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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 5838

Network Working Group                                 A. Lindem (Editor)
Internet-Draft                                              S. Mirtorabi
Expires: March 5, 2006                                            A. Roy
                                                               M. Barnes
                                                           Cisco Systems
                                                                Q. Vohra
                                                        Juniper Networks
                                                          September 2005


                 Support of address families in OSPFv3
                     draft-ietf-ospf-af-alt-02.txt

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   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on March 5, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes a mechanism for supporting multiple address
   families in OSPFv3 using multiple instances.  It maps an address
   family (AF) to an OSPFv3 instance using the Instance ID field in the
   OSPFv3 packet header.  This approach is fairly simple and minimizes



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   extensions to OSPFv3 for supporting multiple AF's.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Design Considerations  . . . . . . . . . . . . . . . . . .  3
     1.2   Requirements notation  . . . . . . . . . . . . . . . . . .  3
   2.  Proposed Solution  . . . . . . . . . . . . . . . . . . . . . .  4
     2.1   Instance ID values for new AF's  . . . . . . . . . . . . .  4
     2.2   OSPFv3 Options and Prefix Options Chnages  . . . . . . . .  4
       2.2.1   OSPFv3 Options . . . . . . . . . . . . . . . . . . . .  4
       2.2.2   Prefix Options . . . . . . . . . . . . . . . . . . . .  5
     2.3   Advertising Prefixes in new AF's . . . . . . . . . . . . .  5
     2.4   Changes to the Hello processing  . . . . . . . . . . . . .  5
     2.5   Next hop for IPv4 unicast and multicast AF's . . . . . . .  6
     2.6   Operation over Virtual Links . . . . . . . . . . . . . . .  6
   3.  Backward Compatibility . . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
   A.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
       Intellectual Property and Copyright Statements . . . . . . . . 13




























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1.  Introduction

   OSPFv3 has been defined to support IPv6 unicast AF.  There is a need
   to carry other AFs in OSPFv3 such as multicast IPv6, unicast or
   multicast IPv4.  This document introduces these other AFs in OSPFv3
   by reserving Instance IDs and using one OSPFv3 instance for one AF.

1.1  Design Considerations

   This section describes the rationale for adopting the multiple
   instance ID approach for supporting multiple address families in
   OSPFv3.  As described earlier, OSPFv3 is designed to support multiple
   instances.  Hence mapping an instance to an address family doesn't
   introduce new mechanisms in the protocol.  It minimizes the protocol
   extensions required and it simplifies the implementation.  The
   presence of a separate link state database per address family is also
   easier to debug and operate.  Additionally, it doesn't change the
   existing instance, area and interface based configuration model in
   most OSPF implementations.

1.2  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 [RFC2119].


























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2.  Proposed Solution

   Currently the entire Instance ID number space is used for IPv6
   unicast.  We propose to assign different ranges to different AF's in
   order to support other AF's in OSPFv3.  Each AF will establish
   different adjacency, have different link state database and compute
   different shortest path tree.  Additionally, the current LSAs that
   are defined to carry IPv6 unicast prefix can be used without any
   modification in different instances to carry different AF's prefixes.

   It should be noted that OSPFv3 is running on the top of IPv6 and uses
   IPv6 link local address for OSPFv3 control packet and next hop
   calculation.  Therefore, it is required that IPv6 be enabled on a
   link, although the link may not be participating in IPv6 unicast AF.

2.1  Instance ID values for new AF's

   Instance ID zero is already used by default for IPv6 unicast AF.  We
   define the following ranges for different AF's.  The first value of
   each range is considered as the default value for the corresponding
   AF.

      Instance ID # 0    -  # 31     IPv6 unicast AF
      Instance ID # 32   -  # 63     IPv6 multicast AF
      Instance ID # 64   -  # 95     IPv4 unicast AF
      Instance ID # 96   -  # 127    IPv4 multicast AF
      Instance ID # 128  -  # 255    Reserved


2.2  OSPFv3 Options and Prefix Options Chnages

   A new bit is added to the OSPFv3 options field and a couple of the
   bits are only applicable to the IPv6 unicast AF.

2.2.1  OSPFv3 Options



                               1                     2
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8  9  0  1  2  3
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+--+--+--+
          | | | | | | | | | | | | | | | |AF|*|*|DC|R|N|MC| E|V6|
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+--+--+--+

                           The Options field






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   V6-bit
      The V6 bit is used in OSPFv3 to exclude a node from IPv6 unicast
      route calculation but allow it in the SPF calculation for other
      address families.  Since Instance ID now denotes the AF
      explicitly, this bit is ignored in AF's other than IPv6 unicast.

   MC-bit
      This bit is not used in other AF's introduced in this document.

   AF-bit
      When a router supports AF, it MUST set this new bit in the Options
      field of Hello Packets, DD packets and LSAs.


2.2.2  Prefix Options


                0  1  2  3  4  5  6  7
               +--+--+--+--+--+--+--+--+
               |  |  |  |  | P|* |LA|NU|
               +--+--+--+--+--+--+--+--+



   MC-bit
      This bit is not used in other AF's introduced in this document.

   NU-bit
      The NU bit must be clear in all unicast AF's and it must be set in
      all multicast AF's.

   Note that all bits unused in a given AF could be redefined later.

2.3  Advertising Prefixes in new AF's

   Each Prefix defined in OSPFv3 has a prefix length field.  This
   facilitate advertising prefixes of different lengths in different
   AF's.  The existing LSAs defined in OSPFv3 are used for this purpose
   and there is no need to define new LSAs.

2.4  Changes to the Hello processing

   When a router does not support an AF but it is configured with an
   Instance ID in the same range, packets could be blackholed.  This
   could happen due to misconfiguration or router downgrade to a
   previous code level.  Blackholing is possible because the router
   which doesn't support the AF can still be included in the SPF
   calculated path as long as it establishes adjacencies using the



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   Instance ID corresponding to the AF.  Note that router and network
   LSAs are AF independent.

   In order to avoid the above situation, hello processing is changed in
   order to only establish adjacency with the routers that have the AF-
   bit set in their Options field.

   Receiving Hello Packets is specified in section 3.2.2.1 of [OSPFV3].
   The following check is added to Hello reception:


   o  When a router participate in an AF (sets the AF-bit in Options
      field) it MUST discard Hello packets having the AF-bit clear in
      the Options field.  The only exception is IPv6 unicast AF, where
      this check MUST NOT be done (to help backward compatibility).


2.5  Next hop for IPv4 unicast and multicast AF's

   OSPFv3 runs on the top of IPv6 and uses IPv6 link local addresses for
   OSPFv3 control packets and next hop calculations.  Although IPV6 link
   local addresses could be used as next hops for IPv4 address families,
   it is desirable to have IPv4 next hop addresses.  For example, in
   IPv4 multicast having the nexthop address the same as the PIM
   neighbor address (IPv4 address) makes it easier to know to which
   upstream neighbor to send a PIM join when doing a RPF lookup for a
   source.  It is also easier for troubleshooting purposes to have a
   next hop with the same semantics as the AF.

   In order to achieve this, the link's IPv4 address will be advertised
   in the "link local address" field of the IPv4 instance's Link-LSA.
   This address is placed in the first 32 bit of "link local address"
   field and used for IPv4 next hop calculations.

   We call direct interface address (DIA) the address that is reachable
   directly via the link provided that a layer 3 to layer 2 mapping is
   available.  Note that there is no explicit need for the IPv4 link
   addresses to be on the same subnet.  An implementation should resolve
   layer 3 to layer 2 mappings via ARP or ND for a DIA even if the IPv4
   address is not on the same subnet as the router's interface IP
   address.

2.6  Operation over Virtual Links

   OSPFv3 control packets sent over a virtual link are IPv6 packets and
   may traverse multiples hops.  Therefore, there must be a global IPv6
   address associated with the virtual link so that the control packet
   is forwarded correctly by the intermediate hops between VL end



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   points.  Although this requirement can be satisfied in IPv6 unicast
   AF, this will not function in other AFs as there cannot be a multihop
   forwarding based on global IPv6 address or such a path may not exist.
   Therefore virtual link are not currently supported in other AF's.















































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3.  Backward Compatibility

   Each new AF will have their corresponding Instance ID and can operate
   with the existing non-capable routers in IPv6 unicast topology.
   Further, when a non-capable router uses an Instance ID which is
   reserved for a given AF, since the non-capable router will not have
   the AF-bit set in the Hello an adjacency will not be established with
   an AF capable router.  Therefore, there are no backward compatibility
   issues.  AF's can be gradually deployed without disturbing networks
   with current non-capable routers.









































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4.  Security Considerations

   The function described in this document does not create any new
   security issues for the OSPF protocol.  Security considerations for
   the OSPFv are covered in [OSPFV3].














































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5.  IANA Considerations

   The following IANA assignments are to be made from existing
   registries:

   o  An OSPFv3 options bit will be allocated for support of address
      families using separate instances.


6.  Normative References

   [OSPFV3]   Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
              RFC 2740, December 1999.

   [RFC2119]  Bradner, S., "Key words for use in RFC's to Indicate
              Requirement Levels", RFC 2119, March 1997.


Authors' Addresses

   Acee Lindem
   Cisco Systems
   7025 Kit Creek Road
   Research Triangle Park, NC  27709
   USA

   Email: acee@cisco.com


   Sina Mirtorabi
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: sina@cisco.com


   Abhay Roy
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: akr@cisco.com






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   Michael Barnes
   Cisco Systems
   225 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: mjbarnes@cisco.com


   Quaizar Vohra
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   USA

   Email: qv@juniper.net



































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Appendix A.  Acknowledgments

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
















































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