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Versions: 00 01 02 03 04 draft-wijnands-mpls-mldp-multi-topology

MPLS Working Group                                    IJsbrand Wijnands
Internet Draft                                      Cisco Systems, Inc.
Intended status: Standards Track
Expires: December 19, 2013                                  Kamran Raza
                                                    Cisco Systems, Inc.


                                                          June 20, 2013


                mLDP Extensions for Multi Topology Routing

              draft-iwijnand-mpls-mldp-multi-topology-03.txt


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   carefully, as they describe your rights and restrictions with
   respect to this document.

Abstract

   The Multi-Topology Routing (MTR) enables service differentiation
   through class-based forwarding. IGP protocols (OSPF and IS-IS) have
   already been extended to setup MTR. In order to deploy mLDP in an
   MTR network, mLDP is also required to become topology-aware. This
   document specifies extensions to mLDP to support Multi-Topology
   Routing.

Table of Contents

      1. Glossary ................................................... 3
      2. Introduction ............................................... 3
      3. Conventions used in this document .......................... 4
      4. MT-Scoped mLDP FECs ........................................ 4
         4.1. MP FEC Extensions for MT .............................. 4
              4.1.1. MP FEC Element ................................. 4
              4.1.2. MT IP Address Families ......................... 5
              4.1.3. MT MP FEC Element .............................. 6
         4.2. Topology IDs .......................................... 7
     5. MT Multipoint Capability .................................... 7
     6. MT Applicability on FEC-based features ...................... 8
        6.1. Typed Wildcard MP FEC Elements ......................... 8
        6.2. End-of-LIB ............................................. 8
     7. Topology-Scoped Forwarding .................................. 9
        7.1. Upstream LSR selection ................................. 9
        7.2. Downstream forwarding interface selection .............. 9
     8. LSP Ping Extensions ......................................... 9
     9. Security Considerations .................................... 10
     10. IANA Considerations ....................................... 10
     11. References ................................................ 11
         11.1. Normative References ................................ 11
         11.2. Informative References .............................. 11
     12. Acknowledgments ........................................... 12






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1. Glossary

   MT    - Multi-Topology

   MT-ID - Multi-Topology Identifier

   MTR   - Multi-Topology Routing

   IGP   - Interior Gateway Protocol

   MP    - Multipoint (P2MP or MP2MP)

   mLDP  - Multipoint LDP

   P2MP  - Point-to-Multipoint

   MP2MP - Multipoint-to-Multipoint

   FEC   - Forwarding Equivalence Class

   LSP   - Label Switched Path

2. Introduction

   The Multi-Topology Routing (MTR) enables service differentiation
   through class-based forwarding. For example, MTR can be used to
   define separate IP topologies for voice, video, and data traffic
   classes. To support MTR, an IGP maintains independent IP topologies,
   termed as "Multi-Topologies" (MT), and computes/installs routes per
   topology. OSPF extensions [RFC4915] and ISIS extensions [RFC5120]
   specify the MT extensions under respective IGPs. To support IGP MT,
   similar LDP extensions [MT-LDP] have been proposed to make LDP MT-
   aware and be able to setup unicast Label Switched Paths (LSPs) along
   IGP MT routing paths.

   Multipoint LDP (mLDP) refers to extensions in LDP to setup multi-
   point LSPs, point-to-multipoint (P2MP) or multipoint-to-multipoint
   (MP2MP), by means of set of extensions and procedures defined in
   [RFC6388]. In order to work in an MTR network to take advantage of
   MTs, it is a natural extension to make mLDP become MT-aware. This
   document specifies the extensions to mLDP to support IGP Multi-
   Topology Routing (MTR).







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3. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

4. MT-Scoped mLDP FECs

   As defined in [MT-LDP], the Multi-Topology Identifier (MT-ID) is an
   identifier that is used to associate an LSP with a certain MTR
   topology. In the context of MP LSPs, this identifier is part of the
   mLDP FEC encoding so that LDP peers are able to setup an MP LSP via
   their own defined MTR policy. In order to avoid conflicting MTR
   policies for the same mLDP FEC, the MT-ID needs to be a part of the
   FEC, so that different MT-ID values will result in unique MP-LSP FEC
   elements.

   Since the MT-ID is part of the FEC, it will apply to all the LDP
   messages that potentially include an mLDP FEC element.

4.1. MP FEC Extensions for MT

   Following subsections propose the extensions to bind an mLDP FEC to
   a topology. The mLDP MT extensions reuse some of the extensions
   specified in [MT-LDP].

4.1.1. MP FEC Element

   Base mLDP specification [RFC6388] defines MP FEC Element 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | MP FEC type   |       Address Family          |    AF Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Root Node Address                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Opaque Length              |       Opaque Value            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: MP FEC Element Format [RFC6388]


   Where "Root Node Address" encoding is as defined for given "Address
   Family", and whose length (in octets) is specified by the "AF
   Length" field.

   To extend MP FEC elements for MT, the MT-ID is an identifier that is
   relevant in the context of the root address of the MP LSP. The MT-ID
   identifier determines in which topology the root address needs to be
   resolved. Since the MT-ID should be considered part of the mLDP FEC,
   the most natural place to encode the MT-ID is as part of the root
   address. To encode MT-ID as part of the root address, we are
   proposing to use "MT IP" Address Families as described in following
   sub section.

4.1.2. MT IP Address Families

   [MT-LDP] specification proposes new address families, named "MT IP"
   and "MT IPv6", to allow specification of an IP prefix within a
   topology scope. The Figure 2 of [MT-LDP] specification defines the
   format of the data associated with these new Address Families 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     (IP) Prefix                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |        MT-ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 2: MT IP Address Families Data Format [MT-LDP]




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   Where "(IP) Prefix" is an IPv4 or IPv6 address corresponding to "MT
   IP" and "MT IPv6" address families respectively.

4.1.3. MT MP FEC Element

   We extend MP FEC Element for MT by using MT IP Address Family (and
   its associated MT-ID) in an MP FEC Element. The resultant MT MP FEC
   element will be encoded 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | MP FEC type   |  AF (MT IP/ MT IPv6)          |    AF Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Root Node Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |        MT-ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Opaque Length              |       Opaque Value            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 3: IP MT-Scoped MP FEC Element Format


   In the context of this document, the applicable LDP FECs for MT mLDP
   include:

   o  MP FEC Elements:

       o P2MP (type 0x6)

       o MP2MP-up (type 0x7)

       o MP2MP-down (type 0x8)

   o  Typed Wildcard FEC Element (type 0x5)

   In case of "Typed Wildcard FEC Element", the sub FEC Element type
   MUST be one of the MP FECs listed above.

   This specification allows the use of Topology-scoped mLDP FECs in
   LDP label and notification messages, as applicable.





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4.2. Topology IDs

   This document assumes the same definitions and procedures associated
   with MT-ID as defined in [MT-LDP] specification.

5. MT Multipoint Capability

   "MT Multipoint Capability" is a new LDP capability, defined in
   accordance with LDP Capability definition guidelines [RFC5561], that
   is to be advertised to its peers by an mLDP speaker to announce its
   capability to support MTR and the procedures specified in this
   document. This capability MAY be sent either in an Initialization
   message at the session establishment time, or in a Capability
   message dynamically during the lifetime of a session (only if
   "Dynamic Announcement" capability [RFC5561] has been successfully
   negotiated with the peer).

   The format of this capability 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F|  MT Multipoint Cap.(IANA) |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S| Reserved    |
   +-+-+-+-+-+-+-+-+

              Figure 4: "MT Multipoint Capability" TLV Format


   Where:

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

     MT Multipoint Capaility: TLV type (IANA assigned).

     Length: The length (in octets) of TLV. The value of this field
        MUST be 1 as there is no Capability-specific data [RFC5561]
        that follows in the TLV.

     S-bit: Set to 1 to announce and 0 to withdraw the capability (as
        per [RFC5561]).

   An mLDP speaker that has successfully advertised and negotiated "MT
   Multipoint" capability MUST support the following:



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  1. Topology-scoped mLDP FECs in LDP messages ( Section 4.1. )

  2. Topology-scoped mLDP forwarding setup ( Section 7. )

6. MT Applicability on FEC-based features

6.1. Typed Wildcard MP FEC Elements

   [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 for a given type of FEC.

   The MT extensions proposed in document do not require any extension
   in procedures for Typed Wildcard FEC Element support [RFC5918], and
   these procedures apply as-is to Multipoint MT FEC wildcarding. Like
   Typed Wildcard MT Prefix FEC Element, as defined in [MT-LDP], the MT
   extensions allow use of "MT IP" or "MT IPv6" in the Address Family
   field of the Typed Wildcard MP FEC element in order to use wildcard
   operations for MP FECs in the context of a given topology as
   identified by the MT-ID field.

   This document proposes following format and encoding for a Typed
   Wildcard MP FEC element:

    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)| Type = MP FEC |   Len = 6     |  AF = MT IP ..|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |... or MT IPv6 |         Reserved              |    MT ID      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |MT ID (contd.) |
   +-+-+-+-+-+-+-+-+

               Figure 5: "Typed Wildcard MT MP FEC Element"

   Where:

   Type: One of MP FEC Element type (P2MP, MP2MPup, MP2MP-down).

   The proposed format allows an LSR to perform wildcard MP FEC
   operations under the scope of a topology.

6.2. End-of-LIB

   [RFC5919] specifies extensions and procedures that allows an LDP
   speaker to signal its End-of-LIB (i.e. convergence) for a given FEC


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   type towards a peer. MT extensions for MP FEC do not require any
   change in these procedures and they apply as-is to MT MP FEC
   elements. This means that an MT mLDP speaker MAY signal its
   convergence per topology using MT Typed Wildcard MP FEC element.

7. Topology-Scoped Forwarding

   Since the MT-ID is part of an mLDP FEC, there is no need to support
   the concept of multiple topology tables in mLDP. Each MP LSP will be
   unique due to the MT-ID being part of the FEC. There is also no need
   to have specific label forwarding tables per topology, and each MP
   LSP will have its own unique local label in the table. However, In
   order to implement MTR in an mLDP network, the selection procedures
   for upstream LSR and downstream forwarding interface need be
   changed.

7.1. Upstream LSR selection

   The procedures as described in RFC-6388 section-2.4.1.1 depend on
   the best path to reach the root. When the MT-ID is signaled as part
   of the FEC, the MT-ID is used to select the topology that must be
   used to find the best path to the root address. Using the next-hop
   from this best path, a LDP peer is selected following the procedures
   as defined in [RFC6388].

7.2. Downstream forwarding interface selection

   The procedures as described in RFC-6388 section-2.4.1.2 describe how
   a downstream forwarding interface is selected. In these procedures,
   any interface leading to the downstream LDP neighbor can be
   considered as candidate forwarding interface. When the MT-ID is part
   of the FEC, this is no longer true. An interface must only be
   selected if it is part of the same topology that was signaled in the
   mLDP FEC element. Besides this restriction, the other procedures in
   [RFC6388] apply.

8. LSP Ping Extensions

   [RFC6425] defines procedures to detect data plane failures in
   Multipoint MPLS LSPs. Section 3.1.2 of [RFC6425] defines new Sub-
   Types and Sub-TLVs for Multipoint LDP FECs to be sent in "Target FEC
   Stack" TLV of an MPLS echo request message [RFC4379].

   To support LSP ping for MT Multipoint LSPs, this document uses
   existing sub-types "P2MP LDP FEC Stack" and "MP2MP LDP FEC Stack"
   defined in [RFC6425]. The proposed extension is to specify "MT IP"
   or "MT IPv6" in the "Address Family" field, set the "Address Length"


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   field to 8 (for MT IP) or 20 (for MT IPv6), and encode the sub-TLV
   with additional MT-ID information as an extension to the "Root LSR
   Address" field. The resultant format of sub-tlv 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Address Family (MT IP/MT IPv6) | Address Length|               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
   ~                   Root LSR Address (Cont.)                    ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |        MT-ID                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Opaque Length          |         Opaque Value ...      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   ~                                                               ~
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 6: Multipoint LDP FEC Stack Sub-TLV Format for MT

   The rules and procedures of using this new sub-TLV in an MPLS echo
   request message are same as defined for P2MP/MP2MP LDP FEC Stack
   Sub-TLV in [RFC6425] with only difference being that Root LSR
   address is now topology scoped.

9. Security Considerations

   This extension to mLDP does not introduce any new security
   considerations beyond that already apply to the base LDP
   specification [RFC5036], base mLDP specification [RFC6388], and MPLS
   security framework [RFC5920].

10. IANA Considerations

   This document defines a new LDP capability parameter TLV. IANA is
   requested to assign the lowest available value after 0x0500 from
   "TLV Type Name Space" in the "Label Distribution Protocol (LDP)
   Parameters" registry within "Label Distribution Protocol (LDP) Name
   Spaces" as the new code point for the LDP TLV code point.





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   +-----+------------------+---------------+-------------------------+
   |Value| Description      | Reference     | Notes/Registration Date |
   +-----+------------------+---------------+-------------------------+
   | TBA | MT Multipoint    | This document |                         |
   |     | Capability       |               |                         |
   +-----+------------------+---------------+-------------------------+


11. References

11.1. Normative References

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

   [RFC4915] P. Psenak, S. Mirtorabi, A. Roy, L. Nguyen, P. Pillay-
             Esnault, "Multi-Topology Routing in OSPF", RFC 4915, June
             2007.

   [RFC5120] T. Przygienda, Z2 Sagl, N. Shen, N. Sheth, "M-ISIS: Multi-
             Topology Routing in IS-IS", RFC 5120, February 2008.

   [MT-LDP]  Q. Zhao, L. Fang, C. Zhou, L. Li, K. Raza, "LDP Extensions
             for Multiple Topology Routing", draft-ietf-mpls-ldp-multi-
             topology-08, Work in progress, May 2013.

   [RFC6388] I. Minei, I. Wijnands, K. Kompella, B. Thomas,
             "LDP Extensions for P2MP and MP2MP LSPs", RFC 6388,
             November 2011.

   [RFC4379] S. Sexana, G. Swallow, Z. Ali, A. Farrel, S. Yasukawa,
             T. Nadeau, "Detecting Multi-Protocol Label Switched (MPLS)
             Data Plane Failures", RFC 4379, February 2006.

   [RFC6425] Kompella, K. and G. Swallow, "Detecting Data-Plane Failures
             in Point-to-Multipoint MPLS - Extensions to LSP Ping",
             RFC 6425, November 2011.


11.2. Informative References

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

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

   [RFC5918] R. Asati, I. Minei, B. Thomas, "Label Distribution
             Protocol Typed Wildcard FEC", RFC 5918, August 2010.



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

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

12. Acknowledgments

   The authors would like to acknowledge Eric Rosen for his input on
   this specification.

   This document was prepared using 2-Word-v2.0.template.dot.



Authors' Addresses

   IJsbrand Wijnands
   Cisco Systems, Inc.
   De kleetlaan 6a,
   Diegem  1831 Belgium.
   Email: ice@cisco.com


   Kamran Raza
   Cisco Systems, Inc.
   2000 Innovation Drive,
   Kanata, Ontario K2K-3E8, Canada.
   Email: skraza@cisco.com













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