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Versions: (draft-kompella-mpls-bundle) 00 01 02 03 04 05 06 RFC 4201

Network Working Group                                   Kireeti Kompella
Internet Draft                                          Juniper Networks
Expiration Date: January 2003                              Yakov Rekhter
                                                        Juniper Networks
                                                              Lou Berger
                                                          Movaz Networks

               Link Bundling in MPLS Traffic Engineering

                     draft-ietf-mpls-bundle-04.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

   For the purpose of Generalized Multi-Protocol Label Switching (GMPLS)
   signaling in certain cases a combination of <link identifier, label>
   is not sufficient to unambiguously identify the appropriate resource
   used by a Label Switched Path (LSP).  Such cases are handled by using
   the link bundling construct which is described in this document.











Kompella, K., Rekhter, Y., Berger, L.                           

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3. Specification of Requirements

   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].


4. Link Bundling

   As defined in [GMPLS-ROUTING], a TE link is a logical construct that
   represents a way to group/map the information about certain physical
   resources (and their properties) that interconnect LSRs into the
   information that is used by Constrained SPF for the purpose of path
   computation, and by GMPLS signaling.

   As further stated in [GMPLS-ROUTING], depending on the nature of
   resources that form a particular TE link, for the purpose of GMPLS
   signaling in some cases a combination of <link identifier, label> is
   sufficient to unambiguously identify the appropriate resource used by
   an LSP. In other cases, a combination of <link identifier, label> is
   not sufficient.  Such cases are handled by using the link bundling
   construct which is described in this document.

   Consider a TE link such that for the purpose of GMPLS signaling a
   combination of <link identifier, label> is not sufficient to
   unambiguously identify the appropriate resources used by an LSP.  In
   this situation the link bundling construct assumes that the set of
   resources that form the TE link could be partitioned into disjoint
   subsets, such that (a) the partition is minimal, and (b) within each
   subset a label is sufficient to unambiguously identify the
   appropriate resources used by an LSP. We refer to such subsets as
   "component links", and to the whole TE link as a "bundled link".  On
   a bundled link a combination of <(bundled) link identifier, component
   link identifier, label> is sufficient to unambiguously identify the
   appropriate resources used by an LSP.

   Since within each component link a label is sufficient to
   unambiguously identify the resources used by an LSP, one could also
   say that a component link is a TE link, and a bundled link is a
   collection of TE links.

   The partition of resources that form a bundled link into component
   links has to be done consistently at both ends of the bundled link.

   The purpose of link bundling is to improve routing scalability by
   reducing the amount of information that has to be handled by OSPF
   and/or IS-IS. This reduction is accomplished by performing
   information aggregation/abstraction. As with any other information



Kompella, K., Rekhter, Y., Berger, L.                           

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   aggregation/abstraction, this results in losing some of the
   information. To limit the amount of losses one need to restrict the
   type of the information that can be aggregated/abstracted.


4.1. Restrictions on Bundling

   All component links in a bundle must begin and end on the same pair
   of LSRs, have the same Link Type (i.e., point-to-point or multi-
   access), the same Traffic Engineering metric, and the same set of
   resource classes at each end of the links.

   A Forwarding Adjacency may be a component link; in fact, a bundle can
   consist of a mix of point-to-point links and FAs.

   If the component links are all multi-access links, the set of IS-IS
   or OSPF routers connected to each component link must be the same,
   and the Designated Router for each component link must be the same.
   If these conditions cannot be enforced, multi-access links must not
   be bundled.


4.2. Routing Considerations

   A component link may be either numbered or unnumbered. A bundled link
   may itself be numbered or unnumbered independent of whether the
   component links of that bundled link are numbered or not.

   Handling identifiers for unnumbered component links, including the
   case where a link is formed by a Forwarding Adjacency, follows the
   same rules as for an unnumbered TE link (see Section "Link
   Identifiers" of [RSVP-UNNUM]/[CRLDP-UNNUM]). Furthermore, link local
   identifiers for all unnumbered links of a given LSR (whether
   component links, Forwarding Adjacencies or bundled links) MUST be
   unique in the context of that LSR.

   The "liveness" of the bundled link is determined by the liveness of
   each of the component links within the bundled link - a bundled link
   is alive when at least one its component links is determined to be
   alive. The liveness of a component link can be determined by any of
   several means: IS-IS or OSPF hellos over the component link, or RSVP
   Hello, or LMP hellos (see [LMP]), or from layer 1 or layer 2
   indications.

   Once a bundled link is determined to be alive, it can be advertised
   as a TE link and the TE information can be flooded. If IS-IS/OSPF
   hellos are run over the component links, IS-IS/OSPF flooding can be
   restricted to just one of the component links. Procedures for doing



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   this are outside the scope of this document.

   In the future, as new Traffic Engineering parameters are added to IS-
   IS and OSPF, they should be accompanied by descriptions as to how
   they can be bundled, and possible restrictions on bundling.


4.3. Signaling Considerations

   Typically, an LSP's ERO will choose the bundled link to be used for
   the LSP, but not the component link, since information about the
   bundled link is flooded, but information about the component links is
   not. If the ERO chooses the component link by means outside the scope
   of this document, this section does not apply.  Otherwise, the choice
   of the component link for the LSP is a local matter between the two
   LSRs at each end of the bundled link.

   Signaling must identify both the component link to use and the label
   to use. The choice of the component link to use is always made by the
   sender of the Path/REQUEST message (if an LSP is bidirectional
   [GMPLS-SIG], the sender chooses a component link in each direction).
   For unidirectional LSPs, and the forward direction of bidirectional
   LSPs, the sender of a Resv/MAPPING message chooses the label. For the
   reverse direction of a bidirectional LSP, the sender of the
   Path/REQUEST message selects the upstream label.

   With RSVP the choice of the component link is indicated by the sender
   of the Path message by including the IF_ID RSVP_HOP object in the
   Path message, as described in section 8 of [GMPLS-RSVP].  With CR-LDP
   the choice of the component link is indicated by the sender of the
   REQUEST message by including the IF_ID TLV in the REQUEST message, as
   described in section 8 of [GMPLS-CRLDP].

   If the component link is numbered, the IF_ID RSVP_HOP object, or
   IF_ID TLV carries either Type 1 (IPv4 address) or Type 2 (IPv6
   address) TLVs (see [GMPLS-SIG]). The address carried in the TLV
   identifies the link for which label allocation must be done.

   If the component link is unnumbered, the IF_ID RSVP_HOP object, or
   IF_ID TLV carries Type 3 (IF_INDEX) TLV (see [GMPLS-SIG]). The value
   carried in Type 3 TLV contains the identifier of the selected
   component link assigned to the link by the sender of the Path/REQUEST
   message. Processing this object is the same as specified in Section
   "Processing the IF_ID RSVP_HOP object"/"Processing the IF_ID TLV" of
   [RSVP-UNNUM]/[CRLDP-UNNUM].

   For the purpose of processing the IF_ID RSVP_HOP object or IF_ID TLV,
   an unnumbered component link formed by a Forwarding Adjacency is



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   treated the same way as an unnumbered TE link formed by a Forwarding
   Adjacency (see Section "Unnumbered Forwarding Adjacencies" of [RSVP-
   UNNUM]/[CDLDP-UNNUM]).


5. Traffic Engineering Parameters for Bundled Links

   In this section, we define the Traffic Engineering parameters to be
   advertised for a bundled link, based on the configuration of the
   component links and of the bundled link. The definition of these
   parameters for component links was undertaken in [ISIS-TE] and [OSPF-
   TE]; we use the terminology from [OSPF-TE].


5.1. OSPF Link Type

   The Link Type of a bundled link is the (unique) Link Type of the
   component links. (Note: this parameter is not present in IS-IS.)


5.2. OSPF Link ID

   For point-to-point links, the Link ID of a bundled link is the
   (unique) Router ID of the neighbor. For multi-access links, this is
   the interface address of the (unique) Designated Router. (Note: this
   parameter is not present in IS-IS.)


5.3. Local and Remote Interface IP Address

   (Note: in IS-IS, these are known as IPv4 Interface Address and IPv4
   Neighbor Address, respectively.)

   If the bundled link is numbered, the Local Interface IP Address is
   the local address of the bundled link; similarly, the Remote
   Interface IP Address is the remote address of the bundled link.


5.4. Local and Remote Identifiers

   If the bundled link is unnumbered, the link local identifier is set
   to the identifier chosen for the bundle by the advertising LSR.  The
   link remote identifier is set to the identifier chosen by the
   neighboring LSR for the reverse link corresponding to this bundle, if
   known; otherwise, this is set to 0.






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5.5. Traffic Engineering Metric

   The Traffic Engineering Metric for a bundled link is that of the
   component links.


5.6. Maximum Bandwidth

   This parameter is not used. The maximum LSP Bandwidth (as described
   below) replaces the Maximum Bandwidth for bundled links.


5.7. Maximum Reservable Bandwidth

   We assume that for a given bundled link either each of its component
   links is configured with the Maximum Reservable Bandwidth, or the
   bundled link is configured with the Maximum Reservable Bandwidth. In
   the former case, the Maximum Reservable Bandwidth of the bundled link
   is set to the sum of the Maximum Reservable Bandwidths of all
   component links associated with the bundled link.


5.8. Unreserved Bandwidth

   The unreserved bandwidth of a bundled link at priority p is the sum
   of the unreserved bandwidths at priority p of all the component links
   associated with the bundled link.


5.9. Resource Classes (Administrative Groups)

   The Resource Classes for a bundled link are the same as those of the
   component links.


5.10. Maximum LSP Bandwidth

   The Maximum LSP Bandwidth takes the place of the Maximum Bandwidth.
   For an unbundled link the Maximum Bandwidth is defined in [GMPLS-
   ROUTING]. The Maximum LSP Bandwidth of a bundled link at priority p
   is defined to be the maximum of the Maximum LSP Bandwidth at priority
   p of all of its component links.

   The details of how Maximum LSP Bandwidth is carried in IS-IS is given
   in [GMPLS-ISIS]. The details of how Maximum LSP Bandwidth is carried
   in OSPF is given in [GMPLS-OSPF].





Kompella, K., Rekhter, Y., Berger, L.                           

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6. Bandwidth Accounting

   The RSVP (or CR-LDP) Traffic Control module, or its equivalent, on an
   LSR with bundled links must apply admission control on a per-
   component link basis. An LSP with a bandwidth requirement b and setup
   priority p fits in a bundled link if at least one component link has
   maximum LSP bandwidth >= b at priority p. If there are several such
   links, the choice of which link is used for the LSP is up to the
   implementation.

   In order to know the maximum LSP bandwidth (per priority) of each
   component link, the Traffic Control module must track the unreserved
   bandwidth (per priority) for each component link.

   A change in the unreserved bandwidth of a component link results in a
   change in the unreserved bandwidth of the bundled link. It also
   potentially results in a change in the maximum LSP bandwidth of the
   bundle; thus, the maximum LSP bandwidth should be recomputed.

   If one of the component links goes down, the associated bundled link
   remains up and continues to be advertised, provided that at least one
   component link associated with the bundled link is up.  The
   unreserved bandwidth of the component link that is down is set to
   zero, and the unreserved bandwidth and maximum LSP bandwidth of the
   bundle must be recomputed. If all the component links associated with
   a given bundled link are down, the bundled link MUST not be
   advertised into OSPF/IS-IS.


7. Security Considerations

   This document defines ways of utilizing procedures defined in other
   documents referenced herein.  Any security issues related to those
   procedures are addressed in the referenced drafts.  This document
   thus raises no new security issues for RSVP-TE [RSVP-TE] or CR-LDP
   [CR-LDP].















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8. References


8.1. Normative References

   [GMPLS-ISIS] Kompella, K., Rekhter, Y., Banerjee, A. et al, "IS-IS
   Extensions in Support of Generalized MPLS", draft-ietf-isis-gmpls-
   extensions-11.txt (work in progress)

   [GMPLS-OSPF] Kompella, K., Rekhter, Y., Banerjee, A. et al, "OSPF
   Extensions in Support of Generalized MPLS", draft-ietf-ccamp-ospf-
   gmpls-extensions-08.txt (work in progress)

   [GMPLS-ROUTING] Kompella, K., Rekhter, Y., Banerjee, A. et al,
   "Routing Extensions in Support of Generalized MPLS", draft-ietf-
   ccamp-gmpls-routing-04.txt (work in progress)

   [GMPLS-SIG] Ashwood, P., et al., "Generalized MPLS - Signalling
   Functional Description", draft-ietf-generalized-mpls-
   signalling-08.txt

   [GMPLS-RSVP] Ashwood, P., et al., "Generalized MPLS Signalling RSVP-
   TE Extensions", draft-ietf-mpls-generalized-rsvp-te-07.txt

   [GMPLS-CRLDP] Ashwood, P., et al., "Generalized MPLS Signaling - CR-
   LDP Extensions", draft-ietf-mpls-generalized-cr-ldp-06.txt

   [ISIS-TE] Smit, H., Li, T., "IS-IS extensions for Traffic
   Engineering", draft-ietf-isis-traffic-02.txt (work in progress)

   [OSPF-TE] Katz, D., Yeung, D., "Traffic Engineering Extensions to
   OSPF", draft-katz-yeung-ospf-traffic-04.txt (work in progress)

   [UNNUM-CRLDP] Kompella, K., Rekhter, Y., Kullberg, A., "Signalling
   Unnumbered Links in CR-LDP", draft-ietf-mpls-crldp-unnum-01.txt (work
   in progress)

   [UNNUM-RSVP] Kompella, K., Rekhter, Y., "Signalling Unnumbered Links
   in RSVP-TE", draft-ietf-mpls-rsvp-unnum-01.txt (work in progress)

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

   [RSVP-TE] Awduche, D., Berger, L., Gan, D. H., Li, T., Srinivasan,
   V., and Swallow, G., "RSVP-TE: Extensions to RSVP for LSP Tunnels",
   RFC3209, December 2001

   [CR-LDP] Jamoussi, B., editor, "Constraint-Based LSP Setup using



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   LDP", RFC3212, December 2001


8.2. Non-normative References

   [LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)",
   draft-ietf-ccamp-lmp-03.txt (work in progress)


9. Author Information


   Kireeti Kompella
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   Email: kireeti@juniper.net

   Yakov Rekhter
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089
   Email: yakov@juniper.net

   Lou Berger
   Movaz Networks, Inc.
   Voice: +1 301 468 9228
   Email: lberger@movaz.com























Kompella, K., Rekhter, Y., Berger, L.                           

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