Network Working Group                                   Kireeti Kompella
Internet Draft                                          Juniper Networks
Expiration Date: March 2002                                Yakov Rekhter
                                                        Juniper Networks
                                                              Lou Berger
                                                          Movaz Networks

               Link Bundling in MPLS Traffic Engineering

                     draft-ietf-mpls-bundle-00.txt


. 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
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   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.


. Abstract

   In some cases a pair of Label Switching Routers (LSRs) may be
   connected by several (parallel) links. From the MPLS Traffic
   Engineering point of view for reasons of scalability it may be
   desirable to advertise all these links as a single link into OSPF
   and/or IS-IS. This document describes a mechanism to accomplish this.











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. Link Bundling

   When a pair of LSRs are connected by multiple links, then for the
   purpose of MPLS Traffic Engineering it is possible to advertise
   several (or all) of these links as a single link into OSPF and/or IS-
   IS.  We refer to this process as "link bundling", or just "bundling".
   We refer to the link that is advertised into OSPF/IS-IS as a "bundled
   link". We refer to the links associated with that bundled link as
   "component links".

   Link bundling can be applied recursively. That is, a bundled link
   that consists of multiple component links may itself be a component
   link of some other 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
   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.


3.1. 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.


3.2. Routing Considerations

   A bundled link is just another kind of Traffic Engineering (TE) link
   (see [GMPLS-ROUTING]). 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



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   (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 [ZININ] [MOY].

   Note that advertising a (bundled) TE link between a pair of LSRs
   doesn't imply that there is an IGP adjacency between these LSRs that
   is associated with just that link. In fact, in certain cases a TE
   link between a pair of LSRs could be advertised even if there is no
   IGP adjacency at all between the LSRs (e.g., when the TE link is an
   FA).

   A component link may be either numbered or unnumbered. A bundled link
   may itself be numbered or unnumbered independent of whether the
   component links are numbered or not. This affects how the bundled
   link is advertised in IS-IS/OSPF, and the format of LSP EROs that
   traverse the bundled link. Furthermore, unnumbered Interface
   Identifiers for all unnumbered outgoing links of a given LSR (whether
   component links, Forwarding Adjacencies or bundled links) MUST be
   unique in the context of that LSR.

   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.


3.3. Signaling Considerations

   Typically, an LSP's ERO will choose the bundled link to be used for
   the LSP, but not the component link(s), since information about the
   bundled link is flooded, but information about the component links is
   not. If the ERO chooses the component links by means outside the
   scope of this document, this section does not apply.  Otherwise, the
   choice of the component link(s) 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.

   Two mechanisms for identifying the component link to the receiver of



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   the Path/REQUEST message are described below; which of these
   mechanisms is used SHOULD be configurable by the user, preferably on
   a per-bundle basis. Both mechanisms work with either numbered or
   unnumbered component links.


3.3.1. Mechanism 1: Implicit Indication

   This mechanism requires that each component link has a dedicated
   signaling channel (for example, the link is packet-switch capable; or
   the link is a SONET link with an in-band channel for signaling). The
   sender of the Path/REQUEST message tells the receiver which component
   link to use by sending the message over the chosen component link's
   dedicated signaling channel.



3.3.2. Mechanism 2: Explicit Indication by Interface ID

   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]). If the component link is unnumbered,
   the IF_ID RSVP_HOP object, or IF_ID TLV carries Type 4
   (COMPONENT_IF_DOWNSTREAM) TLV, and in the case of a bidirectional LSP
   also Type 5 (COMPONENT_IF_UPSTREAM) TLV (see [GMPLS-SIG]).  The value
   carried in Type 4 and Type 5 TLVs contains the outgoing interface
   identifier (from the point of view of the sender of the Path/REQUEST
   message) of the selected component link.

   When the IF_ID RSVP_HOP or IF_ID TLV carries the IPv4 or IPv6 address
   (component link is numbered), this address identifies the link for
   which label allocation must be done.

   When a component link is unnumbered, this mechanism requires that
   each component link is assigned a unique Interface Identifier per
   [UNNUM-RSVP] or [UNNUM-CRLDP], and that the assigned identifiers be
   exchanged by the two LSRs at each end of the bundled link.
   Exchanging the identifiers may be accomplished by configuration, by
   means of a protocol such as LMP ([LMP]), by means of RSVP/CR-LDP
   (especially in the case where a component link is a Forwarding
   Adjacency), or by means of IS-IS or OSPF extensions ([ISIS-GMPLS],



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   [OSPF-GMPLS]).

   When the IF_ID RSVP_HOP or IF_ID TLV carries the
   COMPONENT_IF_DOWNSTREAM TLV (component link is unnumbered), the LSR
   that receives the Path/REQUEST message determines the component link
   for which label allocation must be done as follows. First the LSR
   checks whether the tuple <IP Address, Interface ID> carried in
   COMPONENT_IF_DOWNSTREAM matches the tuple <Router ID, Forwarding
   Interface ID> (see [RSVP-UNNUM], [CRLDP-UNNUM]) of any LSPs for which
   the LSR is a tail-end. If the match is found, the match identifies
   the Forwarding Adjacency for which the LSR has to perform label
   allocation.

   Otherwise, the LSR must check whether the tuple <IP Address,
   Interface ID> carried in COMPONENT_IF_DOWNSTREAM matches the tuple
   <Router ID, Reverse Interface ID> (see [RSVP-UNNUM], [CRLDP-UNNUM])
   of any of the bidirectional LSPs for which the LSR is the head-end.
   If a match is found, the match identifies the Forwarding Adjacency
   for which the LSR has to perform label allocation, namely, the
   reverse Forwarding Adjacency for the LSP identified by the match.

   Otherwise, the LSR must have information about the identifiers
   assigned by its neighbors to the component links (i.e., incoming
   interface identifiers from LSR's point of view). The LSR uses this
   information to find a (component) link with tuple <Router ID,
   incoming interface identifier> matching the tuple <IP Address,
   Interface ID> carried in COMPONENT_IF_DOWNSTREAM. If the matching
   tuple is found, the match identifies the (component) link for which
   the LSR has to perform label allocation.

   In both RSVP and CR-LDP, if the Interface ID field of
   COMPONENT_IF_DOWNSTREAM has the special value of 0xffffffff, this
   means that the same label is to be valid across all component links
   in the downstream direction. Likewise, if the Interface ID field of
   COMPONENT_IF_UPSTREAM has the special value of 0xffffffff, this means
   that the same label is to be valid across all component links in the
   upstream direction.














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. 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].


4.1. 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.)


4.2. 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.)


4.3. 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.


4.4. Outgoing and Incoming Interface Identifiers

   If the bundled link is unnumbered, the Outgoing Interface Identifier
   is set to the outgoing interface identifier chosen for the bundle by
   the advertising LSR. The Incoming Interface Identifier is set to the
   outgoing interface 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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4.5. Traffic Engineering Metric

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


4.6. Maximum Link Bandwidth

   This TLV is not used. The maximum LSP Bandwidth (as described below)
   replaces the maximum link bandwidth for bundled links.


4.7. Total Reservable Bandwidth

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


4.8. 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.


4.9. Resource Classes (Administrative Groups)

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


4.10. Maximum LSP Bandwidth

   The Maximum LSP Bandwidth takes the place of the Maximum Link
   Bandwidth. It is defined in [GMPLS-ROUTING]. The details of how
   Maximum LPS 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].

   Maximum LSP Bandwidth of a bundled link is equal to the maximum of
   Maximum LSP Bandwidth of all of its component links.

   Since bundling may be applied recursively, a component link may
   itself be a bundled link. In this case, its Maximum LSP Bandwidth as



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   a component link is the same as its Maximum LSP Bandwidth as a
   bundled link.


. 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.



. Security Considerations

   This document raises no new security issues for RSVP or CR-LDP.














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. References

   [GMPLS-ISIS] Kompella, K., Rekhter, Y., Banerjee, A. et al, "IS-IS
   Extensions in Support of Generalized MPLS", draft-ietf-isis-gmpls-
   extensions-02.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-00.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-00.txt

   [GMPLS-SIG] Ashwood, P., et al., "Generalized MPLS - Signalling
   Functional Description", draft-ietf-generalized-mpls-
   signalling-05.txt

   [GMPLS-RSVP] Ashwood, P., et al., "Generalized MPLS Signalling RSVP-
   TE Extensions", draft-ietf-mpls-generalized-rsvp-te-04.txt

   [GMPLS-CRLDP] Ashwood, P., et al., "Generalized MPLS Signaling - CR-
   LDP Extensions", draft-ietf-mpls-generalized-cr-ldp-04.txt

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

   [LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)",
   draft-ietf-ccamp-lmp-00.txt (work in progress)

   [MOY] Moy, J., draft-ietf-ospf-ppp-flood-00.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)

   [ZININ] Zinin, A., Shand, M., "Flooding optimizations in link-state
   routing protocols", draft-ietf-ospf-isis-flood-opt-00.txt (work in
   progress)






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. 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
































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