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rfc:rfc6370

Internet Engineering Task Force (IETF) M. Bocci Request for Comments: 6370 Alcatel-Lucent Category: Standards Track G. Swallow ISSN: 2070-1721 Cisco

                                                               E. Gray
                                                              Ericsson
                                                        September 2011
            MPLS Transport Profile (MPLS-TP) Identifiers

Abstract

 This document specifies an initial set of identifiers to be used in
 the Transport Profile of Multiprotocol Label Switching (MPLS-TP).
 The MPLS-TP requirements (RFC 5654) 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 Operations,
 Administration, and Maintenance (OAM) functions compatible with IP/
 MPLS conventions.
 This document is a product of a joint Internet Engineering Task Force
 (IETF) / International Telecommunication Union Telecommunication
 Standardization Sector (ITU-T) effort to include an MPLS Transport
 Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
 (PWE3) architectures to support the capabilities and functionalities
 of a packet transport network as defined by the ITU-T.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6370.

Bocci, et al. Standards Track [Page 1] RFC 6370 MPLS-TP Identifiers September 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
 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 .....................................4
 2. Named Entities ..................................................5
 3. Uniquely Identifying an Operator - the Global_ID ................5
 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 ....................................9
         5.2.1. MPLS-TP Co-Routed Bidirectional LSP Identifiers .....9
         5.2.2. MPLS-TP Associated Bidirectional LSP Identifiers ....9
    5.3. Mapping to RSVP Signaling .................................10
 6. Pseudowire Path Identifiers ....................................11
 7. Maintenance Identifiers ........................................13
    7.1. Maintenance Entity Group Identifiers ......................13
         7.1.1. MPLS-TP Section MEG_IDs ............................13
         7.1.2. MPLS-TP LSP MEG_IDs ................................13
         7.1.3. Pseudowire MEG_IDs .................................14
    7.2. Maintenance Entity Group End Point Identifiers ............14
         7.2.1. MPLS-TP Section MEP_IDs ............................14
         7.2.2. MPLS-TP LSP_MEP_ID .................................15
         7.2.3. MEP_IDs for Pseudowires ............................15
    7.3. Maintenance Entity Group Intermediate Point Identifiers ...15
 8. Security Considerations ........................................15
 9. References .....................................................16
    9.1. Normative References ......................................16
    9.2. Informative References ....................................17

Bocci, et al. Standards Track [Page 2] RFC 6370 MPLS-TP Identifiers September 2011

1. Introduction

 This document specifies an initial set of identifiers to be used in
 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
 compatible with IP/MPLS conventions.  That is, the identifiers have
 been chosen to be compatible with existing IP, MPLS, GMPLS, and
 Pseudowire definitions.
 This document is a product of a joint Internet Engineering Task Force
 (IETF) / International Telecommunication Union Telecommunication
 Standardization Sector (ITU-T) effort to include an MPLS Transport
 Profile within the IETF MPLS and Pseudowire Emulation Edge-to-Edge
 (PWE3) architectures to support the capabilities and functionalities
 of a packet transport network as defined by the ITU-T.

1.1. Terminology

 AGI: Attachment Group Identifier
 AII: Attachment Interface Identifier
 AS: Autonomous System
 ASN: Autonomous System Number
 EGP: Exterior Gateway Protocol
 FEC: Forwarding Equivalence Class
 GMPLS: Generalized Multiprotocol Label Switching
 IGP: Interior Gateway Protocol
 LSP: Label Switched Path
 LSR: Label Switching Router
 MEG: Maintenance Entity Group
 MEP: Maintenance Entity Group End Point
 MIP: Maintenance Entity Group Intermediate Point

Bocci, et al. Standards Track [Page 3] RFC 6370 MPLS-TP Identifiers September 2011

 MPLS: Multiprotocol Label Switching
 NNI: Network-to-Network Interface
 OAM: Operations, Administration, and Maintenance
 PW: Pseudowire
 RSVP: Resource Reservation Protocol
 RSVP-TE: RSVP Traffic Engineering
 SAII: Source AII
 SPME: Sub-Path Maintenance Entity
 T-PE: Terminating Provider Edge
 TAII: Target AII

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

 All multiple-word atomic identifiers use underscores (_) between the
 words to join the words.  Many of the identifiers are composed of a
 set of other identifiers.  These are expressed by listing the latter
 identifiers joined with 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, A1-Node_ID is the Node_ID of
 a node referred to as A1.
 The notation defines a preferred ordering of the fields.
 Specifically, the designation A1 is used to indicate the lower sort
 order of a field or set of fields and Z9 is used to indicate the
 higher sort order of the same.  The sort is either alphanumeric or
 numeric depending on the field's definition.  Where the sort applies
 to a group of fields, those fields are grouped with {...}.
 Note, however, that the uniqueness of an identifier does not depend
 on the ordering, but rather, upon the uniqueness and scoping of the
 fields that compose the identifier.  Further, the preferred ordering

Bocci, et al. Standards Track [Page 4] RFC 6370 MPLS-TP Identifiers September 2011

 is not intended to constrain protocol designs by dictating a
 particular field sequence (for example, see Section 5.2.1) or even
 what fields appear in which objects (for example, see Section 5.3).

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 following entities are defined
 in this document:
  • Global_ID
  • Node
  • Interface
  • Tunnel
  • LSP
  • PW
  • MEG
  • MEP
  • MIP
 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 - the Global_ID

 The Global_ID is defined to uniquely identify an operator.  RFC 5003
 [3] defines a globally unique Attachment Interface Identifier (AII).
 That AII is composed of three parts: a Global_ID that uniquely
 identifies an operator, a prefix, and, finally, an 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
    provider's Autonomous System Number (ASN).  It is expected that
    the global ID will be derived from the globally unique ASN of the

Bocci, et al. Standards Track [Page 5] RFC 6370 MPLS-TP Identifiers September 2011

    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.
 A Global_ID is an unsigned 32-bit value and MUST be derived from a
 4-octet AS number assigned to the operator.  Note that 2-octet AS
 numbers have been incorporated in the 4-octet by placing the 2-octet
 AS number in the low-order octets and setting the two high-order
 octets to zero.
 ASN 0 is reserved and cannot be assigned to an operator.  An
 identifier containing a Global_ID of zero means that no Global_ID is
 specified.  Note that a Global_ID of zero is limited to entities
 contained within a single operator and MUST NOT be used across an
 NNI.
 The Global_ID is used solely to provide a globally unique context for
 other MPLS-TP identifiers.  While the AS number used in the Global_ID
 MUST be one that the operator is entitled to use, the use of the
 Global_ID is not related to the use of the ASN in protocols such as
 BGP.

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
 (sub-)layer, e.g., 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 a 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 EGP.  Where IPv6 addresses are used exclusively, a
 32-bit value unique within the scope of a Global_ID is assigned.
 An 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 an intermediate point 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
 Global_ID.

Bocci, et al. Standards Track [Page 6] RFC 6370 MPLS-TP Identifiers September 2011

 The term "interface" is used for the attachment point to an MPLS-TP
 section.  Within the context of a particular node, we call the
 identifier associated with an interface an "Interface Number"
 (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 special meaning (see Section 7.3, MIP Identifiers)
 and MUST NOT be used to identify an MPLS-TP interface.
 Note that IF_Num has no relation with the ifNum object defined in RFC
 2863 [8].  Further, no mapping is mandated between IF_Num and ifIndex
 in RFC 2863.
 An "Interface Identifier" (IF_ID) identifies an interface uniquely
 within the context of a Global_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.  The
 GMPLS signaling functional description [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 Global_ID.
 Note that MPLS-TP supports hierarchical sections.  The attachment
 point to an MPLS-TP section at any (sub-)layer requires a node-unique
 IF_Num.

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 Identifier" (Tunnel_ID)
 identifies the transport service and provides a stable binding to the
 client in the face of changes in the data-plane LSPs used to provide
 the service due to protection or restoration events.  This section
 defines an MPLS-TP Tunnel_ID to uniquely identify a tunnel, and an
 MPLS-TP LSP Identifier (LSP_ID) to uniquely identify an LSP
 associated with a tunnel.

Bocci, et al. Standards Track [Page 7] RFC 6370 MPLS-TP Identifiers September 2011

 For the case where multiple LSPs (for example) are used to support a
 single service with a common set of end points, using the Tunnel_ID
 allows for a trivial mapping between the server and client layers,
 providing a common service identifier that 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 unprotected)
 that may appear to the client as a single service attachment point.
 Keeping the Tunnel_ID consistent across working and protection LSPs
 is a useful construct currently employed within GMPLS.  However, the
 Tunnel_ID for a protection LSP MAY differ from that used by its
 corresponding working LSP.

5.1. MPLS-TP Point-to-Point Tunnel Identifiers

 At each end point, a tunnel is uniquely identified by the end point's
 Node_ID and a locally assigned tunnel number.  Specifically, a
 "Tunnel Number" (Tunnel_Num) is a 16-bit unsigned integer unique
 within the context of the Node_ID.  The motivation for each end point
 having its own tunnel number is to allow a compact form for the
 MEP_ID.  See Section 7.2.2.
 Having two tunnel numbers also serves to simplify other signaling
 (e.g., setup of associated bidirectional tunnels as described in
 Section 5.3).
 The concatenation of the two end point identifiers serves as the full
 identifier.  Using the A1/Z9 convention, the format of a Tunnel_ID
 is:
    A1-{Node_ID::Tunnel_Num}::Z9-{Node_ID::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:
    A1-{Global_ID::Node_ID::Tunnel_Num}::Z9-{Global_ID::Node_ID::
    Tunnel_Num}
 When an MPLS-TP Tunnel is configured, it MUST be assigned a unique
 IF_ID at each end point.  As usual, the IF_ID is composed of the
 local Node_ID concatenated with a 32-bit IF_Num.

Bocci, et al. Standards Track [Page 8] RFC 6370 MPLS-TP Identifiers September 2011

5.2. MPLS-TP LSP Identifiers

 This section defines identifiers for MPLS-TP co-routed bidirectional
 and associated bidirectional LSPs.  Note that MPLS-TP Sub-Path
 Maintenance Entities (SPMEs), as defined in RFC 5921 [9], are also
 LSPs and use these same forms of identifiers.

5.2.1. MPLS-TP Co-Routed Bidirectional LSP Identifiers

 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 Number (LSP_Num) is a 16-bit unsigned integer unique within
 the Tunnel_ID.  Thus, the format of an MPLS-TP co-routed
 bidirectional LSP_ID is:
    A1-{Node_ID::Tunnel_Num}::Z9-{Node_ID::Tunnel_Num}::LSP_Num
 Note that the uniqueness of identifiers does not depend on the A1/Z9
 sort ordering.  Thus, the identifier:
    Z9-{Node_ID::Tunnel_Num}::A1-{Node_ID::Tunnel_Num}::LSP_Num
 is synonymous with the one above.
 At the data-plane level, a co-routed bidirectional LSP is composed of
 two unidirectional LSPs traversing the same links in opposite
 directions.  Since a co-routed bidirectional LSP is provisioned or
 signaled as a single entity, a single LSP_Num is used for both
 unidirectional LSPs.  The unidirectional LSPs can be referenced by
 the identifiers:
    A1-Node_ID::A1-Tunnel_Num::LSP_Num::Z9-Node_ID and
    Z9-Node_ID::Z9-Tunnel_Num::LSP_Num::A1-Node_ID, respectively.
 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:
    A1-{Global_ID::Node_ID::Tunnel_Num}::Z9-{Global_ID::
    Node_ID::Tunnel_Num}::LSP_Num

5.2.2. MPLS-TP Associated Bidirectional LSP Identifiers

 For an associated bidirectional LSP, each of the unidirectional LSPs
 from A1 to Z9 and Z9 to A1 require LSP_Nums.  Each unidirectional LSP
 is uniquely identified by a single LSP number within the scope of the
 ingress's Tunnel_Num.  Specifically, an "LSP Number" (LSP_Num) is a

Bocci, et al. Standards Track [Page 9] RFC 6370 MPLS-TP Identifiers September 2011

 16-bit unsigned integer unique within the scope of the ingress's
 Tunnel_Num.  Thus, the format of an MPLS-TP associated bidirectional
 LSP_ID is:
    A1-{Node_ID::Tunnel_Num::LSP_Num}::
    Z9-{Node_ID::Tunnel_Num::LSP_Num}
 At the data-plane level, an associated bidirectional LSP is composed
 of two unidirectional LSPs between two nodes in opposite directions.
 The unidirectional LSPs may be referenced by the identifiers:
    A1-Node_ID::A1-Tunnel_Num::A1-LSP_Num::Z9-Node_ID and
    Z9-Node_ID::Z9-Tunnel_Num::Z9-LSP_Num::A1-Node_ID, respectively.
 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:
    A1-{Global_ID::Node_ID::Tunnel_Num::LSP_Num}::
    Z9-{Global_ID::Node_ID::Tunnel_Num::LSP_Num}

5.3. Mapping to RSVP Signaling

 This section is informative and exists to help understand the
 structure of the LSP IDs.
 GMPLS [5] is based on RSVP-TE [2].  This section defines the mapping
 from an MPLS-TP LSP_ID to RSVP-TE.  At this time, RSVP-TE has yet to
 be extended to accommodate Global_IDs.  Thus, a mapping is only made
 for the network unique form of the LSP_ID and assumes that the
 operator has chosen to derive its Node_IDs from valid IPv4 addresses.
 GMPLS and RSVP-TE signaling use a 5-tuple to uniquely identify an LSP
 within an operator's network.  This tuple is composed of a Tunnel
 End-point Address, Tunnel_ID, Extended Tunnel ID, Tunnel Sender
 Address, and (RSVP) LSP_ID.  RFC 3209 allows some flexibility in how
 the Extended Tunnel ID is chosen, and a direct mapping is not
 mandated.  One convention that is often used, however, is to populate
 this field with the same value as the Tunnel Sender Address.  The
 examples below follow that convention.  Note that these are only
 examples.

Bocci, et al. Standards Track [Page 10] RFC 6370 MPLS-TP Identifiers September 2011

 For a co-routed bidirectional LSP signaled from A1 to Z9, the mapping
 to the GMPLS 5-tuple is as follows:
  • Tunnel End-point Address = Z9-Node_ID
  • Tunnel_ID = A1-Tunnel_Num
  • Extended Tunnel_ID = A1-Node_ID
  • Tunnel Sender Address = A1-Node_ID
  • (RSVP) LSP_ID = LSP_Num
 An associated bidirectional LSP between two nodes A1 and Z9 consists
 of two unidirectional LSPs, one from A1 to Z9 and one from Z9 to A1.
 In situations where a mapping to the RSVP-TE 5-tuples is required,
 the following mappings are used.  For the A1 to Z9 LSP, the mapping
 would be:
  • Tunnel End-point Address = Z9-Node_ID
  • Tunnel_ID = A1-Tunnel_Num
  • Extended Tunnel_ID = A1-Node_ID
  • Tunnel Sender Address = A1-Node_ID
  • (RSVP) LSP_ID = A1-LSP_Num
 Likewise, the Z9 to A1 LSP, the mapping would be:
  • Tunnel End-point Address = A1-Node_ID
  • Tunnel_ID = Z9-Tunnel_Num
  • Extended Tunnel_ID = Z9-Node_ID
  • Tunnel Sender Address = Z9-Node_ID
  • (RSVP) LSP_ID = Z9-LSP_Num

6. Pseudowire Path Identifiers

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

Bocci, et al. Standards Track [Page 11] RFC 6370 MPLS-TP Identifiers September 2011

 In an MPLS-TP environment, a PW is identified by a set of identifiers
 that can be mapped directly to the elements required by the
 Generalized PWid FEC (type 129) and AII Type 2.  To distinguish this
 identifier from other Pseudowire Identifiers, we call this a
 Pseudowire Path Identifier (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 Generalized PWid FEC (type 129), all that is required
 is an Attachment Group Identifier (AGI).  That field is exactly as
 specified in RFC 4447.  A (bidirectional) pseudowire consists of a
 pair of unidirectional LSPs, one in each direction.  Thus, for
 signaling, the Generalized PWid FEC (type 129) has a notion of Source
 AII (SAII) and Target AII (TAII).  These terms are used relative to
 the direction of the LSP, i.e., the SAII is assigned to the end that
 allocates the PW label for a given direction, and the TAII to the
 other end.
 In a purely configured environment, when referring to the entire PW,
 this distinction is not critical.  That is, a Generalized PWid FEC
 (type 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 end point, the AII associated with
 that end point comes first.  The complete PW_Path_ID is:
    AGI::A1-{Global_ID::Node_ID::AC_ID}::
    Z9-{Global_ID::Node_ID::AC_ID}.
 In a signaled environment the LSP from A1 to Z9 would be initiated
 with a label request from A1 to Z9 with the fields of the Generalized
 PWid FEC (type 129) completed as follows:
    AGI = AGI
    SAII = A1-{Global_ID::Node_ID::AC_ID}
    TAII = Z9-{Global_ID::Node_ID::AC_ID}
 The LSP from Z9 to A1 would signaled with:
    AGI = AGI
    SAII = Z9-{Global_ID::Node_ID::AC_ID}
    TAII = A1-{Global_ID::Node_ID::AC_ID}

Bocci, et al. Standards Track [Page 12] RFC 6370 MPLS-TP Identifiers September 2011

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 a Maintenance
 Entity Group End Point (MEP), a Maintenance Entity Group Intermediate
 Point (MIP), or a Pseudowire Segment End Point.  Within the context
 of a MEG, MEPs and MIPs must be uniquely identified.  This section
 defines a means of uniquely identifying Maintenance Entity Groups and
 Maintenance Entities.  It also uniquely defines 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 sections, LSPs, and Pseudowires.  The formats were chosen to
 follow the IP-compatible identifiers defined above.

7.1.1. MPLS-TP Section MEG_IDs

 MPLS-TP allows a hierarchy of sections.  See "MPLS-TP Data Plane
 Architecture" (RFC 5960 [10]).  Sections above layer 0 are MPLS-TP
 LSPs.  These use their MPLS-TP LSP MEG IDs defined in Section 7.1.2.
 IP-compatible MEG_IDs for MPLS-TP sections at layer 0 are formed by
 concatenating the two IF_IDs of the corresponding section using the
 A1/Z9 ordering.  For example:
    A1-IF_ID::Z9-IF_ID
 Where the Section_MEG_ID needs to be globally unique, this is
 accomplished by using globally unique Node_IDs as defined above.
 Thus, a globally unique Section_MEG_ID becomes:
    A1-{Global_ID::IF_ID}::Z9-{Global_ID::IF_ID}

7.1.2. MPLS-TP LSP MEG_IDs

 A MEG pertains to a unique MPLS-TP LSP.  IP compatible MEG_IDs for
 MPLS-TP LSPs are simply the corresponding LSP_IDs; however, the A1/Z9
 ordering MUST be used.  For bidirectional co-routed LSPs, the format
 of the LSP_ID is found in Section 5.2.1.  For associated
 bidirectional LSPs, the format is in Section 5.2.2.

Bocci, et al. Standards Track [Page 13] RFC 6370 MPLS-TP Identifiers September 2011

 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 an 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.

7.1.3. 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; however, the
 A1/Z9 ordering MUST be used.  The PW_Path_ID is described in
 Section 6.  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 are to be encoded in TLVs, different types need to be
 assigned for these two identifiers.

7.2. Maintenance Entity Group End Point Identifiers

7.2.1. MPLS-TP Section MEP_IDs

 IP-compatible MEP_IDs for MPLS-TP sections above layer 0 are their
 MPLS-TP LSP_MEP_IDs.  See Section 7.2.2.
 IP-compatible MEP_IDs for MPLS-TP sections at layer 0 are simply the
 IF_IDs of each end of the section.  For example, for a section whose
 MEG_ID is:
    A1-IF_ID::Z9-IF_ID
 the Section MEP_ID at A1 would be:
    A1-IF_ID
 and the Section MEP_ID at Z9 would be:
    Z9-IF_ID.
 Where the Section MEP_ID needs to be globally unique, this is
 accomplished by using globally unique Node_IDs as defined above.
 Thus, a globally unique Section MEP_ID becomes:
    Global_ID::IF_ID.

Bocci, et al. Standards Track [Page 14] RFC 6370 MPLS-TP Identifiers September 2011

7.2.2. 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 end point.  This
 ensures that MEP_IDs are unique for all LSPs within an 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
 co-routed bidirectional LSPs, the single LSP_Num is used at both
 ends.  In the case of associated bidirectional LSPs, the LSP_Num is
 the one unique to where the MEP resides.
 In situations where global uniqueness is required, this becomes:
    Global_ID::Node_ID::Tunnel_Num::LSP_Num

7.2.3. MEP_IDs for Pseudowires

 Like MPLS-TP LSPs, Pseudowire end points (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
 for a 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.

7.3. Maintenance Entity Group Intermediate Point Identifiers

 For a MIP that is associated with a particular interface, we simply
 use the IF_ID (see Section 4) of the interfaces that are cross-
 connected.  This allows 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. 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

Bocci, et al. Standards Track [Page 15] RFC 6370 MPLS-TP Identifiers September 2011

 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.
 Uniqueness of the identifiers from this document is guaranteed by the
 assigner (e.g., a Global_ID is unique based on the assignment of ASNs
 from IANA and both a Node_ID and an IF_Num are unique based on the
 assignment by an operator).  Failure by an assigner to use unique
 values within the specified scoping for any of the identifiers
 defined herein could result in operational problems.  For example, a
 non-unique MEP value could result in failure to detect a mis-merged
 LSP.
 Protocol specifications that utilize the identifiers defined herein
 need to consider the implications of guessable identifiers and, where
 there is a security implication, SHOULD give advice on how to make
 identifiers less guessable.

9. References

9.1. 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
       Protocol (LDP)", RFC 4447, April 2006.

Bocci, et al. Standards Track [Page 16] RFC 6370 MPLS-TP Identifiers September 2011

9.2. 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.
 [8]   McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
       RFC 2863, June 2000.
 [9]   Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. Berger, "A
       Framework for MPLS in Transport Networks", RFC 5921, July 2010.
 [10]  Frost, D., Bryant, S., and M. Bocci, "MPLS Transport Profile
       Data Plane Architecture", RFC 5960, August 2010.

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

Bocci, et al. Standards Track [Page 17]

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