Network Working Group Kireeti KompellaInternet Draft Kireeti Kompella
Updates: 3471 Juniper Networks
Expiration Date: January 2003
Category: Standards Track Yakov Rekhter
Expiration Date: April 2005 Juniper Networks
Link Bundling in MPLS Traffic Engineering
1. Status of this Memo
This document is an Internet-Draft
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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.
This document updates the interface identification TLVs defined in
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 <TE link identifier, label>
is sufficient to unambiguously identify the appropriate resource used
by an LSP. In other cases, a combination of <link <TE 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 <TE 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".
Furthermore we restrict the identifiers that can be used to identify
component links such that they have node scope. On a bundled link a
combination of <(bundled) link identifier, component <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.
Both ends of the bundled link also have to understand each others
component link identifiers.
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.
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
Component link identifiers MUST have node wide scope and MUST be
unique across both TE and component link identifiers.
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]). [RFC3477]/[RFC3480]). 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
Once a bundled link is determined to be alive, it can
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
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 identify 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 The identification of a component link by means in an ERO is outside the
scope of this document, this section does not apply. Otherwise, document. When the bundled link is identified in an
ERO or is dynamically identified, the choice of the component link
for the LSP is a local matter between the two LSRs at each end of the
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
[RFC3471], the sender chooses a component link in each direction).
For unidirectional LSPs, and
The handling of labels is not modified by this document.
With RSVP the forward direction choice of bidirectional
LSPs, the component link is indicated by the sender
of a Resv/MAPPING the Path message chooses by including the label. For IF_ID RSVP_HOP object in the
Path message, as described in section 8 of [RFC3473]. With CR-LDP
the choice of a bidirectional LSP, the component link is indicated by the sender of the
REQUEST message selects by including the upstream label. IF_ID TLV in the REQUEST message, as
described in section 8 of [RFC3472].
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]. [RFC3473]. 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 [RFC3472]. Additional processing related
to unnumbered links is numbered, described in the "Processing the IF_ID
RSVP_HOP object, or object"/"Processing the IF_ID TLV carries either Type 1 (IPv4 address) or Type 2 (IPv6
address) TLV" and "Unnumbered
Forwarding Adjacencies" sections of [RFC3477]/[RFC3480].
[RFC3471] defines the Interface Identification TLV types. This
document specifies that the TLV types 1, 2 and 3 SHOULD be used to
indicate component links in IF_ID RSVP_HOP objects and IF_ID TLVs.
Type 1 TLVs (see [GMPLS-SIG]). are used for IPv4 numbered component link identifiers.
Type 2 TLVs are used for IPv6 numbered component links identifier.
Type 3 TLVs are used for unnumbered component link identifiers. The address carried
Component Interface TLVs, TLV types 4 and 5, SHOULD NOT be used.
Except in the special case noted below, for a unidirectional LSP,
only a single TLV
identifies SHOULD be used in an IF_ID RSVP_HOP object or IF_ID
TLV. This TLV indicates the component link for identifier of the
downstream data channel on which label allocation must be done.
If the component link is unnumbered,
Except in the special case noted below, for a bidirectional LSP, only
one or two TLVs SHOULD used in an IF_ID RSVP_HOP object, object or IF_ID TLV carries Type 3 (IF_INDEX) TLV (see [GMPLS-SIG]). TLV.
carried in Type 3 first TLV contains always indicates the component link identifier of the
downstream data channel on which label allocation must be done. When
present, the second TLV always indicates the component link
identifier of the selected upstream data channel on which label allocation
must be done. When only one TLV is present, it indicates the
component link assigned identifier for both downstream and upstream data
In the special case where the same label is to be valid across all
component links, two TLVs SHOULD used in an IF_ID RSVP_HOP object or
IF_ID TLV. The first TLV indicates the TE link identifier of the
bundle on which label allocation must be done. The second TLV
indicates a bundle scope label. For TLV types 1 and 2 this is done
by using the sender special bit value of the Path/REQUEST
message. Processing all ones (1), e.g., 0xFFFFFFFF for
a type 1 TLV. Per [RFC3471], for TLV types 3, 4 and 5, this object is done
by setting the same as specified in Section
"Processing Interface ID field to the special value 0xFFFFFFFF.
Note that this special case applies to both unidirectional and
Although SHOULD NOT be used, when used, the type 5 TLV MUST NOT be
the first TLV in an IF_ID RSVP_HOP object"/"Processing the object or IF_ID TLV" TLV.
4.3.1. Interface Identification TLV Format
This section modifies section 9.1.1. of [RFC3471]. The definition of
the IP Address field of
[RSVP-UNNUM]/[CRLDP-UNNUM]. the TLV types 3, 4 and 5 is clarified.
For types 3, 4 and 5 the purpose Value field has the identical format as
the contents of processing the IF_ID RSVP_HOP C-Type 1 LSP_TUNNEL_INTERFACE_ID object or IF_ID TLV,
an unnumbered component link formed by a Forwarding Adjacency is
defined in [RFC3477]. Note this results in the same way as an unnumbered TE link formed by a Forwarding
Adjacency (see Section "Unnumbered Forwarding Adjacencies" renaming of [RSVP-
UNNUM]/[CDLDP-UNNUM]). the IP
Address field defined in [RFC3471].
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] [RFC3784] and [OSPF-
[RFC3630]; we use the terminology from [OSPF-TE]. [RFC3630].
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.
5.5. Traffic Engineering Metric
The Traffic Engineering Metric for a bundled link is that of the
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. link
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].
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
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] [RFC3209] or CR-LDP
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- draft-ietf-ibis-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-12.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.,
[RFC3471] Berger, L., et al., "Generalized MPLS - Signalling Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", draft-ietf-generalized-mpls-
[GMPLS-RSVP] Ashwood, P., RFC 3471,
[RFC3473] Berger, L., et al., "Generalized MPLS Signalling RSVP-
TE Extensions", draft-ietf-mpls-generalized-rsvp-te-07.txt
[GMPLS-CRLDP] Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions.", RFC 3473, January 2003.
[RFC3472] Ashwood, P., Berger, L., et al., "Generalized MPLS Multi-
Protocol Label Switching (GMPLS) Signaling - CR-
LDP Extensions", draft-ietf-mpls-generalized-cr-ldp-06.txt
[ISIS-TE] Constraint-based Routed
Label Distribution Protocol (CR-LDP) Extensions.", RFC 3472,January
[RFC3784] Smit, H., Li, T., "IS-IS extensions "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic
Engineering", draft-ietf-isis-traffic-02.txt (work in progress)
[OSPF-TE] Engineering (TE)", RFC 3784,
[RFC3630] Katz, D., Kompella, K., Yeung, D., "Traffic Engineering
(TE) Extensions to
OSPF", draft-katz-yeung-ospf-traffic-04.txt (work in progress)
[UNNUM-CRLDP] OSPF Version 2", RFC 3630, September 2003.
[RFC3480] Kompella, K., Rekhter, Y., Kullberg, A., "Signalling
Unnumbered Links in CR-LDP", draft-ietf-mpls-crldp-unnum-01.txt (work RFC 3480, February 2003. in progress)
[RFC3477] Kompella, K., Rekhter, Y., "Signalling Unnumbered Links in
RSVP-TE", draft-ietf-mpls-rsvp-unnum-01.txt (work in progress) RFC 3477, January 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] 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
[RFC3212] Jamoussi, B., editor, "Constraint-Based LSP Setup using
LDP", RFC3212, December 2001
8.2. Non-normative References
[LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)",
draft-ietf-ccamp-lmp-10.txt (work in progress)
9. Author Information
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
Movaz Networks, Inc.
Voice: +1 301 468 9228 703-847-1801
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