Open Shortest Path First                                        Z. Zhang
Internet-Draft                                                   L. Wang
Updates: 2328, 5340 (if approved)                 Juniper Networks, Inc.
Intended status: Standards Track                               A. Lindem
Expires: April 17, 2015                                    Cisco Systems
                                                               D. Dubois
                                                    General Dynamics C4S
                                                                V. Julka
                                                             T. McMillan
                                             L3 Communications, Linkabit
                                                        October 14, 2014

                          OSPF Two-part Metric


   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

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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

   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 April 17, 2015.

Copyright Notice

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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
     3.1.  Router Interface Parameters . . . . . . . . . . . . . . . . 4
     3.2.  Advertising Network-to-Router metric in OSPFv2  . . . . . . 5
     3.3.  Advertising Network-to-Router metric in OSPFv3  . . . . . . 5
     3.4.  SPF Calculation . . . . . . . . . . . . . . . . . . . . . . 5
     3.5.  Backward Compatibility  . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 8

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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 do 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 network, where no Network
   LSA is advertised and Router-LSAs simply include 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 where the metric between
   different pair of routers are really independent.  For example, VPLS

   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 goes 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 its
   communication capability degrades significantly.  Through the radio
   control protocol, all other routers determine that the metric to this
   particular router 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 needs 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 inhibit network scaling.

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 RFC 6845 hybrid interface type, the network
   is just treated as a regular broadcast network.  A router on the
   network no longer lists individual metrics to each neighbor in its
   Router-LSA.  Instead, each router advertises the metric from the
   network to itself in addition to the normal metric for the network.
   With the normal Router-to-Network and additional Network-to-Router
   metrics advertised for each router, individual router-to-router
   metric can be calculated.

   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
   the radio level (layer-2), at layer-3, the satellite does not
   participate in packet forwarding.  In fact, the satellite does not
   need to be running any layer-3 protocol.  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 herein.  This is ensured by procedures described
   in Section 3.5.

3.1.  Router Interface Parameters

   The "Router interface parameters" have the following additions:

   o  Two-part metric: TRUE if the interface connects to a multi-access
      network that uses two-part metric.  All routers connected to the
      same network SHOULD have the same configuration for their
      corresponding interfaces.

   o  Interface input cost: Link state metric from the two-part-metric
      network to this router.  Defaulted to "Interface output cost" but
      not valid for normal networks using a single metric.  May be
      configured or dynamically adjusted to a value different from the
      "Interface output cost".

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3.2.  Advertising Network-to-Router metric in OSPFv2

   For OSPFv2, the Network-to-Router metric is encoded in an OSPF
   Extended Link TLV Sub-TLV [ietf-ospf-lsa-extend], defined in this
   document as the Network-to-Router Metric Sub-TLV.  The type of the
   Sub-TLV is TBD.  The length of the Sub-TLV is 4 (for the value part
   only).  The value part of the Sub-TLV is defined as follows:

        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
       |      MT       |        0      |          MT   metric          |

   Multiple such Sub-TLVs can exist in a single OSPF Extended Link TLV,
   one for each topology.  The OSPF Extended Link TLV identifies the
   transit link to the network, and is part of an OSPFv2 Extended-Link
   Opaque LSA.  The Sub-TLV MUST ONLY appear in Extended-Link TLVs for
   Link Type 2 (link to transit network), and MUST be ignored if
   received for other link types.

3.3.  Advertising Network-to-Router metric in OSPFv3

   For OSPFv3, the same Network-to-Router Metric Sub-TLV definition is
   used, though it is part of the Router-Link TLV of E-Router-LSA [ietf-
   ospf-ospfv3-lsa-extend].  Currently OSPFv3 Multi-Toplogy is not
   defined so the only valid value for the MT field is 0 and only one
   such Sub-TLV SHOULD be included in the Router-Link TLV.  Received
   Sub-TLVs with non-zero MT field MUST be ignored.

   Similarly, the Sub-TLV MUST ONLY appear in Router-Link TLVs for Link
   Type 2 (connection to a transit network) and MUST be ignored if
   received for other link types.

3.4.  SPF Calculation

   During the first stage of shortest-path tree calculation for an area,
   when a vertex V corresponding to a Network-LSA is added to the
   shortest-path tree and its adjacent vertex W (joined by a link in V's
   corresponding Network LSA), the cost from V to W, which is W's
   network-to-router cost, is determined as follows:

   o  For OSPFv2, if vertex W has a corresponding Extended-Link Opaque
      LSA with an Extended Link TLV for the link from W to V, and the
      Extended Link TLV has a Network-to-Router Metric Sub-TLV for the
      corresponding topology, then the cost from V to W is the metric in
      the Sub-TLV.  Otherwise, the cost is 0.

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   o  For OSPFv3, if vertex W has a corresponding E-Router-LSA with a
      Router-Link TLV for the link from W to V, and the Router-Link TLV
      has a Network-to-Router Metric Sub-TLV, then the cost from V to W
      is the metric in the Sub-TLV.  If not, the cost is 0.

3.5.  Backward Compatibility

   Due to the change of procedures in the SPF calculation, all routers
   in an area that includes one or more two-part metric networks must
   support the changes specified in this document.  To ensure that, if
   an area is provisioned to support two-part metric networks, all
   routers supporting this capability must advertise a Router
   Information (RI) LSA with a Router Functional Capabilities TLV [acee-
   ospf-rfc4970bis] that includes the following Router Functional
   Capability Bit:

             Bit       Capabilities

             0         OSPF Two-part Metric [TPM]

   Upon detecting the presence of a reachable Router-LSA without a
   companion RI LSA that has the bit set, all routers MUST disable the
   two-part metric functionalities and take the following actions:

   o  If this router currently advertises network-to-router costs,
      remove the Network-to-Router Metric Sub-TLVs.  This may lead to
      removal of parent TLVs and even withdrawal of the parent LSAs.

   o  Recalculate routes w/o considering any network-to-router costs.

4.  IANA Considerations

   This document requests IANA to assigna a new bit in the Router
   Functional Capabilities TLV to indicate the capability of supporting
   two-part metric, a new Sub-TLV in the OSPF Extended-Link TLV Sub-TLV
   Registry, and a new Sub-TLV in the The OSPFv3 Extend-LSA Sub-TLV

5.  Security Considerations

   This document does not introduce new security risks.

6.  Acknowledgements

   The authors would like to thank Abhay Roy, Hannes Gredler, Peter
   Psenak and Eric Wu for their comments and suggestions.

7.  References

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7.1.  Normative References

   [I-D.acee-ospf-rfc4970bis]         Lindem, A., Shen, N., Vasseur, J.,
                                      Aggarwal, R., and S. Shaffer,
                                      "Extensions to OSPF for
                                      Advertising Optional Router
                                      (work in progress), July 2014.

   [I-D.ietf-ospf-lsa-extend]         Psenak, P., Previdi, S., Filsfils,
                                      C., Gredler, H., Shakir, R.,
                                      Henderickx, W., Tantsura, J., and
                                      A. Lindem, "OSPFv2 LSA
                                      (work in progress), August 2014.

   [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-04 (work in
                                      progress), September 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.

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7.2.  Informative References

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

Authors' Addresses

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


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


   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC 27513


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


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


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


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