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Network Working Group                              Kireeti Kompella
Internet Draft                                     Juniper Networks
Expiration Date: January 2001                         Yakov Rekhter
                                                      Cisco Systems
                                                         Lou Berger
                                               LabN Consulting, LLC

               Link Bundling in MPLS Traffic Engineering

                   draft-kompella-mpls-bundle-02.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 how to accomplish this.










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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 interfaces 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".


3.1. Restrictions on Bundling

   All component links in a bundle must have the same Link Type (if
   any), the same Traffic Engineering metric, the same set of resource
   classes, and the same Link Multiplex Capability (see [RTG]).

   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.

   Component links may be unnumbered, or the various component links may
   be numbered differently, or all components links may be numbered
   identically.  In the first two cases, the bundled link is unnumbered
   by default; in the last case, the bundled link is numbered the same
   as the component links by default.  In all cases, the bundled link's
   addresses may be overridden by configuration with IP addresses
   assigned to some "virtual" interfaces on an LSR (it is assumed that
   an LSR may have multiple virtual interfaces).


3.2. Other Considerations

   If several component links are bundled, IS-IS/OSPF flooding can be
   restricted to just one of the component links.  Similarly, IS-IS/OSPF
   hellos can be restricted to just one component link; however, it may
   be useful to send hellos on all links that do not have a link layer
   keep-alive mechanism to ensure that a failure of the link is
   detected.

   If the component links are not Packet Switch Capable, LSP setup
   signalling needs to identify the component link to use.  This
   protocol is outside the scope of this document; however, see [LMP].

   If a bundled link consists of "working" and "protect" component
   links, then for the purposes of bandwidth computation, only the



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   working links should be taken into account.

   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. 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. 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. 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 (see section 3.1), 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.

   If the bundled link is unnumbered, the Local Address is the Router ID
   of the advertising LSR, and the Remote Address is the Router ID of
   the neighboring LSR.








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4.4. Traffic Engineering Metric

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


4.5. 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.


4.6. 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.


4.7. 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.


4.8. Resource Classes (Administrative Groups)

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


4.9. 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.




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   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.

   In IS-IS, the Maximum LSP Bandwidth TLV is a sub-TLV of the Extended
   IS Reachability TLV with type 21.  In OSPF, this TLV is a sub-TLV of
   the Link TLV within the Traffic Engineering LSA, with type 11.  The
   length of the Maximum LSP Bandwidth TLV is 32 octets.  The value is a
   list of eight 4 octet fields in IEEE floating point format of the
   Maximum LSP Bandwidth of the bundle, from priority 0 to priority 7.


5. Procedures


5.1. Bandwidth Accounting

   The RSVP Traffic Control module 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 RSVP 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



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   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 message identifies the component link
   to be used for the LSP.  The sender of the Resv message chooses the
   label (as before).  If the bundled link is composed of packet-switch
   capable links and there is no designated control channel, then the
   component link to be used is the link over which the Path message is
   sent.

   If, however, there is a protocol such as LMP that uniquely identifies
   each component link and allocates a designated control channel, then
   the sender of the Path message MUST send the Path message over the
   control channel.  In this case, the LINK_ID object is used to
   identify the component link to use.  This method of choosing the link
   is required if the component links are not packet-switch capable.


5.2.1. LINK_ID object

   A new object, the LINK_ID object, is defined.  The Length field is
   set to 8.  The Class Num and C_Type of the LINK_ID object are to be
   obtained from IANA.  The format is given below; it consists simply of
   a 32-bit Link Identifier that identifies the link to be used for the
   LSP being set up.

       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 (TBD) |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Link Identifier                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This object is an optional subobject of the Path and Resv messages.

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

   If the receiver doesn't recognize the LINK_ID object, it SHOULD send
   an error message with an "Unknown Object Class" or an "Unknown Object
   C-Type" error.  A node that recognizes the LINK_ID object, but that



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   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 Link Identifier in the LINK_ID object,
   the receiver SHOULD send an error message with the error code
   "Routing problem" and the error value "Unknown Link ID".


6. Security Considerations

   This document raises no new security issues for IS-IS, OSPF or RSVP.


7. References

   [ISIS] Smit, H., Li, T., "IS-IS extensions for Traffic Engineering",
   draft-ietf-isis-traffic-01.txt (work in progress)

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

   [OSPF] Katz, D., Yeung, D., "Traffic Engineering Extensions to OSPF",
   draft-katz-yeung-ospf-traffic-01.txt (work in progress)

   [RSVP-TE] Awduche, D., Berger, L., Gan, D., et al, "Extensions to
   RSVP for LSP Tunnels", draft-ietf-mpls-rsvp-lsp-tunnel-05.txt (work
   in progress)

   [RTG] Kompella, K., Rekhter, Y., et al, "Extensions to IS-IS/OSPF and
   RSVP in support of MPL(ambda)S", draft-kompella-mpls-optical.txt
   (work in progress) (new version forthcoming)


8. Author Information


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

   Yakov Rekhter
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134
   Email: yakov@cisco.com



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   Lou Berger
   LabN Consulting, LLC
   Voice: +1 301 468 9228
   Email: lberger@labn.net















































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