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Versions: (draft-keyupate-ospf-ospfv2-hbit) 00 01 02 03

OSPF                                                            K. Patel
Internet-Draft                                                    Arrcus
Intended status: Standards Track                       P. Pillay-Esnault
Expires: December 16, 2017                           Huawei Technologies
                                                             M. Bhardwaj
                                                            S. Bayraktar
                                                           Cisco Systems
                                                           June 14, 2017


                        H-bit Support for OSPFv2
                     draft-ietf-ospf-ospfv2-hbit-03

Abstract

   OSPFv3 defines an option field for router-LSAs known as a R-bit in
   RFC5340.  If the R-bit is clear, an OSPFv3 router can participate in
   OSPF topology distribution without acting as a forwarder to forward
   the transit traffic.  In such cases, an OSPF router would only accept
   traffic intended for local delivery.  This draft defines R-bit
   functionality for OSPFv2 defined in RFC2328.

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
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   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 December 16, 2017.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  H-bit Support . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  SPF Modifications . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Auto Discovery and Backwards Compatibility  . . . . . . . . .   5
   6.  OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     11.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   OSPFv3 [RFC5340] defines an option field for router-LSAs known as a
   R-bit.  If the R-bit is clear, an OSPF router can participate in
   OSPFv3 topology distribution without acting as a forwarder to forward
   the transit traffic.  In such cases, an OSPF router would only accept
   traffic intended for local delivery.

   This functionality is particularly useful for BGP Route Reflectors
   known as virtual Route Reflectors (vRRs) that are not in the
   forwarding path but are in central location such as data centers.
   Such Route Reflectors typically are used for route distribution and
   are not capable of forwarding data traffic.  However, they need to
   participate in the IGP routing for: 1) computing SPFs for Optimal
   Route Reflection functionality defined in
   [I-D.ietf-idr-bgp-optimal-route-reflection], and 2) resolving
   reachability for its Route Reflector Clients.

   This draft defines R-bit functionality for OSPFv2 defined in
   [RFC2328] by introducing a new Router LSA bit known as a "H-bit".








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2.  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] only when
   they appear in all upper case.  They may also appear in lower or
   mixed case as English words, without any normative meaning.

3.  H-bit Support

   This draft defines a new Router-LSA bit known as a Host Bit or a
   H-bit.  The H-bit indicates the OSPFv2's capability of acting as a
   transit router.  When set, the OSPFv2 router indicates that the
   transit capability is disabled.  The bit value usage of the H-bit is
   reversed as opposed to the R-bit value defined in OSPFv3 [RFC5340] to
   support backward compatibility.  The OSPFv2 Router LSA format is
   defined as:


































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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            LS age             |     Options   |       1       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Link State ID                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Advertising Router                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     LS sequence number                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         LS checksum           |             length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |H|0|0|N|W|V|E|B|        0      |            # links            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Link ID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Link Data                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     # TOS     |            metric             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      TOS      |        0      |          TOS  metric          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Link ID                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Link Data                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |

      bit H
          When set, an OSPFv2 router is a non-transit router and is
          incapable of acting as a forwarder.


   When H-bit is set, an OSPFv2 router is a non-transit router and is
   incapable of acting as a forwarder.  In this mode, the other OSPFv2
   routers SHOULD NOT use the originating OSPFv2 router for the transit
   traffic, but they will use the OSPFv2 router for data traffic
   destined to that OSPFv2 router.  An OSPFv2 router originating a
   Router LSA with the H-bit set SHOULD advertise its LINKS with MAX
   Link cost as defined in Section 3 of [RFC6987].  This is to increase
   the applicability of the H-bit in partial deployments where it is the
   responsibility of the operator to ensure that the H-bit does not
   result in routing loops.





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   When H-bit is set, IPv4 prefixes associated with local interfaces MAY
   be advertised in summary LSAs.  Non-local IPv4 prefixes, e.g., those
   advertised by other routers and installed during the SPF computation,
   MAY be advertised in summary-LSAs if configured by policy.  Likewise,
   when H-bit is set, only IPv4 prefixes associated with local
   interfaces MAY be advertised in AS-external LSAs.  Non-local IPv4
   prefixes, e.g., those exported from other routing protocols, MUST NOT
   be advertised in AS-external-LSAs.  Finally, when H-bit is set, an
   ABR MUST advertise a consistent H-bit setting in its self-originated
   router-LSAs for all attached areas.

4.  SPF Modifications

   The SPF calculation described in section 16.1 [RFC2328] will be
   modified to assure that the routers originating router-LSAs with the
   H-bit set will not be used for transit traffic.  Step 2 is modified
   as follows:


                2) Call the vertex just added to the
                   tree vertex V.  Examine the LSA
                   associated with vertex V.  This is
                   a lookup in the Area A's link state
                   database based on the Vertex ID. If
                   this is a router-LSA, and the H-bit
                   of the router-LSA is set, and
                   vertex V is not the root, then the
                   router should not be used for transit
                   and step (3) should be executed
                   immediately. If this is a router-LSA,
                   and bit V of the router-LSA (see
                   Section A.4.2) is set, set Area A's
                   TransitCapability to TRUE. In any case,
                   each link described by the LSA gives
                   the cost to an adjacent vertex.  For
                   each described link, (say it joins
                   vertex V to vertex W):


5.  Auto Discovery and Backwards Compatibility

   To avoid the possibility of any routing loops due to partial
   deployments, this draft defines a new OSPF Router Functional
   Capability known as a Host Support Capability.  The value of this
   capability is a bit value to be assigned by IANA from OSPF Router
   Functional Capability Bits registry [RFC7770] .





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   The Auto Discovery via announcement of the Host Support Functional
   Capability ensures that the H-bit functionality and its associated
   SPF changes SHOULD only take effect if all the routers in a given
   OSPF area support this functionality.

   Implementations are encouraged to provide a knob to manually override
   enforcement of the H-bit functionality in partial deployment
   scenarios for cases where the topology guarantees that the router
   supporting the H-bit will not cause routing loops.

6.  OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics

   When calculating the path to an OSPF AS-External-LSA or NSSA-LSA with
   a Type-2 metric, the advertised Type-2 metric is taken as more
   significant than the OSPF intra-area or inter-area path.  Hence,
   advertising the links with MaxLinkMetric as specified in [RFC6987]
   does not discourage transit traffic when calculating AS external or
   NSSA routes.  Consequently, OSPF routers implementing [RFC6987] or
   this specification should advertise a Type-2 metric of LSInfinity for
   any self-originated AS-External-LSAs or NSSA-LSAs in situations when
   the OSPF router is acting as a stub router [RFC6987] or implementing
   this specification.

7.  IANA Considerations

   This draft defines a new Router LSA bit known as a H-bit.  This draft
   requests IANA to 1) Create a new OSPF Router LSA bits registry and 2)
   assign a H-bit code type from the newly allocated OSPF Router LSA bit
   registry.

   This draft defines a new Router Functional Capability known as a Host
   Support Functional Capability.  This draft requests IANA to allocate
   the value of this capability from the Router Functional Capability
   Bits TLV.

8.  Security Considerations

   This document introduces no new security considerations above and
   beyond those already specified in [RFC2328] and [RFC5340].

9.  Acknowledgements

   The authors would like to acknowledge Hasmit Grover for discovery of
   the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward,
   Burjiz Pithawala and Michael Barnes for their comments.






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10.  Change Log

   Initial Version:  April 23 2015

11.  References

11.1.  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>.

   [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>.

   [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>.

11.2.  Informative References

   [I-D.ietf-idr-bgp-optimal-route-reflection]
              Raszuk, R., Cassar, C., Aman, E., Decraene, B., Litkowski,
              S., and K. Wang, "BGP Optimal Route Reflection (BGP-ORR)",
              draft-ietf-idr-bgp-optimal-route-reflection-13 (work in
              progress), January 2017.

   [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>.

Authors' Addresses

   Keyur Patel
   Arrcus

   Email: keyur@arrcus.com






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   Padma Pillay-Esnault
   Huawei Technologies
   2330 Central Expressway
   Santa Clara,  CA 95050
   USA

   Email: padma@huawei.com


   Manish Bhardwaj
   Cisco Systems
   170 W. Tasman Drive
   San Jose,  CA 95134
   USA

   Email: manbhard@cisco.com


   Serpil Bayraktar
   Cisco Systems
   170 W. Tasman Drive
   San Jose,  CA 95134
   USA

   Email: serpil@cisco.com


























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