Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems, Inc
Intended status: Standards Track Matthew. R. Meyer
Expires: March 5, 2009 Global Crossing
K. Kumaki
KDDI Corporation
Alberto. Tempia Bonda
Telecom Italia
September 1, 2008
A Link-Type sub-TLV to convey the number of Traffic Engineering Label
Switched Paths signalled with zero reserved bandwidth across a link
draft-ietf-mpls-number-0-bw-te-lsps-12
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Abstract
Several Link-type sub-Type-Lenght-Values (sub-TLVs) have been defined
for Open Shortest Path First (OSPF) and Intermediate System to
Intermediate System (IS-IS) in the context of Multiprotocol Label
Switching (MPLS) Traffic Engineering (TE) in order to advertise some
link characteristics such as the available bandwidth, traffic
engineering metric, administrative group and so on. By making
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statistical assumptions about the aggregated traffic carried onto a
set of TE Label Switched Paths (LSPs) signalled with zero bandwith
(referred to as unconstrained TE LSP in this document), and with the
knowledge of the number of unconstrained TE LSPs signalled across a
link, algorithms can be designed to load balance (existing or newly
configured) unconstrained TE LSP across a set of equal cost paths.
This requires knowledge of the number of unconstrained TE LSPs
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].
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol extensions . . . . . . . . . . . . . . . . . . . . . 5
3.1. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. OSPF . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Elements of procedure . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Terminology
Terminology used in this document
CSPF: Constrained Shortest Path First
IGP : Interior Gateway Protocol
LSA: Link State Advertisement
LSP: Link State Packet
MPLS: Multiprotocol Label Switching
LSR: Label Switching Router
SRLG: Shared Risk Link Group
TE LSP: Traffic Engineering Label Switched Path
Unconstrained TE LSP: A TE LSP signalled with a bandwidth equal to 0
2. Introduction
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 TE LSPs signalled with
zero bandwidth (also referred to as unconstrained TE LSP in this
document) between a set of LSRs (Label Switching Routers) and
protecting these TE LSPs against link, SRLG (Shared Risk Link Group)
and/or node failures with pre-established backup tunnels. The
traffic routed onto such unconstrained TE LSPs simply follows the IGP
shortest path (since the TE LSP computed by the path computation
algorithm (e.g. CSPF) will be no different than the IGP (Interior
Gateway Protocol) shortest path should the TE metric be equal to the
IGP metric) but is protected with MPLS TE Fast Reroute.
When a reoptimization process is triggered for an existing TE LSP,
the decision on whether to reroute that TE LSP onto a different path
is governed by the discovery of a lower cost path satisfying the
constraints (other metrics such that the percentage of reserved
bandwidth or the number of hops can also be used). Unfortunately,
metrics such as the path cost or the number of hops may be
ineffective in various circumstances: for example, in the case of a
symmetrical network with ECMPs (Equal Cost Multi-Paths), if the
network operator uses unconstrained TE LSP, this may lead to a poorly
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load balanced traffic: indeed, several paths between a source and a
destination of a TE LSP may exist that have the same cost and the
reservable amount of bandwidth along each path cannot be used as a
tie-breaker.
By making statistical assumptions about the aggregated traffic
carried by a set of TE LSPs signalled with no bandwidth requirement
(referred to as unconstrained TE LSPs in this document), algorithms
can be designed to load balance (existing or newly configured)
unconstrained TE Label Switched Paths (LSPs) across a set of equal
cost paths. This requires knowledge of the number of unconstrained
Traffic Engineering Label Switched Paths (TE LSPs) signalled across
each link.
Note that the specification of load balancing algorithms is outside
the scope of this document and is referred to 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, for
example to evaluate the number of affected unconstrained TE LSPs in
case of a link failure.
A set of Link-type sub-TLVs have been defined for OSPF and IS-IS (see
[RFC3630] and [I-D.ietf-isis-te-bis]) 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. 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 LSPs signalled across a link.
Unconstrained TE LSPs that are configured and provisioned through a
management system MAY be omitted from the count that is reported.
3. Protocol extensions
Two Unconstrained TE LSP count sub-TLVs are defined that specify the
number of TE LSPs signalled with zero bandwidth across a link.
3.1. IS-IS
The IS-IS Unconstrained TE LSP Count Sub-TLV is OPTIONAL and MUST NOT
appear more than once within the extended IS reachability TLV (type
22) specified in [I-D.ietf-isis-te-bis] or the MT Intermediate
Systems TLV (type 222) specified in [RFC5120]. If a second instance
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of the Unconstrained TE LSP Count sub-TLV is present, the receiving
system MUST only process the first instance of the sub-TLV.
The IS-IS Unconstrained TE LSP Count Sub-TLV format is defined below:
Type (1 octet): To be assigned by IANA (suggested value = 23)
Length (1 octet): 2
Value (2 octets): number of unconstrained TE LSP(s) signalled across
the link.
3.2. OSPF
The OSPF Unconstrained TE LSP Count TLV is OPTIONAL and MUST NOT
appear more than once within the Link TLV (Type 2) that is itself
carried within the Traffic Engineering LSA specified in [RFC3630] or
the OSPFv3 Intra-Area-TE LSA (function code 10) defined in
[I-D.ietf-ospf-ospfv3-traffic]. If a second instance of the
Unconstrained TE LSP Count sub-TLV is present, the receiving system
MUST only process the first instance of the sub-TLV.
The OSPF Unconstrained TE LSP Count Sub-TLV format is defined below:
Type (2 octets): To be assigned by IANA (suggested value = 23)
Length (2 octets): 4
Value (4 octets): number of unconstrained TE LSP(s) signalled across
the link.
4. Elements of procedure
The absence of the Unconstrained TE LSP Count (sub-)TLV SHOULD be
interpreted as an absence of information about the link.
Similarly to other MPLS Traffic Engineering link characteristics,
LSA/LSP origination trigger mechanisms are outside the scope of this
document. Care must be given to not trigger the systematic flooding
of a new IS-IS LSP or OSPF LSA with a too high granularity in case of
change of the number of unconstrained TE LSPs.
5. IANA Considerations
IANA has defined a sub-registry for the sub-TLVs carried in the IS-IS
TLV 22. IANA is requested to assign a new TLV code-point for the
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Unconstrained TE LSP Count sub-TLV carried within the TLV 22.
Suggested Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV This document
IANA has defined a sub-registry for the sub-TLVs carried in an OSPF
TE Link TLV (type 2). IANA is requested to assign a new sub-TLV
code-point for the Unconstrained TE LSP Count sub-TLV carried within
the TE Link TLV.
Suggested Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV This document
6. Security Considerations
The function described in this document does not create any new
security issues for the OSPF and the IS-IS protocols. Security
considerations are covered in [RFC2328] and [RFC5340] for the base
OSPF protocol and in [RFC1195] and [I-D.ietf-isis-rfc3567bis] for
IS-IS.
A security framework for MPLS and Generalized MPLS can be found in
[I-D.ietf-mpls-mpls-and-gmpls-security-framework].
7. Acknowledgements
The authors would like to thank Jean-Louis Le Roux, Adrian Farrel,
Daniel King, Acee Lindem, Lou Berger, Attila Takacs, Pasi Eronen,
Russ Housley, Tim Folk and Loa Anderson for their useful inputs.
8. References
8.1. Normative References
[I-D.ietf-isis-rfc3567bis]
Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic
Authentication", draft-ietf-isis-rfc3567bis-03 (work in
progress), July 2008.
[I-D.ietf-isis-te-bis]
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Li, T. and H. Smit, "IS-IS extensions for Traffic
Engineering", draft-ietf-isis-te-bis-00 (work in
progress), April 2008.
[I-D.ietf-ospf-ospfv3-traffic]
Ishiguro, K., Manral, V., Davey, A., and A. Lindem,
"Traffic Engineering Extensions to OSPF version 3",
draft-ietf-ospf-ospfv3-traffic-13 (work in progress),
June 2008.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
8.2. Informative References
[I-D.ietf-mpls-mpls-and-gmpls-security-framework]
Fang, L. and M. Behringer, "Security Framework for MPLS
and GMPLS Networks",
draft-ietf-mpls-mpls-and-gmpls-security-framework-03 (work
in progress), July 2008.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
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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: mrminc@gmail.com
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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