OSPF Two-Part Metric
draft-ietf-ospf-two-part-metric-10

Network Working Group                                           Z. Zhang
Internet-Draft                                                   L. Wang
Updates: 2328 (if approved)                       Juniper Networks, Inc.
Intended status: Standards Track                               A. Lindem
Expires: April 16, 2017                                    Cisco Systems
                                                        October 13, 2016

                          OSPF Two-part Metric
                 draft-ietf-ospf-two-part-metric-10.txt

Abstract

   This document specifies an optional OSPF protocol extension to
   represent router metrics in a multi-access network in two parts: the
   metric from the router to the network and the metric from the network
   to the router.  For such networks, the router to router metric for
   OSPF route computation is the sum of the two parts.  This document
   updates RFC 2328.

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
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   This Internet-Draft will expire on April 16, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   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 Traffic Engineering (TE)
           Metric  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  Advertising Network-to-Router Metric in OSPFv3  . . . . .   5
     3.5.  OSPF Stub Router Behavior . . . . . . . . . . . . . . . .   5
     3.6.  SPF Calculation . . . . . . . . . . . . . . . . . . . . .   6
     3.7.  Backward Compatibility  . . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   8
   Appendix B.  Contributors' Addreses . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   With Open Shortest Path First (OSPF, [RFC2328], [RFC5340]) Link State
   Advertisements (LSAs), 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.  [RFC6845] 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.

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   That works well for broadcast networks where the metric between
   different pair of routers are really independent.  For example,
   Virtual Private LAN Service (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 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), [RFC6845] 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.

1.1.  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].

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
   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 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

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   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 3.7.

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 [RFC7684], defined in this document as the
   Network-to-Router Metric Sub-TLV.  The type of the Sub-TLV is TBD2.
   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-ID    |        0      |          MT Metric            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Multiple such Sub-TLVs can exist in a single OSPF Extended Link TLV,
   one for each topology [RFC4915].  Each Sub-TLV will have a unique
   Multi-Topology Identifier (MT-ID) and will adhere to the
   advertisement rules defined in section 3.4 of [RFC4915].  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 Traffic Engineering (TE) Metric

   A Traffic Engineering Network-to-Router Metric Sub-TLV is defined,
   similar to the Traffic Engineering Metric Sub-TLV defined in
   Section 2.5.5 of [RFC3630].  The only difference is the TLV type,
   which is TBD3.  The Sub-TLV MUST only appear in type 2 Link TLVs
   (Multi-access) of Traffic Engineer LSAs (OSPF2) or Intra-Area-TE-LSAs
   (OSPFv3) [RFC5329], and MUST appear at most once in such Link TLV.

3.4.  Advertising Network-to-Router Metric in OSPFv3

   Network-to-Router metric advertisement in OSPFv3 Extended-Router-LSA
   [I-D.ietf-ospf-ospfv3-lsa-extend] will be described in a separate
   document.

3.5.  OSPF Stub Router Behavior

   When an OSPF router with interfaces including two-part metric is
   advertising itself as a stub router [RFC6987], only the Router-to-
   Network metric in the stub router's OSPF Router-LSA links is set to
   the MaxLinkMetric.  This is fully backward compatible and will result
   in the same behavior as [RFC6987].

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3.6.  SPF Calculation

   The first stage of the shortest-path tree calculation is described in
   section 16.1 of [RFC2328].  With two-part metric, when a vertex V
   corresponding to a Network-LSA has just been added to the Shortest
   Path Tree (SPT) and an adjacent vertex W (joined by a link in V's
   corresponding Network-LSA) is being added to the candidate list, the
   cost from V to W (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.

   o  OSPFv3 [RFC5340] SPF changes will be described in a separate
      document.

3.7.  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
   [RFC7770]  that includes the following Router Functional Capability
   Bit:

             Bit       Capabilities

             TBD1      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 recalculate
   routes without considering any network-to-router costs.

4.  IANA Considerations

   This document requests the following IANA assignments:

   o  A new bit (TBD1) in Registry for OSPF Router Informational
      Capability Bits, to indicate the capability of supporting two-part
      metric.

   o  A new Sub-TLV type (TBD2) in OSPF Extended Link TLV Sub-TLV
      registry, for the Network-to-Router Metric Sub-TLV.

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   o  A new Sub-TLV type (TBD3) in Types for sub-TLVs of TE Link TLV
      (Value 2) registry, for the Network-to-Router TE Metric Sub-TLV.

5.  Security Considerations

   This document does not introduce new security risks.  Existing
   security considerations in OSPFv2 and OSPFv3 apply.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <http://www.rfc-editor.org/info/rfc3630>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <http://www.rfc-editor.org/info/rfc4915>.

   [RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
              "Traffic Engineering Extensions to OSPF Version 3",
              RFC 5329, DOI 10.17487/RFC5329, September 2008,
              <http://www.rfc-editor.org/info/rfc5329>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <http://www.rfc-editor.org/info/rfc7684>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <http://www.rfc-editor.org/info/rfc7770>.

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6.2.  Informative References

   [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-12
              (work in progress), September 2016.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <http://www.rfc-editor.org/info/rfc5340>.

   [RFC6845]  Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
              and Point-to-Multipoint Interface Type", RFC 6845,
              DOI 10.17487/RFC6845, January 2013,
              <http://www.rfc-editor.org/info/rfc6845>.

   [RFC6987]  Retana, A., Nguyen, L., Zinin, A., White, R., and D.
              McPherson, "OSPF Stub Router Advertisement", RFC 6987,
              DOI 10.17487/RFC6987, September 2013,
              <http://www.rfc-editor.org/info/rfc6987>.

Appendix A.  Acknowledgements

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

   The RFC text was produced using Marshall Rose's xml2rfc tool.

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Appendix B.  Contributors' Addreses

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

   EMail: dave.dubois@gd-ms.com

   Vibhor Julka
   Individual

   EMail: vjulka1@yahoo.com

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

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

Authors' Addresses

   Zhaohui 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

   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC 27513

   Email: acee@cisco.com

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