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Network Working Group                                   Kireeti Kompella
Internet Draft                                          Juniper Networks
Expiration Date: August 2001                               Yakov Rekhter
                                                        Juniper Networks
                                                              Lou Berger
                                                          Movaz Networks

               Link Bundling in MPLS Traffic Engineering

                   draft-kompella-mpls-bundle-05.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

   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.  This document also defines corresponding signaling (RSVP-TE
   and CR-LDP) support.








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3. 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".

   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, the same set of
   resource classes, and the same Link Multiplex Capability (see [LSP-
   HIER]).  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-ISIS] and [GMPLS-OSPF]).  The "liveness" of the bundled
   link is determined by the liveness of each of the component links
   within the bundled link.  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



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   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 LSR (e.g., when the TE link is an
   FA).

   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
   kept local to the LSR.  If the ERO chooses the component links by
   means outside the scope of this document, neither this section nor
   section 5.2 applies.  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.

   The choice of the component link to use is always made by the sender
   of the Path/REQUEST message.  Three mechanisms for indicating this
   choice to the receiver of the Path/REQUEST message are discussed
   below; which of these mechanisms is used SHOULD be configurable by
   the user, preferably on a per-bundle basis.


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 IP Address

   This mechanism requires that each component link has a unique remote
   IP address.  The sender can either send the Path/REQUEST message
   addressed to the remote IP address for the component link or
   encapsulate the message in an IP header whose destination address is



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   the remote IP address.  This mechanism does not require each
   component link to have its own control channel.  In fact, it doesn't
   even require the whole (bundled) link to have its own control
   channel.


3.3.3. Mechanism 3: Explicit Indication by Component Interface ID

   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.  This identifier is referred to as "component interface
   identifier".  The choice of the component link is indicated by the
   sender of the Path/REQUEST message by including the component link's
   interface identifier in the message, as described in section 5.2.


3.4. Unnumbered Bundled Links

   Note that 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.


4. 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] and [OSPF];
   we use the terminology from [OSPF].


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.)










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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.


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.  For backward
   compatibility, one MAY advertise the Maximum LSP Bandwidth at
   priority 7 of the bundle as the Maximum Link Bandwidth.


4.7. 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



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   is set to the sum of the maximum 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.  However, while Maximum Link Bandwidth is a single fixed
   value (usually simply the link capacity), Maximum LSP Bandwidth is
   carried per priority, and may vary as LSPs are set up and torn down.

   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 each
   component link.

   If a component link is a simple (unbundled) link, define its Maximum
   LSP Bandwidth at priority p to be the smaller of its unreserved
   bandwidth at priority p and its maximum link bandwidth.

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

   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].











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5. Procedures


5.1. 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.  This is done as
   follows.  If an LSP with bandwidth b and holding priority p is set up
   through a component link, that component link's unreserved bandwidth
   at priority p and lower is reduced by b.  If an LSP with bandwidth b
   and holding priority p that is currently set up through a component
   link is torn down, the unreserved bandwidth at priority p and lower
   for that component link is increased by b.

   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.


5.2. Signaling

   Signaling must identify both the component link to use and the label
   to use.  The sender of the Path/REQUEST message always chooses the
   component link(s) to be used for the LSP (if the LSP is bidirectional
   [GMPLS-SIG], the sender chooses a component link in each direction).

   For unidirectional LSPs and the forward direction of a bidirectional
   LSP, the sender of a MAPPING/Resv message chooses the label (if
   needed).  For the reverse direction of a bidirectional LSP, the



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   sender of the Path/REQUEST message selects the upstream label (if
   needed).

   As mentioned above, there are three methods for communicating the
   selected component link, implicit indication and explicit indication
   by IP address and by component interface identifier.  The first two
   are described in sections 3.3.1 and 3.3.2.  In this section, we
   define the objects needed to indicate the component link by component
   interface identifier.

   In explicit indication by component interface identifier, the sender
   of the Path (REQUEST) message communicates the selected component
   link via the COMPONENT_INTERFACE_ID object class (Component Interface
   ID TLV) defined below.  Doing this assumes that an LSR connected to a
   component link knows the component interface identifier assigned to
   that link by the LSR at the other end of the link.  Exchanging the
   identity of a component link between the LSRs connected by that link
   may be accomplished by configuration, by means of a protocol such as
   [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.

   In both RSVP and CR-LDP, if a Component Interface Identifier has the
   special value of 0xFFFFFFFF, this means that the same label is to be
   valid across all component links.


5.2.1. RSVP-TE COMPONENT_INTERFACE_ID Object Class

   A new object class, the COMPONENT_INTERFACE_ID object class, is
   defined.  The Length field is set to 8.  The Class Num (TBD) is of
   the form 0bbbbbbb.  The DOWNSTREAM_COMPONENT_INTERFACE_ID object,
   which has a C_Type of 1, is used to indicate the component interface
   to be used for traffic flowing in the downstream direction.  The
   UPSTREAM_COMPONENT_INTERFACE_ID object, which has a C_Type of 2, is
   used to indicate the component interface to be used for traffic
   flowing in the upstream direction.  Both objects have the same format
   and carry a 32-bit Component Interface Identifier.  The format of the
   objects are:

       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 (TBD)|  C_Type (1|2) |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Component Interface Identifier                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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5.2.2. COMPONENT_INTERFACE_ID Object Class Usage

   The COMPONENT_INTERFACE_ID objects are carried in RSVP messages as
   part of the sender descriptor.  They are optional with respect to the
   protocol, and are only used when component links are being identified
   using the COMPONENT_INTERFACE_ID objects.  There are two formats for
   the sender descriptor, one for traditional LSPs and one for
   bidirectional LSPs.

   The format of the sender descriptor for unidirectional LSPs is:

          <sender descriptor> ::=  <SENDER_TEMPLATE> <SENDER_TSPEC>
                                   [ <ADSPEC> ]
                                   [ <RECORD_ROUTE> ]
                                   <DOWNSTREAM_COMPONENT_INTERFACE_ID>
                                   [ <SUGGESTED_LABEL> ]

   The format of the sender descriptor for bidirectional LSPs is:

          <sender descriptor> ::=  <SENDER_TEMPLATE> <SENDER_TSPEC>
                                   [ <ADSPEC> ]
                                   [ <RECORD_ROUTE> ]
                                   <DOWNSTREAM_COMPONENT_INTERFACE_ID>
                                   [ <SUGGESTED_LABEL> ]
                                   <UPSTREAM_COMPONENT_INTERFACE_ID>
                                   <UPSTREAM_LABEL>

   We introduce a new error value for the error code "Routing problem",
   namely "Unknown Component Interface ID" with error value 11.

   If the receiver doesn't recognize the COMPONENT_INTERFACE_ID object
   class, per [RSVP], it SHOULD send an error message with an "Unknown
   Object Class". If the class is recognized but the C-Type is not, per
   [RSVP], the receiver SHOULD send an "Unknown Object C-Type" error.  A
   node that recognizes either COMPONENT_INTERFACE_ID objects, but that
   is unable to support it (possibly because of a failure to allocate
   labels) SHOULD send an error message with the error code "Routing
   problem" and the error value "MPLS label allocation failure."  If LMP
   or some other link identification protocol is not running, or there
   is no component link with the Component Interface Identifier in
   either object, the receiver SHOULD send an error message with the
   error code "Routing problem" and the error value "Unknown Component
   Interface ID".








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5.2.3. CR-LDP Component Interface ID TLVs

   Two new TLVs are introduced to support bundling in CR-LDP.  Both TLVs
   are carried in LDP REQUEST messages.  The TLVs share a common format
   and differ in the direction of the component link being identified.
   The Downstream Component Interface ID TLV, which has a Type value to
   be determined by IETF consensus, is used to indicate the component
   interface to be used for traffic flowing in the downstream direction.
   The Upstream Component Interface ID TLV, which has a Type value to be
   determined by IETF consensus, is used to indicate the component
   interface to be used for traffic flowing in the upstream direction.
   Both TLVs have the same format and carry a 32-bit Component Interface
   Identifier.  The format of the TLVs are:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |U|F|   Type = (TBD | TBD)      |             Length (8)        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Component Interface Identifier                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   We introduce a new status code "Unknown Component Interface ID" with
   value 0x1A.

   If the receiver doesn't recognize either Component Interface ID TLV
   class, per [LDP], it SHOULD send a Notification message with an "Unknown
   TLV" Status Code.  A node that recognizes either Component Interface ID
   TLV, but that is unable to support it (possibly because of a failure to
   allocate labels) SHOULD send a Notification message with a "No Label
   Resources" Status Code.  If LMP or some other link identification
   protocol is not running, or there is no component link with the
   Component Interface Identifier in either TLV, the receiver SHOULD send a
   Notification message with an "Unknown Component Interface ID" Status
   Code.
















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6. Security Considerations

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


7. 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-kompella-ospf-
   gmpls-extensions-01.txt (work in progress)

   [GMPLS-SIG] Ashwood, P., et al., "Generalized MPLS - Signalling
   Functional Description", draft-ietf-generalized-mpls-
   signalling-02.txt

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

   [LDP] Andersson, L. et al, "LDP Specification", RFC 3036, January
   2001.

   [LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)",
   draft-ietf-mpls-lmp-02.txt (work in progress)

   [LSP-HIER] Kompella, K., Rekhter, Y., "LSP Hierarchy with MPLS TE",
   draft-ietf-mpls-lsp-hierarchy-01.txt (work in progress)

   [MOY] Moy, J., draft-ietf-ospf-ppp-flood-00.txt (work in progress)

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

   [RSVP] Braden, Ed., et. al., "Resource ReSerVation Protocol (RSVP) --
   Version 1 Functional Specification", RFC2205, September 1997.

   [RSVP-TE] Awduche, D., Berger, L., Gan, D., et al, "Extensions to
   RSVP for LSP Tunnels", draft-ietf-mpls-rsvp-lsp-tunnel-08.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



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   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)


8. 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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