Network Working Group                                          P. Psenak
Internet-Draft                                                 A. Lindem
Intended status: Standards Track                           Cisco Systems
Expires: January 25, 2016                                  W. Henderickx
                                                          Alcatel-Lucent
                                                             J. Tantsura
                                                                Ericsson
                                                              H. Gredler
                                                  Juniper Networks, Inc.
                                                           July 24, 2015


          OSPFv2 Link Traffic Engineering (TE) Attribute Reuse
              draft-ppsenak-ospf-te-link-attr-reuse-00.txt

Abstract

   Various link attributes have been defined in OSPFv2 in the context of
   the MPLS Traffic Engineering (TE) and GMPLS.  Many of these link
   attributes can be used for purposes other than MPLS Traffic
   Engineering or GMPLS.  This documents defines how to distribute such
   attributes in OSPFv2 for applications other than MPLS Traffic
   Engineering or GMPLS purposes.

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 January 25, 2016.

Copyright Notice

   Copyright (c) 2015 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
   2.  Link attributes examples  . . . . . . . . . . . . . . . . . .   3
   3.  Advertising Link Attributes . . . . . . . . . . . . . . . . .   3
     3.1.  TE Opaque LSA . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Extended Link Opaque LSA  . . . . . . . . . . . . . . . .   4
     3.3.  Proposed solution . . . . . . . . . . . . . . . . . . . .   5
   4.  Reused TE link attributes . . . . . . . . . . . . . . . . . .   5
     4.1.  Remote interface IP address . . . . . . . . . . . . . . .   5
     4.2.  Link Local/Remote Identifiers . . . . . . . . . . . . . .   6
     4.3.  Shared Risk Link Group (SRLG) . . . . . . . . . . . . . .   6
     4.4.  Extended Metrics  . . . . . . . . . . . . . . . . . . . .   6
   5.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Various link attributes have been defined in OSPFv2 [RFC2328] in the
   context of the MPLS traffic engineering and GMPLS.  All these




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   attributes are distributed by OSPFv2 as a sub-TLVs of the Link-TLV
   advertised in the OSPFv2 TE Opaque LSA [RFC3630].

   Many of these link attributes are useful outside of the traditional
   MLPLS Traffic Engineering or GMPLS.  This brings its own set of
   problems, in particular how to distribute these link attributes in
   OSPFv2 when MPLS TE or GMPLS are not deployed or are deployed in
   parallel with other applications that use these link attributes.

1.1.  Requirements notation

   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.  Link attributes examples

   This section lists some of the link attributes originally defined for
   MPLS Traffic Engineering that can be used for other purposes in
   OSPFv2.  The list doesn't necessarily contain all the required
   attributes.

   1.  Remote Interface IP address [RFC3630] - OSPFv2 currently cannot
       distinguish between parallel set of links between two remote
       OSPFv2 routers.  As a result, the two-way connectivity check
       performed during SPF may succeed when the two routers disagree on
       which of the links to use for data traffic.

   2.  Link Local/Remote Identifiers - [RFC4203] - Used for the two-way
       connectivity check for parallel unnumbered links.  Also used for
       identifying adjacencies for unnumbered links in Segment Routing
       traffic engineering.

   3.  Shared Risk Link Group (SRLG) [RFC4203]  - In IPFRR, the SRLG is
       used to compute diverse backup paths [RFC5714].

   4.  Unidirectional Link Delay/Loss Metrics [RFC7471] - Could be used
       for the shortest path first (SPF) computation using alternate
       metrics within an OSPF area.

3.  Advertising Link Attributes

   This section outlines possible approaches for advertising link
   attributes originally defined for MPLS Traffic Engineering purposes
   or GMPLS when they are used for other applications.






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3.1.  TE Opaque LSA

   One approach for advertising link attributes is to continue to use TE
   Opaque LSA ([RFC3630]).  There are several problems with this
   approach:

   1.  Whenever the link is advertised in a TE Opaque LSA, the link
       becomes a part of the TE topology, which may not match IP routed
       topology.  By making the link part of the TE topology, remote
       nodes may mistakenly believe that the link is available for MPLS
       TE or GMPLS, when, in fact, MPLS is not enabled on the link.

   2.  The TE Opaque LSA carries link attributes that are not used or
       required by MPLS TE or GMPLS.  There is no mechanism in TE Opaque
       LSA to indicate which of the link attributes should be passed to
       MPLS TE application and which should be used by OSPFv2 and other
       applications.

   3.  Link attributes used for non-TE purposes is partitioned across
       multiple LSAs - the TE Opaque LSA and the Extended Link Opaque
       LSA.  This partitioning will require implementations to lookup
       multiple LSAs to extract link attributes for a single link,
       bringing needless complexity to the OSPFv2 implementations.

   The advantage of this approach is that there is no additional
   standardization requirement to advertise the TE/GMPL attributes for
   other applications.  Additionally, link attributes are only
   advertised once when both OSPF TE and other applications are deployed
   on the same link.  This is not expected to be a common deployment
   scenario.

3.2.  Extended Link Opaque LSA

   An alternative approach for advertising link attributes is to use
   Extended Link Opaque LSAs as defined in
   [I-D.ietf-ospf-prefix-link-attr].  This LSA was defined as a generic
   container for distribution of the extended link attributes.  There
   are several advantages in using Extended Link LSA:

   1.  Advertisement of the link attributes does not make the link part
       of the TE topology.  It avoids any conflicts and is fully
       compatible with the [RFC3630].

   2.  The TE Opaque LSA remains truly opaque to OSPFv2 as originally
       defined in [RFC3630].  Its content is not inspected by OSPFv2 and
       OSPFv2 acts as a pure transport.





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   3.  There is clear distinction between link attributes used by TE and
       link attributes used by other OSPFv2 applications.

   4.  All link attributes that are used by OSPFv2 applications are
       advertised in a single LSA, the Extended Link Opaque LSA.

   The disadvantage of this approach is that in rare cases, the same
   link attribute is advertised in both the TE Opaque and Extended Link
   Attribute LSAs.  Additionally, there will be additional
   standardization effort.  However, this could also be viewed as an
   advantage as the non-TE use cases for the TE link attributes are
   documented and validated by the OSPF working group.

3.3.  Proposed solution

   It is RECOMMENDED to use the Extended Link Opaque LSA
   ([I-D.ietf-ospf-prefix-link-attr] to advertise any link attributes
   used for non-TE purposes in OSPFv2, including those that have been
   originally defined for TE purposes.  TE link attributes used for TE
   purposes continue to use TE Opaque LSA ([RFC3630]).

   Is is also RECOMMENDED to keep the format of the link attribute TLVs
   that have been defined for TE purposes unchanged even when they are
   used for non-TE purposes.

   Finally, it is RECOMMENDED to allocate unique code points for link
   attribute TLVs that have been defined for TE purposes for the OSPFv2
   Extended Link TLV Sub-TLV Registry as defined in
   [I-D.ietf-ospf-prefix-link-attr].  For each reused TLV, the code
   point will be defined in an IETF document along with the expected
   usecase(s).

4.  Reused TE link attributes

   This section defines the use case and code points for the OSPFv2
   Extended Link TLV Sub-TLV Registry for some of the link attributes
   that have been originally defined for TE or GMPLS purposes.

4.1.  Remote interface IP address

   The OSPFv2 description of an IP numbered point-to-point adjacency
   does not include remote IP address.  As described in Section 2, this
   makes the two-way connectivity check ambiguous in the presence of the
   parallel point-to-point links between two OSPFv2 routers.

   The Remote IP address of the link can also be used for Segment
   Routing traffic engineering to identify the link in a set of parallel
   links between two OSPFv2 routers



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   [I-D.ietf-ospf-segment-routing-extensions].  Similarly, the remote IP
   address is useful in identifying individual parallel OSPF links
   advertised in BGP Link-State as described in
   [I-D.ietf-idr-ls-distribution].

   To advertise the Remote interface IP address in the OSPFv2 Extended
   Link TLV, the same format of the sub-TLV as defined in section 2.5.4.
   of [RFC3630] is used and TLV type 4 is used.

4.2.  Link Local/Remote Identifiers

   The OSPFv2 description of an IP unnumbered point-to-point adjacency
   does not include remote link identifier.  As described in Section 2,
   this makes the two-way connectivity check ambiguous in the presence
   of the parallel point-to-point IP unnumbered links between two OSPFv2
   routers.

   The local and remote link identifiers can also be used for Segment
   Routing traffic engineering to identify the link in a set of parallel
   IP unnumbered links between two OSPFv2 routers
   [I-D.ietf-ospf-segment-routing-extensions].  Similarly, these
   identifiers are useful in identifying individual parallel OSPF links
   advertised in BGP Link-State as described in
   [I-D.ietf-idr-ls-distribution].

   To advertise the link Local/Remote identifiers in the OSPFv2 Extended
   Link TLV, the same format of the sub-TLV as defined in section 1.1.
   of [RFC4203] is used and TLV type 5 is used.

4.3.  Shared Risk Link Group (SRLG)

   The SRLG of a link can be used in IPFRR to compute a backup path that
   does not share any SRLG group with the protected link.

   To advertise the SRLG of the link in the OSPFv2 Extended Link TLV,
   the same format of the sub-TLV as defined in section 1.3. of
   [RFC4203] is used and TLV type 6 is used.

4.4.  Extended Metrics

   [RFC3630] defines several link bandwidth types.  [RFC7471] defines
   extended link metrics that are based on link bandwidth, delay and
   loss characteristics.  All these can be used to compute best paths
   within an OSPF area to satisfy requirements for bandwidth, delay
   (nominal or worst case) or loss.






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   To advertise extended link metrics in the OSPFv2 Extended Link TLV,
   the same format of the sub-TLVs as defined in [RFC7471] is used with
   following TLV types:

      7 - Unidirectional Link Delay

      8 - Min/Max Unidirectional Link Delay

      9 - Unidirectional Delay Variation

      10 - Unidirectional Link Loss

      11 - Unidirectional Residual Bandwidth

      12 - Unidirectional Available Bandwidth

      13 - Unidirectional Utilized Bandwidth

   To advertise link maximum bandwidth, maximum reservable bandwidth an
   unreserved bandwidth in the OSPFv2 Extended Link TLV, the same format
   of the sub-TLVs as defined in [RFC3630] is used with following TLV
   types:

      7 - Maximum bandwidth

      8 - Maximum reservable bandwidth

      9 - Unreserved bandwidth

5.  Backward Compatibility

   If the same link attribute is advertised in both TE Opaque LSA
   [RFC3630] and in Extended Link Opaque LSA
   [I-D.ietf-ospf-prefix-link-attr] it is expected that the information
   would be identical.  If they are different, TE will use the
   information in the TE Opaque LSA [RFC3630] and the non-TE
   applications will use the information in the OSPFv2 Extended Link
   Opaque LSA [I-D.ietf-ospf-prefix-link-attr].

6.  Security Considerations

   Implementations must assure that malformed TLV and Sub-TLV
   permutations do not result in errors that cause hard OSPFv2 failures.








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7.  IANA Considerations

   This specification updates the OSPFv2 Extended Link TLV sub-TLV
   registry that is defined in [I-D.ietf-ospf-prefix-link-attr] with the
   following TLV types:

      4 - Remote interface IP address

      5 - Link Local/Remote Identifiers

      6 - Shared Risk Link Group

      7 - Unidirectional Link Delay

      8 - Min/Max Unidirectional Link Delay

      9 - Unidirectional Delay Variation

      10 - Unidirectional Link Loss

      11 - Unidirectional Residual Bandwidth

      12 - Unidirectional Available Bandwidth

      13 - Unidirectional Utilized Bandwidth

8.  Acknowledgments

9.  References

9.1.  Normative References

   [I-D.ietf-idr-ls-distribution]
              Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
              Ray, "North-Bound Distribution of Link-State and TE
              Information using BGP", draft-ietf-idr-ls-distribution-11
              (work in progress), June 2015.

   [I-D.ietf-ospf-prefix-link-attr]
              Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", draft-ietf-ospf-prefix-link-attr-06 (work
              in progress), June 2015.








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   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-05 (work in progress), June 2015.

   [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>.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
              July 2008, <http://www.rfc-editor.org/info/rfc5250>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <http://www.rfc-editor.org/info/rfc5714>.

9.2.  Informative References

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <http://www.rfc-editor.org/info/rfc4203>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <http://www.rfc-editor.org/info/rfc7471>.

Authors' Addresses










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   Peter Psenak
   Cisco Systems
   Apollo Business Center
   Mlynske nivy 43
   Bratislava, 821 09
   Slovakia

   Email: ppsenak@cisco.com


   Acee Lindem
   Cisco Systems
   301 Midenhall Way
   Cary, NC  27513
   USA

   Email: acee@cisco.com


   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan
   Antwerp, 2018  94089
   Belgium

   Email: wim.henderickx@alcatel-lucent.com


   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose, CA  95134
   USA

   Email: jeff.tantsura@ericsson.com


   Hannes Gredler
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   USA

   Email: hannes@juniper.net







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