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Network Working Group                             Albert J. Tian
Internet Draft                                    Naiming Shen
Expiration Date: Jan 2005                         Redback Networks
                                                  July 2004

              Loose Segment Optimization in Explicit Paths

                  draft-tian-rsvp-loose-seg-opt-00.txt


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



2. Abstract

   RSVP-TE [RSVPTE] can signal explicit paths with loose or strict hops
   in a MPLS network. Using loose hops can shorten the ERO, but can not
   reduce the overhead associated with an RSVP signaled LSP since path
   states are still created on every hop along the path.

   In this paper, we propose a mechanism that can reduce the signaling
   and maintenance overhead associated with loose hops in an RSVP
   signaled LSP in an LDP enabled network. The mechanism can also be
   generalized to work with other tunneling technologies such as GRE or
   IP-in-IP.






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3. Introduction

   A loose hop in an explicit path means the actual path for that loose
   segment is not pre-determined and may traverse one or more
   intermediate nodes. In many cases where the the ERO is the only
   requirement, the path is determined by routing.

   LDP on the other hand builds LSPs that follow routing. This means the
   actual path for a loose segment in some explicitly path will be the
   same as that of an LDP LSP whose egress matches prefix specified in
   the loose hop.

   If the LDP LSP can satisfy the requirement of the RSVP loose hop, in
   other words, the RSVP LSP does not have QoS or other requirements,
   then we can optimize the RSVP LSP by tunneling control and data
   traffic directly from the starting node to the ending node of the
   loose segment through an LDP LSP.

   Forming Forwarding Adjacency out of a TE LSP and nesting other LSPs
   into the TE LSP by using label stack construct is a well established
   concept in GMPLS [HIER-LSP]. Here we are essentially proposing to
   form "Soft Forwarding Adjacencies" (Soft FAs) out of LDP LSPs and
   establish RSVP LSPs across LDP LSPs using label stacking. Soft FAs
   are similar to FAs in that they can be treated as a link to forward
   control and data traffic. They are different from the FAs in that
   they are more dynamic, do not have QoS guarantees, and are not
   advertised to ISIS/OSPF component for path computation.

   It is also possible to form soft FAs over other tunneling
   technologies such as GRE or IP-in-IP instead of LDP LSPs. The
   mechanism is essentially the same.

   Since LDP LSPs and GRE or IP-in-IP tunnels do not support resource
   reservation, RSVP LSPs nested inside soft FAs usually can not
   support resource reservation.

   One primary application of the loose hop optimization is in the area
   of IP/LDP fast re-route. RSVP-TE can be used to signal a repair path
   to protect IP/LDP destinations from link or node failures. Since
   there is in general no QoS requirement on the original traffic, there
   is also no QoS requirement on the repair paths. To protect the
   network from all possible node or link failures, a large number of
   repair paths need to be established. Therefore it is very important
   to reduce the per repair path overhead. The loose segment
   optimization can achieve just that.






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4. RSVP Extensions

   A new flag in Session Attribute Object is introduced to indicate
   Loose Hop Optimization using Soft FAs is desired.

   The Session Attribute Object is defined in section 4.7 of [RSVPTE].

      Flags

         0x10  O-bit. Loose Hop Optimization desired.

            This flag indicates that Loose Hop Optimization using soft
            FAs is desired.


5.  Conditions for Optimization

   The optimization is performed at the starting and ending node of a
   loose segment.

   The starting node of a loose segment in an explicit path is the first
   node that evaluates the corresponding loose subobject in the ERO.

   The ending node of a loose segment in an explicit path is the node
   that contains the prefix in the corresponding subobject in the ERO,
   or is the egress node of the explicit path.

   When the starting node of a loose segment evaluates the corresponding
   subobject in the ERO, if all of the following conditions hold, then
   the loose hop optimization can be performed:

    1) The LSP Optimization Object is present in the PATH message and
       the O-bit is set,
    2) There is an active soft FA whose egress is the exact match for
       the nexthop address, which is either the prefix in the
       corresponding subobject in the ERO, or the egress address of the
       RSVP LSP.
    3) The matching soft FA satisfies all the requirements of the RSVP
       LSP.
    4) The matching soft FA satisfies a minimum span requirement set in
       local configuration.










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6. Optimization for a Loose Segment


6.1. Head End Node of the RSVP LSP

   When the head end of an RSVP LSP wants to optimize the loose segment
   using LDP LSP, then it SHOULD include the LSP Optimization Object in
   the PATH message with the O-bit set.


6.2. Starting Node of a Loose Segment

   Any node along the explicit path that evaluates a loose subobject may
   initiate the loose segment optimization if all the conditions in
   section 5 hold.

   The optimization can be done in the following steps:

   1)  The RSVP module can query the local registry to obtain
       information regarding the matching soft FA.

       If LDP LSPs are used as soft FAs, the query would return
       the matching LDP LSP.

       If GRE or IP-in-IP tunnels are used as soft FAs, the query would
       return the matching GRE or IP-in-IP tunnels. The tunnels could
       be pre-established or could be established on demand.

   2)  Standard RSVP mechanisms for handling tunnels should be used to
       handle signaling over soft FAs. The PATH messages are tunneled
       directly to the ending node of the loose segment through
       matching matching soft FA. The PATH message MUST have the Router
       Alert option so that it can be processed by the egress node of
       the soft FA. The PATH message should include RSVP HOP object.
       Since soft FAs may not have logical interfaces associated with
       them, the previous hop address in the RSVP HOP object should be
       set to any reachable interface address(router-Id or loopback
       interface addresses are preferred). The Logical Interface Handle
       may be zero or may identify the soft FA.

   3)  The action associated with the locally allocated RSVP label
       should be swap and the resulting data packets need to be
       tunneled directly to the egress of the soft FA.

       If LDP LSPs are used as soft FAs, the label operation for the
       RSVP LSP should be swap and push to form a label stack with RSVP
       label as the inner label and LDP label as the outer label.




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       If GRE or IP-in-IP tunnels are used as soft FAs, the RSVP
       labeled packets will be encapsulated in GRE or IP-in-IP header
       and tunneled directly to the ending node of the loose segment.

   If any of the conditions listed above in section 5 fails to hold,
   then the optimization should not be activated and the RSVP PATH
   message should be forwarded downstream hop by hop as usual.


6.3. Ending Node of a Loose Segment

   For the ending node of a loose segment, PATH messages may arrive on a
   soft FA. In this case, it should send the RESV message directly to
   the RSVP HOP which may be multiple hops away.

   Traffic for the RSVP LSP may arrive on an soft FA. The RSVP labeled
   packet should be processed as normal.

   If LDP LSPs are used as soft FAs, the outer LDP label will be popped
   (may be popped on the penultimate hop) and the inner RSVP label will
   be processed accordingly.

   If GRE or IP-in-IP tunnels are used as soft FAs, the packets will be
   decapsulated and then forwarded based on the RSVP label.

   The ending node of a loose segment may be the starting node of
   another loose segment, where the same optimization process can repeat
   again.


6.4. Tail End Node of the RSVP LSP

   The tail end node of the RSVP LSP may support PHP and advertise
   implicate null label to the RSVP HOP. In this case traffic on the
   last loose segment may not contain any RSVP label.

   If LDP LSPs are used as soft FAs, then over the last loose segment,
   packets only contain the LDP label. Effectively the RSVP LSP merges
   into the LDP LSP.


6.5. Minimum Tunnel Span

   Each node should impose a minimum tunnel span requirement on the soft
   FAs to avoid using one hop soft FAs for the optimization.

   If LDP LSPs are used as soft FAs, then the ingress of the LSP may
   tell whether it is a one hop LSP by looking at the outgoing label.



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   One hop LSPs have either implicit null or explicit null label as
   outgoing labels.

   Also the LDP ADDRESS message will list all interface addresses that
   belong to a given neighbor. If the LSP egress matches any of those
   addresses, then the LSP is a one hop LSP.

   If GRE or IP-in-IP tunnels are used as soft FAs, the tunnel length
   can be derived from the Traffic Engineering Database. Also tools such
   as traceroute can be used to determine the tunnel length.


7. Loose Segment Optimization in P2MP Traffic Engineering

   The same optimization can also apply to P2MP traffic engineering, if
   the point to multi-point LSPs do not have QoS requirements [P2MP-
   LSP1] [P2MP-LSP2].

   The PATH messages for P2MP LSP setup can be tunneled to the next set
   of branching points through soft FAs, and RESV messages can be sent
   back to the node where the branches join.

   Data packets can be replicated at the branching points, then tunneled
   to the next set of branching points through soft FAs.


8. Security Considerations

   This document does not introduce any new security issues.


9. IANA Considerations

   TBD


10. Full Copyright Statement

   Copyright (C) The Internet Society (2002). All Rights Reserved.
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the  purpose of



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   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


11. References

    [RSVPTE] Awduche, et al., "Extensions to RSVP for LSP Tunnels",
    RFC 3209, December 2001.

    [LDP] L. Andersson, P. Doolan, N. Feldman, A. Fredette, and B.
    Thomas, "LDP Specification", RFC 3036, January 2001.

    [HIER-LSP] K. Kompella, Y. Rekhter, "LSP Hierarchy with Generalized
    MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, March 2002, work in
    progress.

    [P2MP-LSP1] R. Aggarwal, et al., "Establishing Point to Multipoint
    MPLS TE LSPs", draft-raggarwa-mpls-p2mp-te-01.txt, Work In
    Progress.

    [P2MP-LSP2] S. Yasukawa, et al., "Extended RSVP-TE for
    Point-to-Multipoint LSP Tunnels",
    draft-yasukawa-mpls-rsvp-p2mp-04.txt, Work In Progress.
















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12. Author Information


   Albert Jining Tian
   Redback Networks, Inc.
   300 Holger Way
   San Jose, CA 95134
   Email: tian@redback.com

   Naiming Shen
   Redback Networks, Inc.
   300 Holger Way
   San Jose, CA 95134
   Email: naiming@redback.com





































Tian & Shen                                                     [Page 8]


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