Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                       Matthew. R. Meyer
Expires: May 18, 2008                                    Global Crossing
                                                               K. Kumaki
                                                        KDDI Corporation
                                                   Alberto. Tempia Bonda
                                                          Telecom Italia
                                                       November 15, 2007


 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-07

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Several Link-type sub-TLVs have been defined for OSPF and IS-IS in
   the context of Multiprotocol Label Switching (MPLS) Traffic



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   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 assumption
   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  . . . . . . . . . . 9



































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.  Terminology

   Terminology used in this document

   CSPF: Constraint 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


.  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 Router) 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 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 LSPs are used, such
   metrics (e.g. path cost, number of hops, ...) are usually ineffective
   and may lead to poorly load balanced traffic.



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   By making statistical assumption 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 Path (LSP) across a set of equal cost paths.  This
   requires knowledge of the number of unconstrained Traffic Engineering
   Label Switched Path(s) (TE LSP) 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 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 [RFC3784]) 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 [RFC3784] 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 are not included in the count that is reported.


.  Protocol extensions

   The Number of 0-bandwidth TE LSP(s) Sub-TLV is defined that specifies
   the number of TE LSPs signalled with zero bandwidth across a link.

3.1.  IS-IS

   The 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 [RFC3784].

   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




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   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 Number
   of 0-bandwidth TE LSP(s) 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.


.  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.


.  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
   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.




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   Suggested Value TLV Name Reference

   23 Unconstrained TE LSP Count (sub-)TLV This document


.  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 [RFC2470] for the base
   OSPF protocol and in [RFC1194] for IS-IS.


.  Acknowledgements

   The authors would like to thank Jean-Louis Le Roux, Adrian Farrel,
   Daniel King, Acee Lindem, Lou Berger, Attila Takacs and Loa Anderson
   for their useful inputs.


.  References

8.1.  Normative References

   [I-D.ietf-ospf-ospfv3-traffic]
              Ishiguro, K., "Traffic Engineering Extensions to OSPF
              version 3", draft-ietf-ospf-ospfv3-traffic-09 (work in
              progress), September 2007.

   [RFC1194]  Zimmerman, D., "Finger User Information Protocol",
              RFC 1194, November 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.

   [RFC2470]  Crawford, M., Narten, T., and S. Thomas, "Transmission of
              IPv6 Packets over Token Ring Networks", RFC 2470,
              December 1998.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              September 2003.

   [RFC3784]  Smit, H. and T. Li, "Intermediate System to Intermediate
              System (IS-IS) Extensions for Traffic Engineering (TE)",
              RFC 3784, June 2004.



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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.


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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