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Versions: (draft-beckhaus-ldp-dod) 00 01 02 RFC 7032

Network Working Group                                        T. Beckhaus
Internet-Draft                                       Deutsche Telekom AG
Intended status: Informational                               B. Decraene
Expires: July 7, 2012                                     France Telecom
                                                         K. Tiruveedhula
                                                      M. Konstantynowicz
                                                        Juniper Networks
                                                              L. Martini
                                                     Cisco Systems, Inc.
                                                        January 04, 2012


               LDP Downstream-on-Demand in Seamless MPLS
                       draft-ietf-mpls-ldp-dod-00

Abstract

   Seamless MPLS design enables a single IP/MPLS network to scale over
   core, metro and access parts of a large packet network infrastructure
   using standardized IP/MPLS protocols.  One of the key goals of
   Seamless MPLS is to meet requirements specific to access, including
   high number of devices, their position in network topology and their
   compute and memory constraints that limit the amount of state access
   devices can hold.This can be achieved with LDP Downstream-on-Demand
   (LDP DoD) label advertisement.  This document describes LDP DoD use
   cases and lists required LDP DoD procedures in the context of
   Seamless MPLS design.

   In addition, a new optional TLV type in the LDP label request message
   is defined for fast-up convergence.

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 RFC2119 [RFC2119].

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



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   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 July 7, 2012.

Copyright Notice

   Copyright (c) 2012 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.































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Reference Topologies . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Access Topologies with Static Routing  . . . . . . . . . .  6
     2.2.  Access Topologies with Access IGP  . . . . . . . . . . . .  9
   3.  LDP DoD Use Cases  . . . . . . . . . . . . . . . . . . . . . . 11
     3.1.  Initial Network Setup  . . . . . . . . . . . . . . . . . . 11
       3.1.1.  AN with Static Routing . . . . . . . . . . . . . . . . 11
       3.1.2.  AN with Access IGP . . . . . . . . . . . . . . . . . . 13
     3.2.  Service Provisioning and Activation  . . . . . . . . . . . 13
     3.3.  Service Changes and Decommissioning  . . . . . . . . . . . 16
     3.4.  Service Failure  . . . . . . . . . . . . . . . . . . . . . 16
     3.5.  Network Transport Failure  . . . . . . . . . . . . . . . . 17
       3.5.1.  General Notes  . . . . . . . . . . . . . . . . . . . . 17
       3.5.2.  AN Node Failure  . . . . . . . . . . . . . . . . . . . 17
       3.5.3.  AN/AGN Link Failure  . . . . . . . . . . . . . . . . . 18
       3.5.4.  AGN Node Failure . . . . . . . . . . . . . . . . . . . 19
       3.5.5.  AGN Network-side Reachability Failure  . . . . . . . . 19
   4.  LDP DoD Procedures . . . . . . . . . . . . . . . . . . . . . . 20
     4.1.  LDP Label Distribution Control and Retention Modes . . . . 20
     4.2.  IPv6 Support . . . . . . . . . . . . . . . . . . . . . . . 21
     4.3.  LDP DoD Session Negotiation  . . . . . . . . . . . . . . . 22
     4.4.  Label Request Procedures . . . . . . . . . . . . . . . . . 22
       4.4.1.  Access LSR/ABR Label Request . . . . . . . . . . . . . 22
       4.4.2.  Label Request Retry  . . . . . . . . . . . . . . . . . 23
       4.4.3.  Label Request with Fast-Up Convergence . . . . . . . . 24
     4.5.  Label Withdraw . . . . . . . . . . . . . . . . . . . . . . 26
     4.6.  Label Release  . . . . . . . . . . . . . . . . . . . . . . 27
     4.7.  Local Repair . . . . . . . . . . . . . . . . . . . . . . . 27
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 27
     5.1.  LDP TLV TYPE . . . . . . . . . . . . . . . . . . . . . . . 28
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 28
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 28
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29













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1.  Introduction

   Seamless MPLS design [I-D.ietf-mpls-seamless-mpls] enables a single
   IP/MPLS network to scale over core, metro and access parts of a large
   packet network infrastructure using standardized IP/MPLS protocols.
   One of the key goals of Seamless MPLS is to meet requirements
   specific to access, including high number of devices, their position
   in network topology and their compute and memory constraints that
   limit the amount of state access devices can hold.

   In general MPLS routers implement either LDP or RSVP for MPLS label
   distribution.  The focus of this document is on LDP, as Seamless MPLS
   design does not include a requirement for general purpose explicit
   traffic engineering and bandwidth reservation.  This document is
   focusing on the unicast connectivity only.  Multicast connectivity is
   subject for further study.

   In Seamless MPLS design [I-D.ietf-mpls-seamless-mpls], IP/MPLS
   protocol optimization is possible due to a relatively simple access
   network topologies.  Examples of such topologies involving access
   nodes (AN) and aggregation nodes (AGN) include:

   a.  A single AN homed to a single AGN.

   b.  A single AN dual-homed to two AGNs.

   c.  Multiple ANs daisy-chained via a hub-AN to a single AGN.

   d.  Multiple ANs daisy-chained via a hub-AN to two AGNs.

   e.  Two ANs dual-homed to two AGNs.

   f.  Multiple ANs chained in a ring and dual-homed to two AGNs.

   The amount of IP RIB and FIB state on ANs can be easily controlled in
   the listed access topologies by using simple IP routing configuration
   with either static routes or dedicated access IGP.  Note that in all
   of the above topologies AGNs act as the access border routers (access
   ABRs) connecting the access topology to the rest of the network.
   Hence in many cases it is sufficient for ANs to have a default route
   pointing towards AGNs in order to achieve complete network
   connectivity from ANs to the network.

   The amount of MPLS forwarding state however requires additional
   consideration.  In general MPLS routers implement LDP Downstream
   Unsolicited (LDP DU) label advertisement [RFC5036] and advertise MPLS
   labels for all valid routes in their RIB.  This is seen as a very
   insufficient approach for ANs, as they only require a small subset of



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   the total routes (and associated labels) based on the required
   connectivity for the provisioned services.  And although filters can
   be applied to those LDP DU labels advertisements, it is not seen as a
   suitable tool to facilitate any-to-any AN-driven connectivity between
   access and the rest of the MPLS network.

   This document describes an access node driven "subscription model"
   for label distribution in the access.  The approach relies on the
   standard LDP Downstream-on-Demand (LDP DoD) label advertisements as
   specified in [RFC5036].  LDP DoD enables on-demand label distribution
   ensuring that only required labels are requested, provided and
   installed.

   Note that LDP DoD implementation is not widely available in today's
   IP/MPLS devices despite the fact that it has been described in the
   LDP specification [RFC5036].  This is due to the fact that the
   originally LDP DoD advertisement mode was aimed mainly at ATM and
   Frame Relay MPLS implementations, where conserving label space used
   on the links was essential for compatibility with ATM and Frame Relay
   LSRs.

   The following sections describe a set of reference access topologies
   considered for LDP DoD usage and their associated IP routing
   configurations, followed by LDP DoD use cases and LDP DoD procedures
   in the context of Seamless MPLS design.


2.  Reference Topologies

   LDP DoD use cases are described in the context of a generic reference
   end-to-end network topology based on Seamless MPLS design
   [I-D.ietf-mpls-seamless-mpls] shown in Figure 1



















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                  +-------+  +-------+  +------+  +------+
               ---+ AGN11 +--+ AGN21 +--+ ABR1 +--+ LSR1 +--> to LSR/AGN
    +--------+/   +-------+  +-------+  +------+  +------+
    | Access |             \/                   \/
    | Network|             /\                   /\
    +--------+    +-------+  +-------+  +------+  +------+
              \---+ AGN12 +--+ AGN22 +--+ ABR2 +--+ LSR2 +--> to LSR/AGN
                  +-------+  +-------+  +------+  +------+

       static routes
       or access IGP        ISIS L1               ISIS L2
      <----Access----><--Aggregation Domain--><----Core----->
      <------------------------- MPLS ---------------------->

      Figure 1: Seamless MPLS end-to-end reference network topology.

   The access network is either single or dual homed to AGN1x, with
   either a single or multiple parallel links to AGN1x.

   Seamless MPLS access network topologies can range from a single- or
   dual-homed access node to a chain or ring of access nodes, and use
   either static routing or access IGP.  The following sections describe
   reference access topologies in more detail.

2.1.  Access Topologies with Static Routing

   In most cases access nodes connect to the rest of the network using
   very simple topologies.  Here static routing is sufficient to provide
   the required IP connectivity.  The following topologies are
   considered for use with static routing and LDP DoD:

   a.  [I1] topology - a single AN homed to a single AGN.

   b.  [I] topology - multiple ANs daisy-chained to a single AGN.

   c.  [V] topology - a single AN dual-homed to two AGNs.

   d.  [U2] topology - two ANs dual-homed to two AGNs.

   e.  [Y] topology - multiple ANs daisy-chained to two AGNs.

   The reference static routing and LDP configuration for [V] access
   topology is shown in Figure 2.  The same static routing and LDP
   configuration also applies to [I1] topology.







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         +----+                        +-------+
         |AN1 +------------------------+ AGN11 +-------
         |    +-------\    /-----------+       +-\    /
         +----+        \  /            +-------+  \  /
                        \/                         \/
                        /\                         /\
         +----+        /  \            +-------+  /  \
         |AN2 +-------/    \-----------+ AGN12 +-/    \
         |    +------------------------+       +-------
         +----+                        +-------+

         --(u)->                        <-(d)--

            <----- static routing -------> <--- ISIS --->
                                           <-- LDP DU -->
            <--------- LDP DoD ----------> <-- BGP LU -->

     (u) static routes: 0/0 default, (optional) /32 or /128 destinations
     (d) static routes: /32 or /128 AN loopbacks

             Figure 2: [V] access topology with static routes.

   In line with the Seamless MPLS design, static routes configured on
   AGN1x and pointing towards the access network are redistributed in
   either ISIS or BGP labeled unicast (BGP-LU) [RFC3107].

   The reference static routing and LDP configuration for [U2] access
   topology is shown in Figure 3.























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                +----+                        +-------+
          (d1)  |AN1 +------------------------+ AGN11 +-------
           |    |    +                        +       +-\    /
           v    +-+--+                        +-------+  \  /
                  |                                       \/
                  |                                       /\
           ^    +-+--+                        +-------+  /  \
           |    |AN2 +                        + AGN12 +-/    \
          (d2)  |    +------------------------+       +-------
                +----+                        +-------+

                --(u)->                        <-(d)--

                <------- static routing --------> <--- ISIS --->
                                                  <-- LDP DU -->
                <----------- LDP DoD -----------> <-- BGP LU -->

    (u) static route 0/0 default (/32 or /128 destinations optional)
    (d) static route for /32 or /128 AN loopbacks
    (d1) static route for /32 or /128 AN2 loopback and 0/0 default with lower preference
    (d2) static route for /32 or /128 AN1 loopback and 0/0 default with lower preference

            Figure 3: [U2] access topology with static routes.

   The reference static routing and LDP configuration for [Y] access
   topology is shown in Figure 4.  The same static routing and LDP
   configuration also applies to [I] topology.
























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                                         +-------+
                                         |       |---/
                                    /----+ AGN11 |
      +----+   +----+   +----+     /     |       |---\
      |    |   |    |   |    +----/      +-------+
      |ANn +...|AN2 +---+AN1 |
      |    |   |    |   |    +----\      +-------+
      +----+   +----+   +----+     \     |       |---/
                                    \----+ AGN12 |
             <-(d2)--  <-(d1)--          |       |---\
      --(u)-> --(u)->   --(u)->          +-------+
                                         <-(d)--

            <------- static routing -------> <--- ISIS --->
                                             <-- LDP DU -->
            <---------- LDP DoD -----------> <-- BGP LU -->

     (u) static routes: 0/0 default, (optional) /32 or /128 destinations
     (d) static routes: /32 or /128 AN loopbacks [1..n]
     (d1) static routes: /32 or /128 AN loopbacks [2..n]
     (d2) static routes: /32 or /128 AN loopbacks [3..n]

             Figure 4: [Y] access topology with static routes.

   Note that in all of the above topologies parallel ECMP (or L2 LAG)
   links can be used between the nodes.

   ANs support Inter-area LDP [RFC5283] in order to use the IP default
   route to match the LDP FEC advertised by AGN1x and other ANs.

2.2.  Access Topologies with Access IGP

   A dedicated access IGP instance is used in the access network to
   perform the internal routing between AGN1x and connected AN devices.
   Example of such IGP could be ISIS, OSPFv2&v3, RIPv2&RIPng.  This
   access IGP instance is distinct from the IGP of the aggegation
   domain.

   The following topologies are considered for use with access IGP
   routing and LDP DoD:

   a.  [U] topology - multiple ANs chained in an open ring and dual-
       homed to two AGNs.

   b.  [Y] topology - multiple ANs daisy-chained via a hub-AN to two
       AGNs.

   The reference access IGP and LDP configuration for [U] access



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   topology is shown in Figure 5.

                                            +-------+
             +-----+   +-----+   +----+     |       +---/
             | AN3 |---| AN2 |---|AN1 +-----+ AGN11 |
             +-----+   +-----+   +----+     |       +---\
                .                           +-------+
                .
                .                           +-------+
             +-----+   +-----+   +----+     |       +---/
             |ANn-2|---|ANn-1|---|ANn +-----+ AGN12 |
             +-----+   +-----+   +----+     |       +---\
                                            +-------+

             <---------- access IGP ------------> <--- ISIS --->
                                                  <-- LDP DU -->
             <------------ LDP DoD -------------> <-- BGP LU -->

              Figure 5: [U] access topology with access IGP.

   The reference access IGP and LDP configuration for [Y] access
   topology is shown in Figure 6.

                                               +-------+
                                               |       |---/
                                          /----+ AGN11 |2
            +----+   +----+   +----+     /     |       |---\
            |    |   |    |   |    +----/      +-------+
            |ANn +...|AN2 +---+AN1 |
            |    |   |    |   |    +----\      +-------+
            +----+   +----+   +----+     \     |       |---/
                                          \----+ AGN12 |
                                               |       |---\
                                               +-------+

             <---------- access IGP ------------> <--- ISIS --->
                                                  <-- LDP DU -->
             <------------ LDP DoD -------------> <-- BGP LU -->

              Figure 6: [Y] access topology with access IGP.

   Note that in all of the above topologies parallel ECMP (or L2 LAG)
   links can be used between the nodes.

   In both of the above topologies, ANs (ANn ...  AN1) and AGN1x share
   the access IGP and advertise their IPv4 and IPv6 loopbacks and link
   addresses.  AGN1x advertise a default route into the access IGP.




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   ANs support Inter-area LDP [RFC5283] in order to use the IP default
   route for matching the LDP FECs advertised by AGN1x or other ANs.


3.  LDP DoD Use Cases

   LDP DoD operation is driven by Seamless MPLS use cases.  This section
   illustrates these use cases focusing on services provisioned on the
   access nodes and clarifies expected LDP DoD operation on the AN and
   AGN1x devices.  Two representative service types are used to
   illustrate the service use cases: MPLS PWE3 [RFC4447] and BGP/MPLS
   IPVPN [RFC4364].

   Described LDP DoD operations apply equally to all reference access
   topologies described in Section 2.  Operations that are specific to
   certain access topologies are called out explicitly.

   References to upstream and downstream nodes are made in line with the
   definition of upstream and downstream LSR [RFC3031].

   This document is focusing on IPv4 LDP DoD procedures.  Similar
   procedures are required for IPv6 LDP DoD, however some extension
   specific to IPv6 are likely to apply including LSP mapping, peer
   discovery, transport connection establishment.  These will be added
   in this document once LDP IPv6 standardization is advanced as per
   [I-D.ietf-mpls-ldp-ipv6].

3.1.  Initial Network Setup

   An access node is commissioned without any services provisioned on
   it.  The AN may request labels for loopback addresses of any AN, AGN
   or other nodes within Seamless MPLS network for operational and
   management purposes.  It is assumed that AGN1x has required IP/MPLS
   configuration for network-side connectivity in line with Seamless
   MPLS design [I-D.ietf-mpls-seamless-mpls].

   LDP sessions are configured between adjacent ANs and AGN1x using
   their respective loopback addresses.

3.1.1.  AN with Static Routing

   If access static routing is used, ANs are provisioned with the
   following static IP routing entries (topology references from
   Section 2 are listed in square brackets):

   a.  [I1, V, U2] - Static default route 0/0 pointing to links
       connected to AGN1x.  Requires support for Inter-area LDP
       [RFC5283].



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   b.  [U2] - Static /32 or /128 routes pointing to the other AN.  Lower
       preference static default route 0/0 pointing to links connected
       to the other AN.  Requires support for Inter-area LDP [RFC5283].

   c.  [I, Y] - Static default route 0/0 pointing to links leading
       towards AGN1x.  Requires support for Inter-area LDP [RFC5283].

   d.  [I, Y] - Static /32 or /128 routes to all ANs in the daisy-chain
       pointing to links towards those ANs.

   e.  [I1, V, U2] - Optional - Static /32 or /128 routes for specific
       nodes within Seamless MPLS network, pointing to links connected
       to AGN1x.

   f.  [I, Y] - Optional - Static /32 or /128 routes for specific nodes
       within the Seamless MPLS network, pointing to links leading
       towards AGN1x.

   Upstream AN/AGN1x should request labels over LDP DoD session(s) from
   downstream AN/AGN1x for configured static routes if those static
   routes are configured with LDP DoD request policy and if they are
   pointing to a next-hop selected by routing.  It is expected that all
   configured /32 and /128 static routes to be used for LDP DoD are
   configured with such policy on AN/AGN1x.

   Downstream AN/AGN1x should respond to the label request from the
   upstream AN/AGN1x with a label mapping (if requested route is present
   in its RIB, and there is a valid label binding from its downstream),
   and must install the advertised label as an incoming label in its
   label table (LIB) and its forwarding table (LFIB).  Upstream AN/AGN1x
   must also install the received label as an outgoing label in their
   LIB and LFIB.  If the downstream AN/AGN1x does have the route present
   in its RIB, but does not have a valid label binding from its
   downstream, it should forward the request to its downstream.

   In order to facilitate ECMP and IPFRR LFA local-repair, the upstream
   AN/AGN1x must also send LDP DoD label requests to alternate next-hops
   per its RIB, and install received labels as alternate entries in its
   LIB and LFIB.

   AGN1x node on the network side may use BGP labeled unicast [RFC3107]
   in line with the Seamless MPLS design [I-D.ietf-mpls-seamless-mpls].
   In such a case AGN1x will be redistributing its static routes
   pointing to local ANs into BGP labeled unicast to facilitate network-
   to-access traffic flows.  Likewise, to facilitate access-to-network
   traffic flows, AGN1x will be responding to access-originated LDP DoD
   label requests with label mappings based on its BGP labeled unicast
   reachability for requested FECs.



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3.1.2.  AN with Access IGP

   If access IGP is used, AN(s) advertise their loopbacks over the
   access IGP with configured metrics.  AGN1x advertise a default route
   over the access IGP.

   Similarly to the static route case, upstream AN/AGN1x should request
   labels over LDP DoD session(s) from downstream AN/AGN1x for all /32
   or /128 routes received over the access IGP.

   Identically to the static route case, downstream AN/AGN1x should
   respond to the label request from the upstream AN/AGN1x with a label
   mapping (if the requested route is present in its RIB, and there is a
   valid label binding from its downstream), and must install the
   advertised label as an incoming label in its LIB and LFIB.  Upstream
   AN/AGN1x must also install the received label as an outgoing label in
   their LIB and LFIB.

   Identically to the static route case, in order to facilitate ECMP and
   IPFRR LFA local-repair, upstream AN/AGN1x must also send LDP DoD
   label requests to alternate next-hops per its RIB, and install
   received labels as alternate entries in its LIB and LFIB.

   AGN1x node on the network side may use BGP labeled unicast [RFC3107]
   in line with Seamless MPLS design [I-D.ietf-mpls-seamless-mpls].  In
   such case AGN1x will be redistributing routes received over the
   access IGP (and pointing to local ANs), into BGP labeled unicast to
   facilitate network-to-access traffic flows.  Likewise, to facilitate
   access-to-network traffic flows AGN1x will be responding to access
   originated LDP DoD label requests with label mappings based on its
   BGP labeled unicast reachability for requested FECs.

3.2.  Service Provisioning and Activation

   Following the initial setup phase described in Section 3.1, a
   specific access node, referred to as AN*, is provisioned with a
   network service.  AN* relies on LDP DoD to request the required MPLS
   LSP(s) label(s) from downstream AN/AGN1x node(s).  Note that LDP DoD
   operations are service agnostic, that is, they are the same
   independently of the services provisioned on the AN*.

   For illustration purposes two service types are described: MPLS PWE3
   [RFC4447] service and BGP/MPLS IPVPN [RFC4364].

   MPLS PWE3 service - for description simplicity it is assumed that a
   single segment pseudowire is signaled using targeted LDP FEC128
   (0x80), and it is provisioned with the pseudowire ID and the loopback
   IPv4 address of the destination node.  The following IP/MPLS



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   operations need to be completed on the AN* to successfully establish
   such PWE3 service:

   a.  LSP labels for destination /32 FEC (outgoing label) and the local
       /32 loopback (incoming label) need to be signaled using LDP DoD.

   b.  Targeted LDP session over an associated TCP/IP connection needs
       to be established to the PWE3 destination PE.  This is triggered
       by either an explicit targeted LDP session configuration on the
       AN* or automatically at the time of provisioning the PWE3
       instance.

   c.  Local and remote PWE3 labels for specific FEC128 PW ID need to be
       signaled using targeted LDP and PWE3 signaling procedures
       [RFC4447].

   d.  Upon successful completion of the above operations, AN* programs
       its RIB/LIB and LFIB tables, and activates the MPLS PWE3 service.

   Note - only minimum operations applicable to service connectivity
   have been listed.  Other non IP/MPLS connectivity operations that may
   be required for successful service provisioning and activation are
   out of scope in this document.

   BGP/MPLS IPVPN service - for description simplicity it is assumed
   that AN* is provisioned with a unicast IPv4 IPVPN service (VPNv4 for
   short) [RFC4364].  The following IP/MPLS operations need to be
   completed on the AN* to successfully establish VPNv4 service:

   a.  BGP peering sessions with associated TCP/IP connections need to
       be established with the remote destination VPNv4 PEs or Route
       Reflectors.

   b.  Based on configured BGP policies, VPNv4 BGP NLRIs need to be
       exchanged between AN* and its BGP peers.

   c.  Based on configured BGP policies, VPNv4 routes need to be
       installed in the AN* VRF RIB and FIB, with corresponding BGP
       next-hops.

   d.  LSP labels for destination BGP next-hop /32 FEC (outgoing label)
       and the local /32 loopback (incoming label) need to be signaled
       using LDP DoD.

   e.  Upon successful completion of above operations, AN* programs its
       RIB/LIB and LFIB tables, and activates the BGP/MPLS IPVPN
       service.




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   Note - only minimum operations applicable to service connectivity
   have been listed.  Other non IP/MPLS connectivity operations that may
   be required for successful service provisioning are out of scope in
   this document.

   To establish an LSP for destination /32 FEC for any of the above
   services, AN* looks up its local routing table for a matching route,
   selects the best next-hop(s) and associated outgoing link(s).

   If a label for this /32 FEC is not already installed based on the
   configured static route with LDP DoD request policy or access IGP RIB
   entry, AN* must send an LDP DoD label mapping request.  Downstream
   AN/AGN1x LSR(s) checks its RIB for presence of the requested /32 and
   associated valid outgoing label binding, and if both are present,
   replies with its label for this FEC and installs this label as
   incoming in its LIB and LFIB.  Upon receiving the label mapping the
   AN* must accept this label based on the exact route match of
   advertised FEC and route entry in its RIB or based on the longest
   match in line with Inter-area LDP [RFC5283].  If the AN* accepts the
   label it must install it as an outgoing label in its LIB and LFIB.

   In access topologies [V] and [Y], if AN* is dual homed to two AGN1x
   and routing entries for these AGN1x are configured as equal cost
   paths, AN* must send LDP DoD label requests to both AGN1x devices and
   install all received labels in its LIB and LFIB.

   In order for AN* to implement IPFRR LFA local-repair, AN* must also
   send LDP DoD label requests to alternate next-hops per its RIB, and
   install received labels as alternate entries in its LIB and LFIB.

   When forwarding PWE3 or VPNv4 packets AN* chooses the LSP label based
   on the locally configured static /32 or default route, or default
   route signaled via access IGP.  If a route is reachable via multiple
   interfaces to AGN1x nodes and the route has multiple equal cost
   paths, AN* must implement Equal Cost Multi-Path (ECMP) functionality.
   This involves AN* using hash-based load-balancing mechanism and
   sending the PWE3 or VPNv4 packets in a flow-aware manner with
   appropriate LSP labels via all equal cost links.

   ECMP mechanism is applicable in an equal manner to parallel links
   between two network elements and multiple paths towards the
   destination.  The traffic demand is distributed over the available
   paths.

   AGN1x node on the network side may use BGP labeled unicast [RFC3107]
   in line with Seamless MPLS design [I-D.ietf-mpls-seamless-mpls].  In
   such case AGN1x will be redistributing its static routes (or routes
   received from the access IGP) pointing to local ANs into BGP labeled



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   unicast to facilitate network-to-access traffic flows.  Likewise, to
   facilitate access-to-network traffic flows AGN1x will be responding
   to access originated LDP DoD label requests with label mappings based
   on its BGP labeled unicast reachability for requested FECs.

3.3.  Service Changes and Decommissioning

   Whenever AN* service gets decommissioned or changed and connectivity
   to specific destination is not longer required, the associated MPLS
   LSP label resources should be released on AN*.

   MPLS PWE3 service - if the PWE3 service gets decommissioned and it is
   the last PWE3 to a specific destination node, the targeted LDP
   session is not longer needed and should be terminated (automatically
   or by configuration).  The MPLS LSP(s) to that destination is no
   longer needed either.

   BGP/MPLS IPVPN service - deletion of a specific VPNv4 (VRF) instance,
   local or remote re-configuration may result in specific BGP next-
   hop(s) being no longer needed.  The MPLS LSP(s) to that destination
   is no longer needed either.

   In all of the above cases the following LDP DoD related operations
   apply:

   o  If the /32 FEC label for the aforementioned destination node was
      originally requested based on either tLDP session configuration
      and default route or required BGP next-hop and default route, AN*
      should delete the label from its LIB and LFIB, and release it from
      downstream AN/AGN1x by using LDP DoD procedures.

   o  If the /32 FEC label was originally requested based on the static
      /32 route configuration with LDP DoD request policy, the label
      must be retained by AN*.

3.4.  Service Failure

   A service instance may stop being operational due to a local or
   remote service failure event.

   In general, unless the service failure event modifies required MPLS
   connectivity, there should be no impact on the LDP DoD operation.

   If the service failure event does modify the required MPLS
   connectivity, LDP DoD operations apply as described in Section 3.2
   and Section 3.3.





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3.5.  Network Transport Failure

   A number of different network events can impact services on AN*.  The
   following sections describe network event types that impact LDP DoD
   operation on AN and AGN1x nodes.

3.5.1.  General Notes

   If service on any of the ANs is affected by any network failure and
   there is no network redundancy, the service must go into a failure
   state.  When the network failure is recovered from, the service must
   be re-established automatically.

   The following additional LDP-related functions should be supported to
   comply with Seamless MPLS [I-D.ietf-mpls-seamless-mpls] fast service
   restoration requirements as follows:

   a.  Local-repair - AN and AGN1x should support local-repair for
       adjacent link or node failure for access-to-network, network-to-
       access and access-to-access traffic flows.  Local-repair should
       be implemented by using either IPFRR LDP LFA, simple ECMP or
       primary/backup switchover upon failure detection.

   b.  LDP session protection - LDP sessions should be configured with
       LDP session protection to avoid delay upon the recovery from link
       failure.  LDP session protection ensures that FEC label binding
       is maintained in the control plane as long as LDP session stays
       up.

   c.  IGP-LDP synchronization - If access IGP is used, LDP sessions
       between ANs, and between ANs and AGN1x, should be configured with
       IGP-LDP synchronization to avoid unnecessary traffic loss in case
       the access IGP converged before LDP and there is no LDP label
       binding to the downstream best next-hop.

3.5.2.  AN Node Failure

   AN node fails and all links to adjacent nodes go down.

   Adjacent AN/AGN1x nodes remove all routes pointing to the failed
   link(s) from their RIB tables (including /32 loopback belonging to
   the failed AN and any other routes reachable via the failed AN).
   This in turn triggers the removal of associated outgoing /32 FEC
   labels from their LIB and LFIB tables.

   If access IGP is used, the AN node failure will be propagated via IGP
   link updates across the access topology.




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   If a specific /32 FEC(s) is not reachable anymore from those AN/
   AGN1x, they must also send LDP label withdraw to their upstream LSRs
   to notify about the failure, and remove the associated incoming
   label(s) from their LIB and LFIB tables.  Upstream LSRs upon
   receiving label withdraw should remove the signaled labels from their
   LIB/LFIB tables, and propagate LDP label withdraw across their
   upstream LDP DoD sessions.

   In [U] topology there may be an alternative path to routes previously
   reachable via the failed AN node.  In this case adjacent AN/AGN1x
   should invoke local-repair (IPFRR LFA, ECMP) and switchover to
   alternate next-hop to reach those routes.

   AGN1x gets notified about the AN failure via either access IGP (if
   used) and/or cascaded LDP DoD label withdraw(s).  AGN1x must
   implement all relevant global-repair IP/MPLS procedures to propagate
   the AN failure towards the core network.  This should involve
   removing associated routes (in access IGP case) and labels from its
   LIB and LFIB tables, and propagating the failure on the network side
   using BGP-LU and/or core IGP/LDP-DU procedures.

   Upon AN coming back up, adjacent AN/AGN1x nodes automatically add
   routes pointing to recovered links based on the configured static
   routes or access IGP adjacency and link state updates.  This should
   be then followed by LDP DoD label signaling and subsequent binding
   and installation of labels in LIB and LFIB tables.

3.5.3.  AN/AGN Link Failure

   Depending on the access topology and the failed link location
   different cases apply to the network operation after AN link failure
   (topology references from Section 2 in square brackets):

   a.  [all] - link failed, but at least one ECMP parallel link remains
       - nodes on both sides of the failed link must stop using the
       failed link immediately (local-repair), and keep using the
       remaining ECMP parallel links.

   b.  [I1, I, Y] - link failed, and there are no ECMP or alternative
       links and paths - nodes on both sides of the failed link must
       remove routes pointing to the failed link immediately from the
       RIB, remove associated labels from their LIB and LFIB tabels, and
       must send LDP label withdraw(s) to their upstream LSRs.

   c.  [U2, U, V, Y] - link failed, but at least one ECMP or alternate
       path remains - AN/AGN1x node must stop using the failed link and
       immediately switchover (local-repair) to the remaining ECMP path
       or alternate path.  AN/AGN1x must remove affected next-hops and



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       labels from its tables and invoke LDP label withdraw as per point
       (a) above.  If there is an AGN1x node terminating the failed
       link, it must remove routes pointing to the failed link
       immediately from the RIB, remove associated labels from their LIB
       and LFIB tabels, and must propagate the failure on the network
       side using BGP-LU and/or core IGP procedures.

   If access IGP is used AN/AGN1x link failure will be propagated via
   IGP link updates across the access topology.

   LDP DoD will also propagate the link failure by sending label
   withdraws to upstream AN/AGN1x nodes, and label release messages
   downstream AN/AGN1x nodes.

3.5.4.  AGN Node Failure

   AGN1x fails and all links to adjacent access nodes go down.

   Depending on the access topology, following cases apply to the
   network operation after AGN1x node failure (topology references from
   Section 2 in square brackets):

   a.  [I1, I] - ANs are isolated from the network - AN adjacent to the
       failure must remove routes pointing to the failed AGN1x node
       immediately from the RIB, remove associated labels from their LIB
       and LFIB tabels, and must send LDP label withdraw(s) to their
       upstream LSRs.  If access IGP is used, an IGP link update should
       be sent.

   b.  [U2, U, V, Y] - at least one ECMP or alternate path remains - AN
       adjacent to failed AGN1x must stop using the failed link and
       immediately switchover (local-repair) to the remaining ECMP path
       or alternate path.  AN must remove affected routes and labels
       from its tables and invoke LDP label withdraw as per point (a)
       above.

   Network side procedures for handling AGN1x node failure have been
   described in Seamless MPLS [I-D.ietf-mpls-seamless-mpls].

3.5.5.  AGN Network-side Reachability Failure

   AGN1x loses network reachability to a specific destination or set of
   network-side destinations.

   In such event AGN1x must send LDP Label Withdraw messages to its
   upstream ANs, withdrawing labels for all affected /32 FECs.  Upon
   receiving those messages ANs must remove those labels from their LIB
   and LFIB tables, and use alternative LSPs instead if available as



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   part of global-repair.  In turn ANs should also sent Label Withdraw
   messages for affected /32 FECs to their upstream ANs.

   If access IGP is used, and AGN1x gets completely isolated from the
   core network, it should stop advertising the default route 0/0 into
   the access IGP.


4.  LDP DoD Procedures

   Label Distribution Protocol is specified in [RFC5036], and all LDP
   Downstream-on-Demand implementations MUST follow this specification.

   In the MPLS architecture [RFC3031], network traffic flows from
   upstream to downstream LSR.  The use cases in this document rely on
   the downstream assignment of labels, where labels are assigned by the
   downstream LSR and signaled to the upstream LSR as shown in Figure 7.

                   +----------+      +------------+
                   | upstream |      | downstream |
             ------+   LSR    +------+    LSR     +----
         traffic   |          |      |            |  address
         source    +----------+      +------------+  (/32 for IPv4)
                                                     traffic
                  label distribution for IPv4 FEC    destination
                    <-------------------------

                           traffic flow
                    ------------------------->

                 Figure 7: LDP label assignment direction

4.1.  LDP Label Distribution Control and Retention Modes

   LDP protocol specification [RFC5036] defines two modes for label
   distribution control, following the definitions in MPLS architecture
   [RFC3031]:

   o  Independent mode - an LSR recognizes a particular FEC and makes a
      decision to bind a label to the FEC independently from
      distributing that label binding to its label distribution peers.
      A new FEC is recognized whenever a new route becomes valid on the
      LSR.

   o  Ordered mode - an LSR binds a label to a particular FEC if it is
      the egress router for that FEC or if it has already received a
      label binding for that FEC from its next-hop LSR for that FEC.




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   Using independent label distribution control with LDP DoD and access
   static routing will prevent the access LSRs from propagating label
   binding failure along the access topology, making it impossible to
   switchover to an alternate path, even if such a path exists.

   LDP protocol specification [RFC5036] defines two modes for label
   retention, following the definitions in MPLS architecture [RFC3031]:

   o  Liberal mode - LSR retains every label mappings received from a
      peer LSR, regardless of whether the peer LSR is the next-hop for
      the advertised mapping.  This mode allows for quicker adaptation
      to routing changes.

   o  Conservative mode - LSR retains advertised label mappings only if
      they will be used to forward packets, that is only if they are
      received from a valid next-hop LSR according to routing.  This
      mode allows LSR to maintain fewer labels, but slows down LSR
      adaptation to routing changes.

   Using conservative label retention mode with LDP DoD will prevent the
   access LSRs (AN and AGN1x nodes) from implementing IPFRR LFA
   alternate based local-repair, as label mapping request can not be
   sent to alternate next-hops.

   Adhering to the overall design goals of Seamless MPLS
   [I-D.ietf-mpls-seamless-mpls], specifically achieving a large network
   scale without compromising fast service restoration, all access LSRs
   (AN and AGN1x nodes) MUST use LDP DoD advertisement mode with:

   o  Ordered label distribution control - enables propagation of label
      binding failure within the access topology.

   o  Liberal label retention - enables pre-programming of alternate
      next-hops with associated FEC labels.

   In Seamless MPLS [I-D.ietf-mpls-seamless-mpls] AGN1x node acts as an
   access ABR connecting access and metro domains.  To enable failure
   propagation between those domains, access ABR MUST implement ordered
   label distribution control when redistributing access static routes
   and/or access IGP routes into the network-side BGP labeled unicast
   [RFC3107] or core IGP with LDP Downstream Unsolicited label
   advertisement.

4.2.  IPv6 Support

   Current LDP protocol specification [RFC5036] defines procedures and
   messages for exchanging FEC-label bindings over IPv4 and/or IPv6
   networks.  However number of IPv6 usage areas are not clearly



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   specified including: packet to LSP mapping for IPv6 destination
   router, no IPv6 specific LSP identifier, no LDP discovery using IPv6
   multicast address, separate LSPs for IPv4 and IPv6, and others.

   All of these issues and more are being addressed by
   [I-D.ietf-mpls-ldp-ipv6] that will update LDP protocol specification
   [RFC5036] in respect to the IPv6 usage.  For the future deployment,
   LDP DoD use case and procedures described in this document SHOULD
   also support IPv6 for transport and services.

4.3.  LDP DoD Session Negotiation

   Access LSR/ABR should propose the Downstream-on-Demand label
   advertisement by setting "A" value to 1 in the Common Session
   Parameters TLV of the Initialization message.  The rules for
   negotiating the label advertisement mode are specified in LDP
   protocol specification [RFC5036].

   To establish a Downstream-on-Demand session between the two access
   LSR/ABRs, both should propose the Downstream-on-Demand label
   advertisement mode in the Initialization message.  If the access LSR
   only supports LDP DoD and the access ABR proposes Downstream
   Unsolicited mode, the access LSR SHOULD send a Notification message
   with status "Session Rejected/Parameters Advertisement Mode" and then
   close the LDP session as specified in LDP protocol specification
   [RFC5036].

   If an access LSR is acting in an active role, it should re-attempt
   the LDP session immediately.  If the access LSR receives the same
   Downstream Unsolicited mode again, it should follow the exponential
   backoff algorithm as defined in the LDP protocol specification
   [RFC5036] with delay of 15 seconds and subsequent delays growing to a
   maximum delay of 2 minutes.

   In case a PWE3 service is required between the adjacent access LSR/
   ABR, and LDP DoD has been negotiated for IPv4 and IPv6 FECs, the same
   LDP session should be used for PWE3 FECs.  Even if LDP DoD label
   advertisement has been negotiated for IPv4 and IPv6 LDP FECs as
   described earlier, LDP session should use Downstream Unsolicited
   label advertisement for PWE3 FECs as specified in PWE3 LDP [RFC4447].

4.4.  Label Request Procedures

4.4.1.  Access LSR/ABR Label Request

   Upstream access LSR/ABR will request label bindings from adjacent
   downstream access LSR/ABR based on the following trigger events:




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   a.  Access LSR/ABR is configured with /32 static route with LDP DoD
       label request policy in line with intitial network setup use case
       described in Section 3.1.

   b.  Access LSR/ABR is configured with a service in line with service
       use cases described in Section 3.2 and Section 3.3.

   c.  Access LSR/ABR link to adjacent node comes up and LDP DoD session
       is established.  In this case access LSR should send label
       request messages for all /32 static routes configured with LDP
       DoD policy and all /32 routes related to provisioned services
       that are not covered by default route.  In line with use cases
       described in Section 3.5.

   d.  In all above cases requests MUST be sent to next-hop LSR(s) and
       alternate LSR(s).

   Downstream access LSR/ABR will respond with label mapping message
   with a non-null label if any of the below conditions are met:

   a.  Downstream access LSR/ABR - requested FEC is an IGP or static
       route and there is an LDP label already learnt from the next-
       next-hop downstream LSR (by LDP DoD or LDP DU).  If there is no
       label for the requested FEC and there is an LDP DoD session to
       the next-next-hop downstream LSR, downstream LSR MUST send a
       label request message for the same FEC to the next-next-hop
       downstream LSR.  In such case downstream LSR will respond back to
       the requesting upstream access LSR only after getting a label
       from the next-next-hop downstream LSR peer.

   b.  Downstream access ABR only - requested FEC is a BGP labelled
       unicast route [RFC3107] and this BGP route is the best selected
       for this FEC.

   Downstream access LSR/ABR may respond with a label mapping with
   explicit-null or implicit-null label if it is acting as an egress for
   the requested FEC, or it may respond with "No Route" notification if
   no route exists.

4.4.2.  Label Request Retry

   If an access LSR/ABR receives a "No route" Notification in response
   to its label request message, it should retry using an exponential
   backoff algorithm similar to the backoff algoritm mentioned in the
   LDP session negotiation described in Section 4.3.

   If there is no response to the sent label request message, the LDP
   specification [RFC5036] (section A.1.1, page# 100) states that the



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   LSR should not send another request for the same label to the peer
   and mandates that a duplicate label request is considered a protocol
   error and should be dropped by the receiving LSR by sending a
   Notification message.

   Thus, if there is no response from the downstream peer, the access
   LSR/ABR should not send a duplicate label request message again.

   If the static route corresponding to the FEC gets deleted or if the
   DoD request policy is modified to reject the FEC before receiving the
   label mapping message, then the access LSR/ABR should send a Label
   Abort message to the downstream LSR.

4.4.3.  Label Request with Fast-Up Convergence

   In some conditions, the exponential backoff algorithm usage described
   in Section 4.4.2 may result in a longer than desired wait time to get
   a successful LDP label to route mapping.  An example is when a
   specific route is unavailable on the downstream LSR when the label
   mapping request from the upstream is received, but later comes back.
   In such case using the exponential backoff algorithm may result in a
   max delay wait time before the upstream LSR sends another LDP label
   request.

   Fast-up convergence can be addressed with a minor extension to the
   LDP DoD procedure, as described in this section.  The downstream and
   upstream LSRs SHOULD implement this extension if up convergence
   improvement is desired.

   The extension consists of the upstream LSR indicating to the
   downstream LSR that the label request should be queued on the
   downstream LSR until the requested route is available.

   To implement this behavior, a new Optional Parameter is defined for
   use in the Label Request message:

                 Optional Parameter      Length     Value
                 Queue Request TLV         0      see 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|0|  Queue Request (0x????)   |         Length (0x00)         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      U-bit = 1
         Unknown TLV bit is set to 1. If this optional TLV is unknown,
         it should be ignored without sending "no route" notification.
         Ensures backward compatibility.

      F-bit = 0
         Forward unknown TLV bit is set to 0. The unknown TLV is not
         forwarded.

      Type
         Queue Request Type value to be allocated by IANA.

      Length = 0x00
         Specifies the length of the Value field in octets.

   The operation is as follows.

   To benefit from the fast-up convergence improvement, the upstream LSR
   sends a Label Request message with a Queue Request TLV.

   If the downstream LSR supports the Queue Request TLV, it verifies if
   route is available and if so it replies with label mapping as per
   existing LDP procedures.

   If the route is not available, the downstream LSR queues the request
   and replies as soon as the route becomes available.  In the meantime,
   it does not send a "no route" notification back.  When sending a
   label request with the Queue Request TLV, the upstream LSR does not
   retry the Label Request message if it does not receive a reply from
   its downstream peer

   If the upstream LSR wants to abort an outstanding label request while
   the Label Request is queued in the downstream LSR, the upstream LSR
   sends a Label Abort Request message, making the downstream LSR to
   remove the original request from the queue and send back a
   notification Label Request Aborted [RFC5036].

   If the downstream LSR does not support the Queue Request TLV, it will
   silently ignores it, and sends a "no route" notification back.  In
   this case the upstream LSR invokes the exponential backoff algorithm
   described in Section 4.4.2.




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   This described procedure ensures backward compatitibility.

4.5.  Label Withdraw

   If an MPLS label on the downstream access LSR/ABR is no longer valid,
   the downstream access LSR/ABR withdraws this FEC/label binding from
   the upstream access LSR/ABR with the Label Withdraw Message [RFC5036]
   with a specified label TLV or with an empty label TLV.

   Downstream access LSR/ABR SHOULD withdraw a label for specific FEC in
   the following cases:

   a.  If LDP DoD ingress label is associated with an outgoing label
       assigned by BGP labelled unicast route, and this route is
       withdrawn.

   b.  If LDP DoD ingress label is associated with an outgoing label
       assigned by LDP (DoD or DU) and the IGP route is withdrawn from
       the RIB or downstream LDP session is lost.

   c.  If LDP DoD ingress label is associated with an outgoing label
       assigned by LDP (DoD or DU) and the outgoing label is withdrawn
       by the downstream LSR.

   d.  If LDP DoD ingress label is associated with an outgoing label
       assigned by LDP (DoD or DU), route next-hop changed and

       *  there is no LDP session to the new next-hop.  To minimize
          probability of this, the access LSR/ABR should implement LDP-
          IGP synchronization procedures as specified in [RFC5443].

       *  there is an LDP session but no label from downstream LSR.  See
          note below.

   e.  If access LSR/ABR is configured with a policy to reject exporting
       label mappings to upstream LSR.

   The upstream access LSR/ABR responds to the Label Withdraw Message
   with the Label Release Message [RFC5036].

   After sending label release message to downstream access LSR/ABR, the
   upstream access LSR/ABR should resend label request message, assuming
   upstream access LSR/ABR still requires the label.

   Downstream access LSR/ABR should withdraw a label if the local route
   configuration (e.g. /32 loopback) is deleted.

   Note: For any events inducing next hop change, downstream access LSR/



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   ABR should attempt to converge the LSP locally before withdrawing the
   label from an upstream access LSR/ABR.  For example if the next-hop
   changes for a particular FEC and if the new next-hop allocates labels
   by LDP DoD session, then the downstream access LSR/ABR must send a
   label request on the new next-hop session.  If downstream access LSR/
   ABR doesn't get label mapping for some duration, then and only then
   downstream access LSR/ABR must withdraw the upstream label.

4.6.  Label Release

   If an access LSR/ABR does not need any longer a label for a FEC, it
   sends a Label Release Message [RFC5036] to the downstream access LSR/
   ABR with or without the label TLV.

   If upstream access LSR/ABR receives an unsolicited label mapping on
   DoD session, they should release the label by sending label release
   message.

   Access LSR/ABR should send a label release message to the downstream
   LSR in the following cases:

   a.  If it receives a label withdraw from the downstream access LSR/
       ABR.

   b.  If the /32 static route with LDP DoD label request policy is
       deleted.

   c.  If the service gets decommissioned and there is no corresponding
       /32 static route with LDP DoD label request policy configured.

   d.  If the route next-hop changed, and the label does not point to
       the best or alternate next-hop.

   e.  If it receives a label withdraw from a downstream DoD session.

4.7.  Local Repair

   To support local-repair with ECMP and IPFRR LFA, access LSR/ABR MUST
   request labels on both best next-hop and alternate next-hop LDP DoD
   sessions as specified in the label request procedures in Section 4.4.
   This will enable access LSR/ABR to pre-program the alternate
   forwarding path with the alternate label(s), and invoke IPFRR LFA
   switch-over procedure if the primary next-hop link fails.


5.  IANA Considerations





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5.1.  LDP TLV TYPE

   This document uses a new a new Optional Parameter Queue Request TLV
   in the Label Request message defined in Section 4.4.3.  IANA already
   maintains a registry of name LDP "TLV TYPE NAME SPACE" defined by
   RFC5036.  The following value is suggested for assignment:

                         TLV type  Description
                         0x0971    Queue Request TLV


6.  Security Considerations


7.  Acknowledgements

   The authors would like to thank Nischal Sheth, Nitin Bahadur, Nicolai
   Leymann and Ina Minei for their suggestions and review.


8.  References

8.1.  Normative References

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

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

8.2.  Informative References

   [I-D.ietf-mpls-ldp-ipv6]
              Asati, R., Manral, V., Papneja, R., and C. Pignataro,
              "Updates to LDP for IPv6", draft-ietf-mpls-ldp-ipv6-05
              (work in progress), August 2011.

   [I-D.ietf-mpls-seamless-mpls]
              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M., and D. Steinberg, "Seamless MPLS Architecture",
              draft-ietf-mpls-seamless-mpls-00 (work in progress),
              May 2011.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, May 2001.



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   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

   [RFC4446]  Martini, L., "IANA Allocations for Pseudowire Edge to Edge
              Emulation (PWE3)", BCP 116, RFC 4446, April 2006.

   [RFC4447]  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.

   [RFC5283]  Decraene, B., Le Roux, JL., and I. Minei, "LDP Extension
              for Inter-Area Label Switched Paths (LSPs)", RFC 5283,
              July 2008.

   [RFC5443]  Jork, M., Atlas, A., and L. Fang, "LDP IGP
              Synchronization", RFC 5443, March 2009.


Authors' Addresses

   Thomas Beckhaus
   Deutsche Telekom AG
   Heinrich-Hertz-Strasse 3-7
   Darmstadt,   64307
   Germany

   Phone: +49 6151 58 12825
   Fax:
   Email: thomas.beckhaus@telekom.de
   URI:


   Bruno Decraene
   France Telecom
   38-40 rue du General Leclerc
   Issy Moulineaux cedex 9,   92794
   France

   Phone:
   Fax:
   Email: bruno.decraene@orange.com
   URI:









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   Kishore Tiruveedhula
   Juniper Networks
   10 Technology Park Drive
   Westford, Massachusetts  01886
   USA

   Phone: 1-(978)-589-8861
   Fax:
   Email: kishoret@juniper.net
   URI:


   Maciek Konstantynowicz
   Juniper Networks


   Phone:
   Fax:
   Email: maciek@juniper.net
   URI:


   Luca Martini
   Cisco Systems, Inc.
   9155 East Nichols Avenue, Suite 400
   Englewood, CO  80112
   USA

   Phone:
   Fax:
   Email: lmartini@cisco.com
   URI:



















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