Open Shortest Path First                                        Z. Zhang
Internet-Draft                                                   L. Wang
Updates: 2328, 5340 (if approved)                 Juniper Networks, Inc.
Intended status: Standards Track                               D. Dubois
Expires: August 17, 2014                            General Dynamics C4S
                                                                V. Julka
                                                             T. McMillan
                                             L3 Communications, Linkabit
                                                       February 13, 2014


                          OSPF Two-part Metric
                draft-zzhang-ospf-two-part-metric-01.txt

Abstract

   This document specifies an optional extension to the OSPF protocol,
   to represent the metric on a multi-access network as two parts: the
   metric from a router to the network, and the metric from the network
   to the router.  The router to router metric would be the sum of the
   two.

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 RFC2119.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 17, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Proposed Enhancement  . . . . . . . . . . . . . . . . . . . . . 3
   3.  Speficications  . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 7





























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1.  Introduction

   For a broadcast network, a Network LSA is advertised to list all
   routers on the network, and each router on the network includes a
   link in its Router LSA to describe its connection to the network.
   The link in the Router LSA includes a metric but the listed routers
   in the Network LSA does not include a metric.  This is based on the
   assumption that from a particular router, all others on the same
   network can be reached with the same metric.

   With some broadcast networks, different routers can be reached with
   different metrics.  RFC 6845 extends the OSPF protocol with a hybrid
   interface type for that kind of broadcast networks, with which no
   Network LSA is used and routers simply includes p2p links to all
   routers on the same network with individual metrics.  Broadcast
   capability is still utilized to optimize database synchronization and
   adjacency maintenance.

   That works well for broadcast networks on which metric between
   different pair of routers are really independent.  For example, VPLS
   networks.

   With certain types of broadcast networks, further optimization can be
   made to reduce the size of the Router LSAs and number of updates.

   Consider a satellite radio network with fixed and mobile ground
   terminals.  All communication go through the satellite.  When the
   mobile terminals move about, their communication capability may
   change.  When OSPF runs over the radio network (routers being or in
   tandem with the terminals), RFC 6845 hybrid interface can be used,
   but with the following drawbacks.

   Consider that one terminal/router moves into an area where
   communication capability degrades significantly.  Through the radio
   control protocol all other routers determine that the metric to this
   particular one changed and they all need to update their Router LSAs
   accordingly.  The router in question also determines that its metric
   to reach all others also changed and it also need to update its
   Router LSA.  Consider that there could be many terminals and many of
   them can be moving fast and frequently, the number/frequency of
   updates of those large Router LSAs could become inhibiting.

2.  Proposed Enhancement

   Notice that in the above scenario, when one terminal's communication
   capability changes, its metric to all other terminals and the metric
   from all other terminals to it will all change in a similar fashion.
   Given this, the above problem can be easily addressed by breaking the



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   metric into two parts: the metric to the satellite and the metric
   from the satellite.  The metric from terminal R1 to R2 would be the
   sum of the metric from R1 to the satellite and the metric from the
   satellite to R2.

   Now instead of using the RFC6845 hybrid interface type, the network
   is just treated as a regular broadcast one.  A router on the network
   no longer needs to list individual metrics to each neighbors in its
   Router LSA.  In case of symmetric metric to/from the satellite, it is
   represented by the transit link's metric in the Router LSA.  In case
   of asymetric metric, it is rerepresented by a special MT Metric
   (Section 3).

   With the proposed enhancement, the size of Router LSA will be
   significantly reduced.  In addition, when a router's communication
   capability changes, only that router needs to update its Router LSA.

   Note that while the example uses the satellite as the relay point at
   radio level (layer 2), at layer 3 the satellite does not play any
   role.  It does not need to be running layer 3 protocol at all.
   Therefore for generality, the metric is abstracted as to/from the
   "network" rather that specifically to/from the "satellite".

3.  Speficications

   The following protocol specifications are added to or modified from
   the base OSPF protocol.  If an area contains one or more two-part
   metric networks, then all routers in the area must support the
   extensions specified here.  This document does not currently specify
   a way to detect a router's capability of supporting this, and relies
   on operator's due diligence in provisioning.  A protocol mechanism
   may be developer in the future.

   The "Router interface parameters" has the following additions:

   o  Two-part metric: TRUE if the interface connects to a multi-access
      network that uses two-part metric.

   o  Interface input cost: Link state metric from the network to this
      router.  Defaulted to "Interface output cost".  May be configured
      or dynamically adjusted to a value different from the "Interface
      output cost".  If different from the output cost, it MUST be
      advertised in addition to the link (output) cost for this
      interface in the router's Router LSA.

   To signal that a network is using Two-part Metric, a new Link Type X
   (value TBD) is added.  It is similar to Type 2, except that the
   network uses Two-part Metric, and there may be an optional network-



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   to-router metric (interface input cost).


   Link type   Description       Link ID
   --------------------------------------------
       X       Link to transit   Interface of
               network that uses the Designated
               Two-part Metric   Router

   For backward compatibility, if Two-Part Metric is to be used in an
   area, all routers in the area must support it.  To ensure this, a new
   bit 0x00000004 (pending WG consensus and IANA assignment) in the LLS
   EOF-TLV [RFC5613] is used:


     Bit                     Name                        Reference
     0x00000001              LSDB Resynchronization (LR) [RFC4811]
     0x00000002              Restart Signal (RS-bit)     [RFC4812]
     0x00000004              Two-Part Metric (TM-bit)    [this document]

   Each router must be configured to include in its Hello packets an
   EOF-TLV with the bit set, and any Hello packet without the EOF-TLV or
   without the bit set must be ignored.  With this, a router that does
   not support Two-Part Metric will never receive a Router LSA
   containing the new Link Type X.

   For the network-to-router metric (interface input cost) that is
   different from the router-to-network metric (interface output cost),
   with OSPFv2 it is carried in an MT-ID field ([RFC4915]):


   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Link ID                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Link Data                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     # MT-ID   |            metric             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     MT-ID     |             |1|          MT-ID  metric        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              ...                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   With OSPFv3, it is carried in a Router Multi-Topology sub-TLV:







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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          1 (RMT-sTLV)         |           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    MT-ID      |       0     |1|          MT-ID metric         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   .                                                               .
   .                            sub-TLVs                           .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   As illustrated above for both cases, the least significant bit of the
   field between MT-ID and MT-ID metric fields can be set to indicate
   that this is the network-to-router metric for the corresponding
   topology.  It is clear that this scheme is compatible with multi-
   topology.

   During intra-area SPF calculation, when a vertex W corresponding to a
   Network LSA is added to the candidate list because of a Type X link
   in a Router LSA for vertex V (that was just added to the shortest-
   path tree), W is marked that it uses Two-part Metric.  Later, when a
   vertex V marked with Two-part Metric (which must correspond to a
   Network LSA) is added to the shortest-path tree, for the vertex W
   that is reached via a link in V's corresponding LSA, the exact
   reverse link (of Type X) from W to V is located from W's
   corresponding Router LSA.  If the reverse link does not exist, W is
   not considered and the next link in V is checked.  If the reverse
   link has a network-to-router metric, that metric is used as the link
   cost between V and W. Otherwise, that reverse link's (default) metric
   is used as the link cost beteen V and W.

4.  IANA Considerations

   This document makes no request of IANA (unless the Link Type values
   in Router LSAs are assigned by IANA).

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

5.  Security Considerations

   This document does not introduce new security risks.

6.  References






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6.1.  Normative References

   [I-D.ietf-ospf-mt-ospfv3]          Mirtorabi, S. and A. Roy, "Multi-
                                      topology routing in OSPFv3 (MT-
                                      OSPFv3)",
                                      draft-ietf-ospf-mt-ospfv3-03 (work
                                      in progress), July 2007.

   [I-D.ietf-ospf-ospfv3-lsa-extend]  Lindem, A., Mirtorabi, S., Roy,
                                      A., and F. Baker, "OSPFv3 LSA
                                      Extendibility", draft-ietf-ospf-
                                      ospfv3-lsa-extend-01 (work in
                                      progress), February 2014.

   [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.

   [RFC4915]                          Psenak, P., Mirtorabi, S., Roy,
                                      A., Nguyen, L., and P. Pillay-
                                      Esnault, "Multi-Topology (MT)
                                      Routing in OSPF", RFC 4915,
                                      June 2007.

   [RFC5340]                          Coltun, R., Ferguson, D., Moy, J.,
                                      and A. Lindem, "OSPF for IPv6",
                                      RFC 5340, July 2008.

   [RFC5613]                          Zinin, A., Roy, A., Nguyen, L.,
                                      Friedman, B., and D. Yeung, "OSPF
                                      Link-Local Signaling", RFC 5613,
                                      August 2009.

6.2.  Informative References

   [RFC6845]                          Sheth, N., Wang, L., and J. Zhang,
                                      "OSPF Hybrid Broadcast and Point-
                                      to-Multipoint Interface Type",
                                      RFC 6845, January 2013.








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Authors' Addresses

   Jeffrey Zhang
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, MA 01886

   EMail: zzhang@juniper.net


   Lili Wang
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, MA 01886

   EMail: liliw@juniper.net


   David Dubois
   General Dynamics C4S
   400 John Quincy Adams Road
   Taunton, MA 02780

   EMail: dave.dubois@gdc4s.com


   Vibhor Julka
   L3 Communications, Linkabit
   9890 Towne Centre Drive
   San Diego, CA 92121

   EMail: vibhor.julka@l-3Com.com


   Tom McMillan
   L3 Communications, Linkabit
   9890 Towne Centre Drive
   San Diego, CA 92121

   EMail: tom.mcmillan@l-3com.com











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