Network Working Group JP. Vasseur, Ed.
Request for Comments: 5330 Cisco Systems, Inc
Category: Standards Track M. Meyer
BT
K. Kumaki
KDDI R&D Labs
A. Bonda
Telecom Italia
October 2008
A Link-Type sub-TLV to Convey the Number of
Traffic Engineering Label Switched Paths Signalled with
Zero Reserved Bandwidth across a Link
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
Several Link-type sub-Type-Length-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
statistical assumptions about the aggregated traffic carried onto a
set of TE Label Switched Paths (LSPs) signalled with zero bandwidth
(referred to as "unconstrained TE LSP" in this document), 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 LSPs
signalled across a link.
Vasseur, et al. Standards Track [Page 1]
RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................3
2.1. Requirements Language ......................................4
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 ................................................6
8. References ......................................................6
8.1. Normative References .......................................6
8.2. Informative References .....................................6
1. 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, but is protected with MPLS TE Fast Reroute. This is
because 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.
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 as 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
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.
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RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
By making statistical assumptions about the aggregated traffic
carried by a set of unconstrained TE LSPs, algorithms can be designed
to load balance (existing or newly configured) unconstrained TE LSPs
across a set of equal cost paths. This requires knowledge of the
number of unconstrained 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 [RFC5305]) 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 [RFC5305],
the information related to the number of unconstrained TE LSPs 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.
2. 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
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RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
Unconstrained TE LSP: A TE LSP signalled with a bandwidth equal to 0
2.1. 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].
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 [RFC5305] or the Multi-Topology (MT) Intermediate
Systems TLV (type 222) specified in [RFC5120]. 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 IS-IS Unconstrained TE LSP Count sub-TLV format is defined below:
Type (1 octet): 23
Length (1 octet): 2
Value (2 octets): number of unconstrained TE LSPs signalled across
the link.
3.2. OSPF
The OSPF Unconstrained TE LSP Count sub-TLV is OPTIONAL and MUST NOT
appear more than once within the Link TLV (Type 2) that is itself
carried within either the Traffic Engineering LSA specified in
[RFC3630] or the OSPFv3 Intra-Area-TE LSA (function code 10) defined
in [RFC5329]. 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.
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RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
The OSPF Unconstrained TE LSP Count sub-TLV format is defined below:
Type (2 octets): 23
Length (2 octets): 4
Value (4 octets): number of unconstrained TE LSPs 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.
Similar 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 in 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 and has assigned a new TLV codepoint for the Unconstrained TE
LSP Count sub-TLV carried within the TLV 22.
Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV RFC 5330
IANA has defined a sub-registry for the sub-TLVs carried in an OSPF
TE Link TLV (type 2) and has assigned a new sub-TLV codepoint for the
Unconstrained TE LSP Count sub-TLV carried within the TE Link TLV.
Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV RFC 5330
6. Security Considerations
The function described in this document does not create any new
security issues for the OSPF and IS-IS protocols. Security
considerations are covered in [RFC2328] and [RFC5340] for the base
OSPF protocol and in [RFC1195] and [RFC5304] for IS-IS.
A security framework for MPLS and Generalized MPLS can be found in
[G/MPLS].
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RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
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 Polk, and Loa Anderson for their useful inputs.
8. References
8.1. Normative References
[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.
[RFC5304] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication",
RFC 5304, October 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3", RFC
5329, September 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
8.2. Informative References
[G/MPLS] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", Work In Progress, July 2008.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "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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RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
Authors' Addresses
JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: jpv@cisco.com
Matthew R. Meyer
BT
Boston, MA
USA
EMail: matthew.meyer@bt.com
Kenji Kumaki
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Fujimino
Saitama 356-8502, JAPAN
EMail: ke-kumaki@kddi.com
Alberto Tempia Bonda
Telecom Italia
via G. Reiss Romoli 274
Torino, 10148
ITALIA
EMail: alberto.tempiabonda@telecomitalia.it
Vasseur, et al. Standards Track [Page 7]
RFC 5330 Sub-TLV for Unconstrained TE LSP October 2008
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Vasseur, et al. Standards Track [Page 8]