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Versions: (draft-zhao-mpls-ldp-multi-topology) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7307

Internet Engineering Task Force                                  Q. Zhao
Internet-Draft                                         Huawei Technology
Intended status: Standards Track                                 K. Raza
Expires: August, 2014                                            C. Zhou
                                                           Cisco Systems
                                                                 L. Fang
                                                               Microsoft
                                                                   L. Li
                                                            China Mobile
                                                                 D. King
                                                      Old Dog Consulting
                                                       February 14, 2014


                   LDP Extensions for Multi Topology
               draft-ietf-mpls-ldp-multi-topology-11.txt

Abstract

   Multi-Topology (MT) routing is supported in IP networks with the use
   of MT aware IGPs.  In order to provide MT routing within
   Multiprotocol Label Switching (MPLS) Label Distribution Protocol
   (LDP) networks new extensions are required.

   This document describes the LDP protocol extensions required to
   support MT routing in an MPLS environment.

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 August, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .4
   3.  Signaling Extensions . . . . . . . . . . . . . . . . . . . . .4
     3.1.  Topology-Scoped Forwarding Equivalence Class (FEC) . . . .4
     3.2.  New Address Families: MT IP  . . . . . . . . . . . . . . .4
     3.3.  LDP FEC Elements with MT IP AF . . . . . . . . . . . . . .5
     3.4.  IGP MT-ID Mapping and Translation  . . . . . . . . . . . .6
     3.5.  LDP MT Capability Advertisement  . . . . . . . . . . . . .6
       3.5.1.  Protocol Extension . . . . . . . . . . . . . . . . . .6
       3.5.2.  Procedures . . . . . . . . . . . . . . . . . . . . . .7
     3.6.  LDP Sessions . . . . . . . . . . . . . . . . . . . . . . .8
     3.7.  Reserved MT ID Values  . . . . . . . . . . . . . . . . . .8
   4.  MT Applicability on FEC-based features . . . . . . . . . . . .9
     4.1.  Typed Wildcard FEC Element . . . . . . . . . . . . . . . .9
     4.2.  End-of-LIB . . . . . . . . . . . . . . . . . . . . . . . .9
     4.3.  LSP Ping . . . . . . . . . . . . . . . . . . . . . . . . .9
       4.3.1.  New FEC Sub-Types  . . . . . . . . . . . . . . . . . .10
       4.3.2.  MT LDP IPv4 FEC Sub-TLV  . . . . . . . . . . . . . . .10
       4.3.3.  MT LDP IPv6 FEC Sub-TLV  . . . . . . . . . . . . . . .11
       4.3.4.  Operation Considerations . . . . . . . . . . . . . . .11
   5.  Error Handling . . . . . . . . . . . . . . . . . . . . . . . .11
     5.1.  MT Error Notification for Invalid Topology ID  . . . . . .12
   6.  Backwards Compatibility  . . . . . . . . . . . . . . . . . . .12
   7.  MPLS Forwarding in MT  . . . . . . . . . . . . . . . . . . . .12


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   8.  Security Consideration . . . . . . . . . . . . . . . . . . . .12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .13
   10. Manageability Considerations . . . . . . . . . . . . . . . . .14
     10.1. Control of Function and Policy . . . . . . . . . . . . . .14
     10.2. Information and Data Models  . . . . . . . . . . . . . . .14
     10.3. Liveness Detection and Monitoring  . . . . . . . . . . . .14
     10.4. Verify Correct Operations  . . . . . . . . . . . . . . . .14
     10.5. Requirements On Other Protocols  . . . . . . . . . . . . .15
     10.6. Impact On Network Operations . . . . . . . . . . . . . . .15
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . .15
   12. Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . .16
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . .16
     13.1. Normative References . . . . . . . . . . . . . . . . . . .16
     13.2. Informative References . . . . . . . . . . . . . . . . . .17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .17


1.  Introduction

   Multi-Topology (MT) routing is supported in IP networks with the use
   of MT aware IGPs.  It would be advantageous for communications
   Service Providers (CSP) to support Multiple Topologies (MT) within
   MPLS environments (MPLS-MT).  The benefits of MPLS-MT enabled
   networks include:

   o  A CSP may want to assign varying Quality of Service (QoS) profiles
      to traffic, based on a specific MT.

   o  Separate routing and MPLS domains may be used to isolate multicast
      and IPv6 islands within the backbone network.

   o  Specific IP address space could be routed across an MT based on
      security or operational isolation requirements.

   o  Low latency links could be assigned to an MT for delay sensitive
      traffic.

   o  Management traffic could be separated from customer traffic using
      multiple MTs, where the management traffic MT does not use links
      that carry customer traffic.

   This document describes the Label Distribution Protocol (LDP)
   procedures and protocol extensions required to support MT routing in
   an MPLS environment.

   This document also updates RFC4379 by defining two new FEC types for
   Label Switched Path (LSP) ping.




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2.  Terminology

   This document uses MPLS terminology defined in [RFC5036].  Additional
   terms are defined below:

   o  MT-ID: A 16 bit value used to represent the Multi-Topology ID.

   o  Default MT Topology: A topology that is built using the MT-ID
      default value of 0.

   o  MT Topology: A topology that is built using the corresponding
      MT-ID.

   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 [RFC2119].


3.  Signaling Extensions

3.1.  Topology-Scoped Forwarding Equivalence Class (FEC)

   LDP assigns and binds a label to a Forwarding Equivalence Class
   (FEC), where a FEC is a list of one or more FEC elements.  To setup
   LSPs for unicast IP routing paths, LDP assigns local labels for IP
   prefixes, and advertises these labels to its peers so that an LSP is
   setup along the routing path.  To setup MT LSPs for IP prefixes under
   a given topology scope, the LDP "prefix-related" FEC element must be
   extended to include topology information.  This implies that MT-ID
   becomes an attribute of Prefix-related FEC element, and all FEC-Label
   binding operations are performed under the context of given topology
   (MT-ID).

   The following Subsection 3.2(New Address Families (AF): MT IP)
   defines the extension required to bind "prefix-related" FEC to a
   topology.

3.2.  New Address Families: MT IP

   The LDP base specification [RFC5036] (Section 4.1) defines the
   "Prefix" FEC Element.  The "Prefix" encoding is defined for a given
   "Address Family" (AF), and has length (in bits) specified by the
   "PreLen" field.

   To extend IP address families for MT, two new Address Families named
   "MT IP" and "MT IPv6" are used to specify IPv4 and IPv6 prefixes
   within a topology scope.

   The format of data associated with these new Address Families is
   described below:

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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     IP Address                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Reserved             |        MT-ID                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: MT IP Address Family Format

   Where "IP Address" is an IPv4 and IPv6 address/prefix for "MT IP" and
   "MT IPv6" AF respectively, and the field "MT-ID" corresponds to 16-
   bit Topology ID for given address.

   The definition and usage of the rest fields in the FEC Elements are
   same as defined for IP/IPv6 AF.  The value of MT-ID 0 corresponds to
   default topology and MUST be ignored on receipt so as to not cause
   any conflict/confusion with existing non-MT procedures.

   The defined FEC Elements with "MT IP" Address Family can be used in
   any LDP message and procedures that currently specify and allow the
   use of FEC Elements with IP/IPv6 Address Family.

3.3.  LDP FEC Elements with MT IP AF

   The following section specifies the format extensions of the existing
   LDP FEC Elements to support MT.  The "Address Family" of these FEC
   elements will be set to "MT IP" or "MT IPv6".

   The MT Prefix FEC element encoding is as follows:


      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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Prefix (2)   | Address Family (MT IP/MT IPv6)|     PreLen    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Prefix                                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Reserved             |        MT-ID                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: MT Prefix FEC Element Format

   The MT Typed Wildcard FEC element encoding is as follows:






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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Typed Wcard (5)|    FEC Type   |   Len = 6     |  AF = MT IP ..|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |... or MT IPv6 |         MT ID                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: MT Typed Wildcard FEC Element

   The above format can be used for any LDP FEC Element that allows use
   of IP/IPv6 address family.  In the scope of this document, the
   allowed "FEC Type" in a MT Typed Wildcard FEC Element is "Prefix" FEC
   element.

3.4.  IGP MT-ID Mapping and Translation

   The non-reserved non-special IGP MT-ID values can be used and carried
   in LDP without the need for translation.  However, there is a need
   for translating reserved or special IGP MT-ID values to corresponding
   LDP MT-IDs.  The assigned, unassigned and special LDP MT-ID values
   are requested In Section 9.  (IANA Considerations).

   How future LDP MT-ID values are allocated are out of of scope of this
   document.  Instead a new Internet-Draft will be created to document
   the allocation policy and process for requesting new MT-ID values.

3.5.  LDP MT Capability Advertisement

3.5.1.  Protocol Extension

   We specify a new LDP capability, named "Multi-Topology (MT)", which
   is defined in accordance with LDP Capability definition guidelines
   [RFC5561].  The LDP "MT" capability can be advertised by an LDP
   speaker to its peers either during the LDP session initialization or
   after the LDP session is setup to announce LSR capability to support
   MT for the given IP address family.  An LDP speaker MUST NOT send
   messages containing MT FEC elements unless the peer has said it can
   handle it.

   The MT capability is specified using "Multi-Topology Capability" TLV.
   The "Multi-Topology Capability" TLV format is in accordance with LDP
   capability guidelines as defined in [RFC5561].  To be able to specify
   IP address family, the capability specific data (i.e.  "Capability
   Data" field of Capability TLV) is populated using "Typed Wildcard FEC
   Element" as defined in [RFC5918].

   The format of "Multi-Topology Capability" TLV is as follows:


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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |U|F| Multi-Topology Cap.(IANA) |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |S| Reserved    |                                               |
    +-+-+-+-+-+-+-+-+                                               |
    ~                Typed Wildcard FEC element(s)                  ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 4: Multi-Topology Capability TLV Format

   Where:


   o  U- and F-bits: MUST be 1 and 0, respectively, as per Section 3.
      (Signaling Extensions) of LDP Capabilities [RFC5561].

   o  Multi-Topology Capability: Capability TLV type (IANA assigned)

   o  S-bit: MUST be 1 if used in LDP "Initialization" message.  MAY be
      set to 0 or 1 in dynamic "Capability" message to advertise or
      withdraw the capability respectively.

   o  Typed Wildcard FEC element(s): One or more elements specified as
      the "Capability data".

   o  Length: length of Value field, starting from S bit, in octets.

   o  The encoding of Typed Wildcard FEC element, as defined in
      [RFC5918], is defined in the section 3.3 (Typed Wildcard FEC
      Element) of this document.  The MT-ID field of MT Typed Wildcard
      FEC Element MUST be set to "Wildcard Topology" when it is
      specified in MT Capability TLV.

3.5.2.  Procedures

   To announce its MT capability for an IP address family, LDP FEC type,
   and Multi Topology, an LDP speaker sends an "MT Capability" including
   the exact Typed Wildcard FEC element with corresponding
   "AddressFamily" field (i.e., set to "MT IP" for IPv4 and set to "MT
   IPv6" for IPv6 address family), corresponding "FEC Type" field (i.e.,
   set to "Prefix"), and corresponding "MT-ID".  To announce its MT
   capability for both IPv4 and IPv6 address family, or for multiple FEC
   types, or for multiple Multi Topologies, an LDP speaker sends "MT
   Capability" with one or more MT Typed FEC elements in it.

   o  The capability for supporting multi-topology in LDP can be


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      advertised during LDP session initialization stage by including
      the LDP MT capability TLV in LDP Initialization message.  After an
      LDP session is established, the MT capability can also be
      advertised or withdrawn using Capability message (only if "Dynamic
      Announcement" capability [RFC5561] has already been successfully
      negotiated).

   o  If an LSR has not advertised MT capability, its peer MUST NOT send
      any LDP messages with FEC elements that include MT identifier to
      this LSR.

   o  If an LSR is changed from non-MT capable to MT capable, it sets
      the S bit in MT capability TLV and advertises via the Capability
      message (if it supports Dynamic Announcement Capability).  The
      existing LSP is treated as LSP for default MT (ID 0).

   o  o If an LSR is changed from LDP-MT capable to non-MT capable, it
      initiates withdraw of all label mapping for existing LSPs of all
      non-default MTs.  It also cleans up all the LSPs of all non-
      default MTs locally.  Then it clears the S bit in MT capability
      TLV and advertises via the Capability message (if it supports
      Dynamic Announcement Capability).  When an LSR knows the peer node
      is changed from LDP-MT capable to non-MT capable, it cleanup all
      the LSPs of all non-default MTs locally and initiate withdraw of
      all label mapping for existing LSPs of all non-default MTs.  Both
      sides of the nodes send label release to its peer once they
      receive the label release messages even both sides have already
      cleaned up all the LSPs locally.

   o  If an LSR does not support "Dynamic Announcement Capability", it
      MUST reset session with its peer whenever LSR changes its local
      capability with regards to supporting LDP MT.

   o  If an LSR is changed from IGP-MT capable to non-MT capable, it may
      wait until the routes update to withdraw FEC and release the label
      mapping for existing LSPs of specific MT.

3.6.  LDP Sessions

   Since using different label spaces for different topologies would
   imply significant changes to the data plane, a single global label
   space is supported in this solution.  There will be one session
   supported between a pair of peers, even if there are multiple
   topologies supported between these two peers.

3.7.  Reserved MT ID Values

   Certain MT topologies are assigned to serve predetermined purposes.



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   In Section 9.  (IANA Considerations), this document defines a new
   IANA registry "LDP Multi-Topology ID Name Space" under IANA "LDP
   Parameter" namespace to keep an LDP MT-ID reserved value.

   If an LSR receives a FEC element with an "MT-ID" value that is
   "Reserved" for future use (and not IANA allocated yet), the LSR MUST
   abort the processing of the FEC element, and SHOULD send a
   notification message with status code "Invalid Topology ID" to the
   sender.


4.  MT Applicability on FEC-based features

4.1.  Typed Wildcard FEC Element

   [RFC5918] extends base LDP and defines Typed Wildcard FEC Element
   framework.  Typed Wildcard FEC element can be used in any LDP message
   to specify a wildcard operation/action for given type of FEC.

   The MT extensions defined in document do not require any extension to
   procedures for Typed Wildcard FEC element, and these procedures apply
   as-is to MT wildcarding.  The MT extensions, though, allow use of "MT
   IP" or "MT IPv6" in the Address Family field of the Typed Wildcard
   FEC element in order to use wildcard operations in the context of a
   given topology.  The use of MT-scoped address family also allows us
   to specify MT-ID in these operations.

   The defined format in Section 3.3 (Typed Wildcard FEC Element) allows
   an LSR to perform wildcard FEC operations under the scope of a
   topology.  If an LSR wishes to perform wildcard operation that
   applies to all topologies, it can use a "Wildcard Topology" MT-ID.
   For example, upon local de-configuration of a topology "x", an LSR
   may send a typed wildcard label withdraw message with MT-ID "x" to
   withdraw all its labels from the peer that advertised under the scope
   of topology "x".  Additionally, upon a global configuration change,
   an LSR may send a typed wildcard label withdraw message with the
   MT-ID set to "Wildcard Topology" to withdraw all its labels under all
   topologies from the peer.

4.2.  End-of-LIB

   [RFC5919] specifies extensions and procedures for an LDP speaker to
   signal its convergence for a given FEC type towards a peer.  The
   procedures defined in [RFC5919] applies as-is to an MT FEC element.
   This allows an LDP speaker to signal its IP convergence using Typed
   Wildcard FEC element, and its MT IP convergence per topology using a
   MT Typed Wildcard FEC element.

4.3.  LSP Ping


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   [RFC4379] defines procedures to detect data-plane failures in MPLS
   LSPs via LSP ping.  That specification defines a "Target FEC Stack"
   TLV that describes the FEC stack being tested.  This TLV is sent in
   an MPLS echo request message towards LSPs egress LSR, and is
   forwarded along the same data path as other packets belonging to the
   FEC.

   "Target FEC Stack" TLV contains one or more sub-TLVs pertaining to
   different FEC types.  Section 3.2 of [RFC4379] defines Sub-Types and
   format for the FEC.  To support LSP ping for MT LDP LSPs, this
   document defines following extensions to [RFC4379].


4.3.1.  New FEC Sub-Types

   We define two new FEC types for LSP ping:

   o  MT LDP IPv4 FEC

   o  MT LDP IPv6 FEC

   We also define following new sub-types for sub-TLVs to specify these
   FECs in the "Target FEC Stack" TLV of [RFC4379]:


         Sub-Type       Length            Value Field
         --------       ------            -----------------
             TBA5            8            MT LDP IPv4 prefix
             TBA6           20            MT LDP IPv6 prefix

                   Figure 5: new sub-types for sub-TLVs

   The rules and procedures of using these sub-TLVs in an MPLS echo
   request message are same as defined for LDP IPv4/IPv6 FEC sub-TLV
   types in [RFC4379].

4.3.2.  MT LDP IPv4 FEC Sub-TLV

   The format of "MT LDP IPv4 FEC" sub-TLV to be used in a "Target FEC
   Stack" [RFC4379] is:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Type = TBA5(MT LDP IPv4 FEC) |          Length = 8           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          IPv4 prefix                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Prefix Length |      MBZ      |       MT-ID                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                     Figure 6: MT LDP IPv4 FEC sub-TLV

   The format of this sub-TLV is similar to LDP IPv4 FEC sub-TLV as
   defined in [RFC4379].  In addition to "IPv4 prefix" and "Prefix
   Length" fields, this new sub-TLV also specifies MT-ID (Multi-Topology
   ID).  The Length for this sub-TLV is 5.


4.3.3.  MT LDP IPv6 FEC Sub-TLV

   The format of "MT LDP IPv6 FEC" sub-TLV to be used in a "Target FEC
   Stack" [RFC4379] is:


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Type = TBA6(MT LDP IPv6 FEC) |          Length = 20          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                          IPv6 prefix                          |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Prefix Length |     MBZ       |       MT-ID                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 7: MT LDP IPv6 FEC sub-TLV

   The format of this sub-TLV is similar to LDP IPv6 FEC sub-TLV as
   defined in [RFC4379].  In addition to "IPv6 prefix" and "Prefix
   Length" fields, this new sub-TLV also specifies MT-ID (Multi-Topology
   ID).  The Length for this sub-TLV is 17.

4.3.4.  Operation Considerations

   To detect data plane failures using LSP Ping for a specific topology,
   the router will initiate an LSP Ping request with the target FEC
   stack TLV containing LDP MT IP Prefix Sub-TLV in the Echo Request
   packet.  The Echo Request packet is sent with the label bound to the
   IP Prefix in the topology.  Once the echo request packet reaches the
   target router, it will process the packet and perform checks for the
   LDP MT IP Prefix sub-TLV present in the Target FEC Stack as described
   in [RFC4379] and respond according to [RFC4379] processing rules.
   For the case that the LSP ping with return path is not specified, the
   reply packet must go through the default topology instead of the
   topology where the Echo Request goes through.


5.  Error Handling

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   The extensions defined in this document utilize the existing LDP
   error handling defined in [RFC5036].  If an LSR receives an error
   notification from a peer for a session, it terminates the LDP session
   by closing the TCP transport connection for the session and
   discarding all multi-topology label mappings learned via the session.



5.1.  MT Error Notification for Invalid Topology ID

   An LSR should respond with an "Invalid Topology ID" status code in
   LDP Notification message when it receives an LDP message with a FEC
   element specifying an MT-ID which is not locally known or not
   supported.  The LSR MUST also discard the entire message before
   sending the Notification.


6.  Backwards Compatibility

   The MPLS-MT solution is backwards compatible with existing LDP
   enhancements defined in [RFC5036], including message authenticity,
   integrity of message, and topology loop detection.

   The legacy node which does not support MT should not receive any MT
   related LDP messages.  In case the bad things happen, according to
   [RFC5036], processing of such messages should be aborted.


7.  MPLS Forwarding in MT

   Although forwarding is out of the scope of this draft, we include
   some forwarding consideration for informational purpose here.

   The specified signaling mechanisms allow all the topologies to share
   the platform-specific label space, This feature allows the existing
   data plane techniques to be used.  Also, there is no way for the data
   plane to associate a received packet with any one topology, meaning
   that topology-specific label spaces cannot be used.


8.  Security Consideration

   The use of MT over existing MPLS solutions does not offer any
   specific security benefit.

   General LDP Communication security threats and how these may be
   mitigated are described in [RFC5036], these threats include:

   o  Spoofing


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   o  Privacy

   o  Denial of Service

   For further discussion regarding possible LDP communication threats
   and mitigation techniques see [RFC5920].

9.  IANA Considerations

   The document introduces following new protocol elements that require
   IANA consideration and assignments:

   o  New LDP Capability TLV: "Multi-Topology Capability" TLV (requested
      code point: TBA1 from LDP registry "TLV Type Name Space").

   o  New Status Code: "Invalid Topology ID" (requested code point: TBA2
      from LDP registry "Status Code Name Space").


            Registry:
            Range/Value          Description
            --------------       ------------------------------
            TBA1                 Invalid Topology ID

        Figure 8: New Code Points for LDP Multi Topology Extensions


   o  New address families under IANA registry "Address Family Numbers":

     - MT IP: Multi-Topology IP version 4 (requested codepoint:26)
     - MT IPv6: Multi-Topology IP version 6 (requested codepoint:27)

                       Figure 9: Address Family Numbers


   o  New registry "MPLS Multi-Topology Identifiers". The allocation
      policies for this registry are:

        Range/Value  Purpose                                 Reference
        -----------  -------------------------------------  ----------
        0            Default/standard topology              [This.I-D]
        1            IPv4 in-band management                [This.I-D]
        2            IPv6 routing topology                  [This.I-D]
        3            IPv4 multicast topology                [This.I-D]
        4            IPv6 multicast topology                [This.I-D]
        5            IPv6 in-band management                [This.I-D]
        6-3995       Unassigned for future IGP topologies   [This.I-D]
                     Assigned by Standards Action           [This.I-D]
        3996-4095    Experimental                           [This.I-D]
        4096-65534   Unassigned for MPLS topologies         [This.I-D]
                     Assigned by Standards Action
        65535        Wildcard Topology                      [This.I-D]

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            Figure 10: MPLS Multi-Topology Identifier registry

   o  New Sub-TLV Types for LSP ping: Following new sub-type values
      under TLV type 1 (Target FEC Stack) from "Multi-Protocol Label
      Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
      registry, and "TLVs and sub-TLVs" sub-registry.



         Sub-Type      Value Field
         --------      -----------
             TBA3      MT LDP IPv4 prefix
             TBA4      MT LDP IPv6 prefix


                 Figure 11: New Sub-TLV Types for LSP ping

   IANA should allocate the next available numbers for these TBAs.

   As highlighted at the end of Section 3.4 (IGP MT-ID Mapping and
   Translation), a new Internet-Draft will be created to document the
   policy and process for allocating new MT-ID values.


10.  Manageability Considerations

10.1.  Control of Function and Policy

   There are capabilities that should be configurable to enable good
   manageability.  One such example is to allow enable or disable LDP
   Multi-Topology capability.  It is assumed that the mapping of the LDP
   MT ID and IGP MT ID is manually configured on every router by
   default.  If an automatic mapping between IGP MT IDs and LDP MT IDs
   is needed, there must be explicit configuration to do so.

10.2.  Information and Data Models

   Any extensions that may be required for existing MIBs are beyond the
   scope of this document.

10.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements.

10.4.  Verify Correct Operations



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   If an operator is trying to debug LDP MT enabled network and wants to
   make the association between the LDP label advertisement and the IGP
   routing advertisement, then the user MUST understand the mapping
   mechanism to convert the IGP MT ID to the LDP MT ID.  This type of
   mapping mechanisms is out of the scope of this document.

10.5.  Requirements On Other Protocols

   If the LDP MT ID has an implicit dependency on IGP MT ID, then the
   corresponding IGP MT feattures will need to be supported.

10.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on network
   operations.


11.  Contributors

         Ning So
         Tata Communications
         2613 Fairbourne Cir.
         Plano, TX  75082
         USA

         Email: ning.so@tatacommunications.com

         Raveendra Torvi
         Juniper Networks
         10, Technoogy Park Drive
         Westford, MA  01886-3140
         US

         Email: rtorvi@juniper.net

         Huaimo Chen
         Huawei Technology
         125 Nagog Technology Park
         Acton, MA  01719
         US

         Email: huaimochen@huawei.com

         Emily Chen
         2717 Seville Blvd, Apt 1205,
         Clearwater, FL 33764
         US

         Email: emily.chen220@gmail.com


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         Chen Li
         China Mobile
         53A, Xibianmennei Ave.
         Xunwu District, Beijing  01719
         China

         Email: lichenyj@chinamobile.com

         Lu Huang
         China Mobile
         53A, Xibianmennei Ave.
         Xunwu District, Beijing  01719
         China

         Email: huanglu@chinamobile.com

         Zhenbin Li
         Huawei Technology
         2330 Central Expressway
         Santa Clara, CA  95050
         US

         Email: zhenbin.li@huawei.com


12.  Acknowledgement

   The authors would like to thank Dan Tappan, Nabil Bitar, Huang Xin,
   Eric Rosen, IJsbrand Wijnands, Dimitri Papadimitriou, Yiqun Chai,
   Pranjal Dutta, George Swallow, Curtis Villamizar, Adrian Farrel, Alia
   Atlas, Loa Anderson, Joel Halpern and Kathleen Moriarty for their
   valuable comments on this draft.


13.  References

13.1.  Normative References

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

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5561]  Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
              Le Roux, "LDP Capabilities", RFC 5561, July 2009.

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   [RFC5918]  Asati, R., Minei, I., and B. Thomas, "Label Distribution
              Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
              (FEC)", RFC 5918, August 2010.

   [RFC5919]  Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
              "Signaling LDP Label Advertisement Completion", RFC 5919,
              August 2010.

13.2.  Informative References

   [RFC5920]  Fang, L., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.


Authors' Addresses

   Quintin Zhao
   Huawei Technology
   125 Nagog Technology Park
   Acton, MA  01719
   US

   Email: quintin.zhao@huawei.com


   Kamran Raza
   Cisco Systems
   2000 Innovation Drive
   Kanata, ON K2K-3E8, MA
   Canada

   Email: E-mail: skraza@cisco.com


   Chao Zhou
   Cisco Systems
   300 Beaver Brook Road
   Boxborough, MA  01719
   US

   Email: czhou@cisco.com


   Luyuan Fang
   Microsoft

   Email: lufang@microsoft.com




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   Lianyuan Li
   China Mobile
   53A, Xibianmennei Ave.
   Xunwu District, Beijing  01719
   China

   Email: lilianyuan@chinamobile.com


   Daniel King
   Old Dog Consulting

   Email: lufang@microsoft.com






































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