RFC5330
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.
Contents
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.
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.
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
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.
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.
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.
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.
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.
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.
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
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].
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.
References
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.
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.
Authors' Addresses
JP Vasseur (editor) Cisco Systems, Inc 1414 Massachusetts Avenue Boxborough, MA 01719 USA
EMail: [email protected]
Matthew R. Meyer BT Boston, MA USA
EMail: [email protected]
Kenji Kumaki KDDI R&D Laboratories, Inc. 2-1-15 Ohara Fujimino Saitama 356-8502, JAPAN
EMail: [email protected]
Alberto Tempia Bonda Telecom Italia via G. Reiss Romoli 274 Torino, 10148 ITALIA
EMail: [email protected]
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