Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                       Matthew. R. Meyer
Expires: June 15, 2007                                   Global Crossing
                                                               K. Kumaki
                                                        KDDI Corporation
                                                   Alberto. Tempia Bonda
                                                          Telecom Italia
                                                       December 12, 2006


 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-05

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Copyright Notice

   Copyright (C) The Internet Society (2006).

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 on
   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 the 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 . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9



































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.  Terminology

   Terminology used in this document

   CSPF: Constraint Shortest Path First

   MPLS: Multiprotocol Label Switching

   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.


.  Introduction

   It is not uncommon to deploy MPLS TE 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 (TE LSP signalled
   with zero bandwidth) between a set of LSRs and protecting these TE
   LSPs against link, SRLG and/or node failures with pre-established
   backup tunnels.  The traffic routed onto such unconstrained TE LSP
   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 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 are usually ineffective and may lead to poorly load balanced
   traffic.

   By making statistical assumption on the aggregated traffic carried
   onto a set of TE LSPs signalled with no bandwidth requirement
   (referred to as unconstrained TE LSP 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



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   paths.  This requires the knowledge of the number of unconstrained
   Traffic Engineering Label Switched Path(s) (TE LSP) signalled across
   a link.

   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.

   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.

   TE LSPs signalled with zero bandwidth that are configured and
   provisioned through a management system are not included in the count
   that is reported.

   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).


.  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 Number of 0-bandwidth TE LSP(s) sub-TLV is OPTIONAL and MUST
   appear at most once within the extended IS reachability TLV (type 22)
   specified in [RFC3784].

   The IS-IS Number of 0-bandwidth TE LSP(s) sub-TLV format is defined
   below:

   Type (1 octet): To be assigned by IANA (suggested value = 18)

   Length (1 octet): 2

   Value (2 octets): number of unconstrained TE LSP(s) signalled across
   the link.



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3.2.  OSPF

   The Number of 0-bandwidth TE LSP(s) 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] or
   the OSPFv3 Intra-Area-TE LSA (function code 10) defined in
   draft-ietf-ospf-ospfv3-traffic-07.txt.  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 Number of 0-bandwidth TE LSP(s) sub-TLV format is defined
   below:

   Type (2 octets): To be assigned by IANA (suggested value = 18)

   Length (2 octets): 4

   Value (4 octets): number of unconstrained TE LSP(s) signalled across
   the link.


.  Elements of procedure

   An implementation MAY decide to implement a dual-thresholds mechanism
   based on the number of unconstrained TE LSPs 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.


.  IANA Considerations

   IANA will assign a new code point for the newly defined IS-IS Number
   of 0-bandwidth TE LSP(s) sub-TLV carried within the TLV 22 (suggested
   value =18).

   IANA will assign a new code point for the newly defined OSPF Number
   of 0-bandwidth TE LSP(s) sub-TLV carried within the Link TLV (Type 2)
   of the Traffic Engineering LSA (suggested value=18).


.  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.




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.  Acknowledgements

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


.  References

8.1.  Normative References

   [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.

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.

   [OSPFv3-TE] Lindem, A. et al., "Traffic Engineering Extensions to OSPF
               version 3", draft-ietf-ospf-ospfv3-traffic, work in progress.

Authors' Addresses

   JP Vasseur (editor)
   Cisco Systems, Inc
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Email: jpv@cisco.com





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   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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