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Versions: (draft-keyupate-ospf-ospfv2-hbit) 00 01 02 03 04 05 06 07

OSPF                                                            K. Patel
Internet-Draft                                                    Arrcus
Updates: 2328 (if approved)                            P. Pillay-Esnault
Intended status: Standards Track                     Huawei Technologies
Expires: November 20, 2019                                   M. Bhardwaj
                                                            S. Bayraktar
                                                           Cisco Systems
                                                            May 19, 2019


                     Host Router Support for OSPFv2
                     draft-ietf-ospf-ospfv2-hbit-07

Abstract

   The OSPFv2 specifies an SPF algorithm that identifies transit
   vertices based on their adjacencies.  Therefore, OSPFv2 does not have
   a mechanism to prevent traffic transiting a participating node if it
   is a transit vertex in the only existing or shortest path to the
   destination.  The use of metrics to make the node undesirable can
   only help to repel traffic if an alternative better route exists.
   This document defines the Host-bit functionality to prevent other
   OSPFv2 routers from using the router for transit traffic in OSPFv2
   routing domains.  This document updates the [RFC2328] by assigning a
   new bit (Host-bit) in the OSPF Router-LSA bit registry.  If the Host-
   bit is set, the calculation of the shortest-path tree for an area, as
   described in [RFC2328], is modified by including a new check to
   verify that transit vertices have the Host-bit clear.

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
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   Drafts is at https://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 November 20, 2019.






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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Host-bit Support  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  SPF Modifications . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Auto Discovery and Backward Compatibility . . . . . . . . . .   6
   6.  OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The OSPFv2 specifies an SPF algorithm that identifies transit
   vertices based on their adjacencies.  Therefore, OSPFv2 does not have
   a mechanism to prevent traffic transiting a participating node if it



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   is a transit vertex in the only existing or shortest path to the
   destination.  The use of metrics to make the node undesirable can
   only help to repel traffic if an alternative better route exists.

   This functionality is particularly useful for a number of use cases:

   1.  To isolate a router to avoid blackhole scenarios when there is a
       reload and possible long reconvergence times.

   2.  Closet Switches are usually not used for transit traffic but need
       to participate in the topology.

   3.  Overloaded routers could use such a capability to repel traffic
       until they stabilize.

   4.  BGP Route reflectors known as virtual Route Reflectors (vRRs),
       that are not in the forwarding path but are in central locations
       such as data centers.  Such Route Reflectors typically are used
       for route distribution and are not capable of forwarding transit
       traffic.  However, they need to learn the OSPF topology to
       perform spf computation for optimal routes and reachbility
       resolution for its clients
       [I-D.ietf-idr-bgp-optimal-route-reflection].

   This document defines the Host-bit (H-Bit)functionality to prevent
   other OSPFv2 routers from using the router for transit traffic in
   OSPFv2 routing domains.  This document updates the [RFC2328] by -
   assigning the Host-bit in the OSPF Router-LSA bit registry - if the
   host-bit is set then the calculation of the shortest-path tree for an
   area, as described in section 16.1 of [RFC2328], is modified by
   including a new check to verify that transit vertices DO NOT have the
   host-bit set.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Host-bit Support

   This document defines a new router-LSA bit known as the Host Bit or
   the H-bit.  An OSPFv2 router advertising a router-LSA with the H-bit
   set indicates to other OSPFv2 routers in the area supporting the
   functionality that it MUST NOT be used as a transit router (see
   section 4).



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   If the host-bit is NOT set routers MUST act transit routers as
   described in [RFC2328] ensuring backward compatibility.


        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                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |


                          Host Bit in router-LSA

                 0 1 2 3 4 5 6 7
                 +-+-+-+-+-+-+-+-+
                 |H|0|0|N|W|V|E|B|
                 +-+-+-+-+-+-+-+-+

                                 Host Bit

   Bit H is the high-order bit of the OSPF as shown above.  When set, an
   OSPFv2 router is a non-transit router and is incapable of forwarding
   transit traffic.



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   An OSPFv2 router originating a router-LSA with the H-bit set MUST
   advertise all its router links with a link cost of MaxLinkMetric
   [RFC6987].  This is to increase the applicability of the H-bit to
   partial deployments where it is the responsibility of the operator to
   ensure that OSPFv2 routers not supporting the H-bit do not install
   routes causing routing loops.

   When the H-bit is set, an Area Border Router (ABR) MUST advertise a
   consistent H-bit setting in its self-originated router-LSAs for all
   attached areas.  ONLY IPv4 prefixes associated with its local
   interfaces MAY be advertised in summary LSAs.

   When the H-bit is set cannot act as an AS Boundary Router (ASBR), as
   non-local IPv4 prefixes, e.g., those exported from other routing
   protocols, MUST NOT be advertised in AS-external-LSAs.

4.  SPF Modifications

   The SPF calculation described in section 16.1 [RFC2328] will be
   modified to ensure 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):









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5.  Auto Discovery and Backward Compatibility

   To avoid the possibility of any routing loops due to partial
   deployment, this document defines a OSPF Router Information (RI) LSA
   with a Router Functional Capability TLV that includes the following
   Router Functional Capability Bit:

                  Bit       Capabilities

                  7         Host Router Support capability

   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 configuration parameter
   to manually override enforcement of the H-bit functionality in
   partial deployments where the topology guarantees that OSPFv2 routers
   not supporting the H-bit do not compute routes resulting in routing
   loops.  More precisely, the advertisement of MaxLinkMetric for the
   router's non-local links will prevent OSPFv2 routers not supporting
   the H-bit from attempting to use it for transit traffic.

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

   IANA is requested to create the OSPF Router-LSA bit registry with the
   following assignments:










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        Value   Description                                 Reference
        0x01    Area Border Router (B-bit)                  [RFC2328]
        0x02    AS Boundary Router (E-bit)                  [RFC2328]
        0x04    Virtual Link Endpoint (V-bit)               [RFC2328]
        0x08    Historic (W-bit)                            [RFC1584]
        0x10    Unconditional NSSA Translator (Nt-bit)      [RFC3101]
        0x20    Unassigned
        0x40    Unassigned
        0x80    Host (H-bit)                            This Document


   This document also defines a new Router Functional Capability
   [RFC7770] known as the Host Router Support Functional Capability.
   This document 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 beyond those
   already specified in [RFC6987], [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.

10.  References

10.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RFC3101]  Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
              RFC 3101, DOI 10.17487/RFC3101, January 2003,
              <https://www.rfc-editor.org/info/rfc3101>.

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




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   [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, <https://www.rfc-editor.org/info/rfc7770>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [I-D.ietf-idr-bgp-optimal-route-reflection]
              Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K.
              Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft-
              ietf-idr-bgp-optimal-route-reflection-18 (work in
              progress), April 2019.

   [RFC1584]  Moy, J., "Multicast Extensions to OSPF", RFC 1584,
              DOI 10.17487/RFC1584, March 1994,
              <https://www.rfc-editor.org/info/rfc1584>.

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

Authors' Addresses

   Keyur Patel
   Arrcus

   Email: keyur@arrcus.com


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

   Email: padma@huawei.com










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   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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