Network Working Group                                        R. Aggarwal
Internet Draft                                          Juniper Networks
Expiration Date: May 20, 2008
                                                           J. L. Le Roux
                                                          France Telecom

                                                       November 17, 2007

               MPLS Upstream Label Assignment for RSVP-TE


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   This document describes procedures for distributing upstream-assigned
   labels for Resource Reservation Protocol - Traffic Engineering (RSVP-
   TE).  It also describes how these procedures can be used for avoiding
   branch LSR traffic replication on a LAN for RSVP-TE point-to-
   multipoint (P2MP)LSPs.

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Table of Contents

 1          Specification of requirements  .........................   2
 2          Introduction  ..........................................   2
 3          RSVP-TE Upstream Label Assignment Capability  ..........   3
 4          Distributing Upstream-Assigned Labels in RSVP-TE  ......   4
 4.1        Procedures  ............................................   4
 5          RSVP-TE Tunnel Identifier Exchange  ....................   5
 6          RSVP-TE Point-to-Multipoint LSPs on a LAN  .............   6
 7          Acknowledgements  ......................................   7
 8          References  ............................................   7
 8.1        Normative References  ..................................   7
 8.2        Informative References  ................................   8
 9          Author Information  ....................................   8
10          Intellectual Property Statement  .......................   8
11          Full Copyright Statement  ..............................   9

1. Specification of requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2. Introduction

   This document describes procedures for distributing upstream-assigned
   labels [MPLS-UPSTREAM] for Resource Reservation Protocol with Traffic
   Engineering (RSVP-TE). These procedures follow the architecture for
   MPLS Upstream Label Assignment described in [MPLS-UPSTREAM].

   This document describes extensions to RSVP-TE that a LSR can use to
   advertise to its neighboring LSRs whether the LSR supports upstream
   label assignment.

   This document also describes extensions to RSVP-TE to distribute
   upstream-assigned labels.

   The usage of MPLS upstream label assignment using RSVP-TE for

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   avoiding branch LSR [RSVP-P2MP] traffic replication on a LAN for
   RSVP-TE P2MP TE LSPs [RSVP-TE-P2MP] is also described.

3. RSVP-TE Upstream Label Assignment Capability

   According to [MPLS-UPSTREAM], upstream-assigned label bindings MUST
   NOT be used unless it is known that a downstream LSR supports them.
   This implies that there MUST be a mechanism to enable a LSR to
   advertise to its RSVP-TE neighbor LSR(s) its support of upstream-
   assigned labels.

   [RSVP-RESTART] defines a CAPABILITY object to be carried within Hello
   messages, and used to indicate the set of capabilities supported by a
   node. Currently one flag is defined, the R flag indicating the
   support for RecoveryPath Srefresh. This document defines a new flag,
   the U flag, to signal a LSR's support of upstream label assignment to
   its RSVP-TE neighbors.

   The format of a Capability object 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
      |            Length             | Class-Num(TBA)|  C-Type  (1)  |
      |                         Reserved                          |U|R|

   Recovery Path Srefresh Capable (R): 1 bit, defined in [RSVP-RESTART].

   Upstream Label Assignement Capable (U): 1 bit When set this means
   that the LSR is capable of both distributing upstream-assigned label
   bindings and receiving upstream-assigned label bindings

   Reserved bits MUST be set to zero on transmission and MUST be ignored
   on receipt.

   The usage of RSVP-TE Hello messages for exchanging upstream label
   assignment capability implies that a LSR MAY exchange RSVP-TE Hellos
   with a neighbor before sending/receiving any other RSVP-TE messages
   to/from that neighbor.

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4. Distributing Upstream-Assigned Labels in RSVP-TE

   An optional RSVP-TE object, the UPSTREAM_ASSIGNED_LABEL object is
   introduced to signal an upstream-assigned label. The Class-Num for
   this object comes from the 0bbbbbbb space and is to be determined by


       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
      |                      Reserved                                 |
      |                        Label                                  |
      |                          ....                                 |

   The label can be encoded as in [RFC3209] when the C-Type is 1 or as a
   Generalized Label [RFC3473] when the C-Type is 2 or 3.

4.1. Procedures

   A RSVP-TE LSR that assigns Upstream-Assigned Labels, distributes them
   to the downstream LSRs by including them in RSVP-TE Path messages.

   to a downstream LSR if the downstream LSR had not previously
   advertised the CAPABILITY object with the U bit set in its RSVP-TE
   Hello messages.

   If a downstream RSVP-TE LSR receives a Path message that carries an
   UPSTREAM_ASSIGNED_LABEL Object and the LSR does not support the
   object C-Num/C-Type it will return an "Unknown Object C-Num/C-Type"
   error. If the LSR does support the object, but is unable to process
   the upstream-assigned label as described in [MPLS-UPSTREAM] it SHOULD
   send a PathErr with the error code "Routing problem" and the error
   value "MPLS Upstream Assigned Label Processing Failure". If the LSR
   successfully processes the Path message and the upstream-assigned
   label it MUST send a Resv message upstream as per [RFC3209] but it
   MUST NOT include the LABEL object with a downstream assigned label in
   the Resv Message. This is because as described in [MPLS-UPSTREAM] two
   LSRs Ru and Rd for a LSP that is bound to FEC F, MUST use either
   downstream-assigned label distribution or upstream-assigned label
   distribution,for FEC F, but NOT both, for packets that are to be
   transmitted on the LSP from Ru to Rd.

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5. RSVP-TE Tunnel Identifier Exchange

   As described in [MPLS-UPSTREAM] an upstream LSR Ru MAY transmit a
   MPLS packet, the top label of which (L) is upstream-assigned, to a
   downstream LSR Rd, by encapsulating it in an IP or MPLS tunnel. In
   this case the fact that L is upstream-assigned is determined by Rd by
   the tunnel on which the packet is received. There must be a mechanism
   for Ru to inform Rd that a particular tunnel from Ru to Rd will be
   used by Ru for transmitting MPLS packets with upstream-assigned MPLS

   When RSVP-TE is used for upstream label assignment, the IF_ID
   RSVP_HOP object is used for signaling the Tunnel Identifier. If Ru
   uses an IP or MPLS tunnel to transmit MPLS packets with upstream
   assigned labels to Rd, Ru MUST include the IF_ID RSVP_HOP object
   [RFC3473] in Path messages along with the UPSTREAM_ASSIGNED_LABEL

   Three new TLVs are introduced in the IF_ID RSVP_HOP object [RFC3471]
   to support RSVP-TE P2MP LSPs, IP Multicast Tunnels and context
   labels.  The TLV value acts as the tunnel identifier.

   1. RSVP-TE P2MP LSP TLV. Type = TBD. Value of the TLV is the RSVP-TE
   P2MP Session Object and optionally the P2MP Sender Template Object
   [RSVP-TE-P2MP].  The TLV value identifies the RSVP-TE P2MP LSP.  This
   mechanism extends RSVP-TE P2P Hierarchy [LSP-HIER] to RSVP-TE P2MP
   Hierarchy. It allows Ru to tunnel an "inner" P2MP LSP, the label for
   which is upstream assigned, over an "outer" P2MP LSP that has leaves
   <Rd1...Rdn>. The P2MP LSP IF_ID TLV allows Ru to signal to
   <Rd1...Rdn> the binding of the inner P2MP LSP to the outer P2MP LSP.
   The control plane signaling between Ru and <Rd1...Rdn> for the inner
   P2MP LSP uses directed RSVP-TE signaling messages as in [LSP-HIER].

   2. IP Multicast Tunnel TLV. Type = TBD. In this case the TLV value is
   a <Source Address, Multicast Group Address> tuple. Source Address is
   the IP address of the root of the tunnel i.e. Ru, and Multicast Group
   Address is the Multicast Group Address used by the tunnel.

   3. MPLS Context Label TLV. Type = TBD. In this case the TLV value is
   a <Source Address, MPLS Context Label> tuple. The Source Address
   belongs to Ru and the MPLS Context Label is an upstream assigned
   label, assigned by Ru. This allows Ru to tunnel an "inner" RSVP-TE
   P2MP LSP, the label of which is upstream assigned, over an "outer"
   MPLS LSP, where the outer LSP has the following property:

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     + The label pushed by Ru for the outer MPLS LSP is an upstream
       assigned context label, assigned by Ru. When <Rd1...Rdn> perform
       a MPLS label lookup on this label a combination of this label and
       the incoming interface MUST be sufficient for <Rd1...Rdn> to
       uniquely determine Ru's context specific label space to lookup
       the next label on the stack in. <Rd1...Rdn> MUST receive the data
       sent by Ru with the context specific label assigned by Ru being
       the top label on the label stack.

   Currently the usage of the context label TLV is limited only to RSVP-
   TE P2MP LSPs on a LAN as specified in the next section. The context
   label TLV MUST NOT be used for any other purposes.

6. RSVP-TE Point-to-Multipoint LSPs on a LAN

   This section describes one application of upstream label assignment
   using RSVP-TE. Further applications are to be described in separate

   [RSVP-TE-P2MP] describes how to setup RSVP-TE P2MP LSPs. On a LAN the
   solution described in [RSVP-TE-P2MP] relies on "ingress replication".
   A LSR on a LAN (say Il), that is a branch LSR for a P2MP LSP, (say
   Ru) sends a separate copy of a packet that it receives on the P2MP
   LSP to each of the downstream LSRs on the LAN (say <Rd1...Rdn> that
   are adjacent to it in the P2MP LSP.

   In order to increase efficiency of bandwidth utilization, it is
   desirable for Ru to send a single copy of the packet for the P2MP LSP
   on the LAN, when there are multiple downstream routers on the LAN
   that are adjacent in that P2MP LSP. This requires that each of
   <Rd1...Rdn> must be able to associate the label L, used by Ru to
   transmit packets for the P2MP LSP on the LAN, with that P2MP LSP. It
   is possible to achieve this using RSVP-TE upstream-assigned labels
   with the following procedures. Assume that Ru and <Rd1...Rdn> support
   upstream label assignment.

   Ru sends a Path message for the P2MP LSP to each of <Rd1...Rdn> that
   is adjacent on the P2MP LSP, with the same UPSTREAM_ASSIGNED_LABEL
   object. This object carries an upstream assigned label, L. This
   message also carries a MPLS Context Label TLV, as described in the
   previous section, with the value of the MPLS label set to a value
   assigned by Ru on inteface I1 as specified in [MPLS-UPSTREAM].
   <Rd1...Rdn> "reserve" the upstream assigned label in the separate
   Upstream Neighbor Label Space that they maintain for Ru [MPLS-

   Ru can then transmit a single packet for the P2MP LSP to <Rd1..Rdn>

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   with a top label L using procedures defined in [MPLS-UPSTREAM] and
   [MPLS-MCAST-ENCAPS]. The MPLS packet transmitted by Ru contains as
   the top label the context label assigned by Ru on the LAN interface,
   I1. The bottom label is the upstream label assigned by Ru to the
   RSVP-TE P2MP LSP. The top label is looked up in the context of the
   LAN interface, I1, [MPLS-UPSTREAM] by a downstream LSR on the LAN.
   This lookup enables the downstream LSR to determine the context
   specific label space to lookup the inner label in.

   If a subset of <Rd1...Rdn> do not support upstream label assignment
   these procedures can still be used between Ru and the remaining
   subset of <Rd1...Rdn>. Ingress replication and downstream label
   assignment will continue to be used for LSRs that do not support
   upstream label assignment.

7. Acknowledgements

   Thanks to Yakov Rekhter for his contribution. Thanks to Ina Minei and
   Thomas Morin for their comments.

8. References

8.1. Normative References

   [RFC3031] "MPLS Architecture", E. Rosen, A. Viswanathan, R. Callon,
   RFC 3031.

   [MPLS-UPSTREAM] R. Aggarwal, Y. Rekhter, E. Rosen, "MPLS Upstream
   Label Assignment and Context Specific Label Space", draft-ietf-mpls-

   [MPLS-MCAST-ENCAPS] T. Eckert, E. Rosen, R. Aggarwal, Y. Rekhter,

   [RFC3209] Awduche et. al." "RSVP-TE: Extensions to RSVP for LSP
   Tunnels", RFC 3209, December 2001.

   [RFC2119] "Key words for use in RFCs to Indicate Requirement
   Levels.", Bradner, March 1997

   [RFC3473] Berger, L., Editor, "Generalized Multi-Protocol Label
   Switching (GMPLS) Signaling - Resource ReserVation Protocol-Traffic
   Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

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   [RFC3471] Berger, L. Editor, "Generalized Multi-Protocol Label
   Switching (GMPLS) Signaling Functional Description", RFC 3471 January

   [RSVP-RESTART] A. Satyanarayana et. al., "Extensions to GMPLS RSVP
   Graceful Restart", draft-ietf-ccamp-rsvp-restart-ext-02.txt

8.2. Informative References

   [MVPN] E. Rosen, R. Aggarwal [Editors], "Multicast in BGP/MPLS VPNs",

   [RSVP-TE-P2MP] R. Aggarwal, D. Papadimitriou, S. Yasukawa [Editors],
   "Extensions to RSVP-TE for Point to Multipoint TE LSPs", draft-ietf-

9. Author's Address

   Rahul Aggarwal
   Juniper Networks
   1194 North Mathilda Ave.
   Sunnyvale, CA 94089
   Phone: +1-408-936-2720

   Jean-Louis Le Roux
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex

10. Intellectual Property Statement

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   Copies of IPR disclosures made to the IETF Secretariat and any

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11. Full Copyright Statement

   Copyright (C) The IETF Trust (2007). This document is subject to the
   rights, licenses and restrictions contained in BCP 78, and except as
   set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an

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