         +-------+         +-------+         +-------+
      |       |         |       |         |       |         |       |
      |      A|---------|B     C|---------|D     E|---------|F      |
      |       |         |       |         |       |         |       |
      +-------+         +-------+         +-------+         +-------+
       (T)PE1            (S)PE2            (S)PE3            (T)PE4


                       Pseudowire Maintenance Points

   For example, suppose that in the above figure all of the nodes have
   Global_ID GID1; the node are represented as named in the figure; and
   The identification for the Pseudowire is:

           AGI            = AGI1
           East-Global_ID = GID1
           East-Node_ID   = PE1
           East-AC_ID     = AII1
           West-Global_ID = GID1
           West-Node_ID   = PE4
           West-AC_ID     = AII4

   The MEP_ID at point A would be -

   AGI1::GID1::PE1::AII1

   The PW_SE_ID at point C would be -

   AGI1::GID1::PE1::AII1::GID1::PE2

7.3.  MIP Identifiers

   At a cross-connect point, in order to automatically generate MIP_IDs
   for MPLS-TP, we simply use the IF_IDs of the two interfaces which are
   cross-connected via the label bindings of the MPLS-TP LSP.  This



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   allows, two MIPs to be independently identified in one node where a
   per-interface MIP model is used.  If only a per node MIP model is
   used then one MIP is configured.  In this case the MIP_ID is formed
   using the Node_ID and an IF_Num of 0.


8.  IANA Considerations

   There are no IANA actions resulting from this document.


9.  Security Considerations

   This document describes an information model and, as such, does not
   introduce security concerns.  Protocol specifications that describe
   use of this information model - however - may introduce security
   risks and concerns about authentication of participants.  For this
   reason, the writers of protocol specifications for the purpose of
   describing implementation of this information model need to describe
   security and authentication concerns that may be raised by the
   particular mechanisms defined and how those concerns may be
   addressed.


10.  References

10.1.  Normative References

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

   [2]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G.
        Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
        RFC 3209, December 2001.

   [3]  Metz, C., Martini, L., Balus, F., and J. Sugimoto, "Attachment
        Individual Identifier (AII) Types for Aggregation", RFC 5003,
        September 2007.

   [4]  Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS)
        Signaling Functional Description", RFC 3471, January 2003.

   [5]  Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS)
        Signaling Resource ReserVation Protocol-Traffic Engineering
        (RSVP-TE) Extensions", RFC 3473, January 2003.

   [6]  Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron,
        "Pseudowire Setup and Maintenance Using the Label Distribution



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        Protocol (LDP)", RFC 4447, April 2006.

10.2.  Informative References

   [7]  Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S.
        Ueno, "Requirements of an MPLS Transport Profile", RFC 5654,
        September 2009.


Authors' Addresses

   Matthew Bocci
   Alcatel-Lucent
   Voyager Place, Shoppenhangers Road
   Maidenhead, Berks  SL6 2PJ
   UK

   Email: matthew.bocci@alcatel-lucent.com


   George Swallow
   Cisco

   Email: swallow@cisco.com


   Eric Gray
   Ericsson
   900 Chelmsford Street
   Lowell, Massachussetts  01851-8100

   Email: eric.gray@ericsson.com



















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