Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems, Inc
Expires: December 22, 2006 Matthew. R. Meyer
Global Crossing
K. Kumaki
KDDI Corporation
Alberto. Tempia Bonda
Telecom Italia
June 20, 2006
A Link-Type sub-TLV to convey the number of Traffic Engineering Label
Switch Paths signalled across a link
draft-ietf-mpls-number-0-bw-te-lsps-02
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Abstract
Several Link-type sub-TLVs have been defined for OSPF and ISIS in the
context of MPLS Traffic Engineering in order to advertise some link
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characteristics such as the available bandwidth, traffic engineering
metric, administrative group and so on. There are various
circumstances (for example in order to load balance unconstrained TE
Label Switched Path (LSP) across a set of equal cost paths) where it
would be useful to also advertise the number of unconstrained Traffic
Engineering Label Switched Path(s) (TE LSP) signalled across a link.
This document specifies a new Link-type Traffic Engineering sub-TLV
used to advertise the number of unconstrained TE LSP(s) signalled
across a link.
Requirements Language
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].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol extensions . . . . . . . . . . . . . . . . . . . . . . 4
3.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Elements of procedure . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
A set of Link-type sub-TLVs have been defined for OSPF and ISIS (see
[I-D.ietf-isis-te-bis] and [RFC3630]) in the context of MPLS Traffic
Engineering in order to advertise various link characteristics such
as the available bandwidth, traffic engineering metric,
administrative group and so on. There are various circumstances
(detailed below) where it would be useful to also advertise the
number of unconstrained Traffic Engineering Label Switch Path(s) (TE
LSP).
It is not uncommon to deploy MPLS Traffic Engineering for the sake of
fast recovery relying on a local protection recovery mechanism such
as MPLS TE Fast Reroute (see [RFC4090]). In this case, a deployment
model consists of deploying a full mesh of unconstrained TE LSPs
between a set of LSRs and protect these TE LSPs with pre-established
backup tunnels against link, SRLG and/or node failures. The traffic
routed onto such unconstrained TE LSP simply follows the IGP shortest
path but is protected with MPLS TE Fast Reroute.
With MPLS Traffic Engineering a usual rerouting criteria is the
discovery of a better path for a TE LSP where a better path is
defined as a path with a lower cost according to a specific metric;
other metric such that the percentage of reserved bandwidth or the
number of hops can also be used. Unfortunately, for instance in the
presence of ECMPs (Equal Cost Multi-Paths) in symmetrical networks
when unconstrained TE LSP are used, such metrics are usually
ineffective and may lead to poorly load balanced traffic. If the
number of unconstrained TE LSPs traversing each link in the network
is known, various algorithms can be designed so as to efficiently
load balance the traffic carried onto such unconstrained TE LSPs. As
currently defined in [RFC3630] and [I-D.ietf-isis-te-bis] the
information related to the number of unconstrained TE LSP(s) is not
available. This document specifies a new Link-type Traffic
Engineering sub-TLV used to indicate the number of unconstrained TE
LSP signalled across a link.
Note that the specification of load balancing algorithms is outside
of the scope of this document and merely listed for the sake of
illustration of the motivation for gathering such information.
Furthermore, the knowledge of the number of unconstrained TE LSPs
signalled across each link can be used for other purposes (e.g.
management, ...).
2. Terminology
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Terminology used in this document
LSA: Link State Advertisement.
LSP: Link State Packet.
LSR: Label Switching Router.
TE LSP: Traffic Engineering Label Switched Path.
Unconstrained TE LSP: A TE LSP signalled with a bandwidth equal to 0.
3. Protocol extensions
A new Sub-TLV named NB-O-BW-LSP is defined that specifies the number
of unconstrained TE LSPs signalled across a link.
3.1. IS-IS
The NB-0-BW-LSP sub-TLV is OPTIONAL and MUST appear at most once
within the extended IS reachability TLV (type 22) specified in
[I-D.ietf-isis-te-bis].
The IS-IS NB-0-BW-LSP sub-TLV format is defined below:
Type (1 octet): To be assigned by IANA (suggested value = 19)
Length (1 octet): 4
Value (4 octets): number of unconstrained TE LSP(s) signalled across
the link.
3.2. OSPF
The NB-0-BW-LSP sub-TLV is OPTIONAL and MUST appear at most once
within the Link TLV (Type 2) that is itself carried within the
Traffic Engineering LSA specified in [RFC3630].
The OSPF NB-0-BW-LSP sub-TLV format is defined below:
Type (2 octets): To be assigned by IANA (suggested value = 19)
Length (2 octets): 4
Value (4 octets): number of unconstrained TE LSP(s) signalled across
the link.
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4. Elements of procedure
An implementation may decide to implement a dual-thresholds mechanism
to govern the origination of updated OSPF LSA or ISIS LSP. Similarly
to other MPLS Traffic Engineering link characteristics, LSA/LSP
origination trigger mechanisms are outside of the scope of this
document.
5. IANA Considerations
IANA will assign a new code point for the newly defined IS-IS sub-TLV
(NB-0-BW-LSP) carried within the TLV 22 (suggested value =19)
IANA will assign a new code point for the newly defined OSPF sub-TLV
(NB-0-BW-LSP) carried within the Link TLV (Type 2) of the Traffic
Engineering LSA (suggested value=19).
6. Security Considerations
This document raises no new security issues for IS-IS and OSPF.
7. Acknowledgements
The authors would like to thank Jean-Louis Le Roux for his useful
inputs.
8. References
8.1. Normative References
[I-D.ietf-isis-te-bis]
Li, T. and H. Smit, "IS-IS extensions for Traffic
Engineering", draft-ietf-isis-te-bis-00 (work in
progress), September 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
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8.2. Informative References
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
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Authors' Addresses
JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Email: jpv@cisco.com
Matthew R. Meyer
Global Crossing
3133 Indian Valley Tr.
Howell, MI 48855
USA
Email: mrm@gblx.net
Kenji Kumaki
KDDI Corporation
Garden Air Tower Iidabashi, Chiyoda-ku,
Tokyo, 102-8460
JAPAN
Email: ke-kumaki@kddi.com
Alberto Tempia Bonda
Telecom Italia
via G. Reiss Romoli 274
Torino, 10148
ITALIA
Email: alberto.tempiabonda@telecomitalia.it
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