Network Working Group Kireeti Kompella
Internet Draft Juniper Networks
Expiration Date: November 2002 Yakov Rekhter
Juniper Networks
Lou Berger
Movaz Networks
Link Bundling in MPLS Traffic Engineering
draft-ietf-mpls-bundle-03.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.
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2. Abstract
For the purpose of GMPLS signaling in certain cases a combination of
<link identifier, label> is not sufficient to unambiguously identify
the appropriate resource used by an LSP. Such cases are handled by
using the link bundling construct which is described in this
document.
Kompella, K., Rekhter, Y., Berger, L. [Page 1]
Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
3. 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
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.
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Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
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 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 4 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
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.
Kompella, K., Rekhter, Y., Berger, L. [Page 3]
Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
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, 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
6.1 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
treated the same way as an unnumbered TE link formed by a Forwarding
Adjacency (see Section 5 of [RSVP-UNNUM]/[CDLDP-UNNUM]).
Kompella, K., Rekhter, Y., Berger, L. [Page 4]
Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
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-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. 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.
4.5. Traffic Engineering Metric
The Traffic Engineering Metric for a bundled link is that of the
component links.
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Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
4.6. Maximum Bandwidth
This parameter is not used. The maximum LSP Bandwidth (as described
below) replaces the Maximum Bandwidth for bundled links.
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
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 Bandwidth.
For an unbundled link the Maximum Bandwidth is 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].
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Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
5. 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.
6. Security Considerations
This document raises no new security issues for RSVP-TE or CR-LDP.
7. References
7.1. 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,
Kompella, K., Rekhter, Y., Berger, L. [Page 7]
Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
"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)
7.2. Non-normative References
[LMP] Lang, J., Mitra, K., et al., "Link Management Protocol (LMP)",
draft-ietf-ccamp-lmp-03.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
Kompella, K., Rekhter, Y., Berger, L. [Page 8]
Internet Draft draft-ietf-mpls-bundle-03.txt May 2002
Lou Berger
Movaz Networks, Inc.
Voice: +1 301 468 9228
Email: lberger@movaz.com
Kompella, K., Rekhter, Y., Berger, L. [Page 9]
