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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                                          Redback Networks
Intended status: Standards Track                            S. Mirtorabi
Expires: January 2, 2010                                          A. Roy
                                                               M. Barnes
                                                           Cisco Systems
                                                             R. Aggarwal
                                                        Juniper Networks
                                                             Jul 11 2009


                 Support of address families in OSPFv3
                     draft-ietf-ospf-af-alt-08.txt

Status of this Memo

   This Internet-Draft is submitted to IETF 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 2, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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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
   extensions to OSPFv3 for supporting multiple AFs.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Design Considerations  . . . . . . . . . . . . . . . . . .  3
     1.2.  Requirements notation  . . . . . . . . . . . . . . . . . .  3
   2.  Protocol Details . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Instance ID values for new AFs . . . . . . . . . . . . . .  4
     2.2.  OSPFv3 Options Changes . . . . . . . . . . . . . . . . . .  4
     2.3.  Advertising Prefixes in new AFs  . . . . . . . . . . . . .  5
     2.4.  Changes to the Hello processing  . . . . . . . . . . . . .  5
     2.5.  Next hop for IPv4 unicast and multicast AFs  . . . . . . .  5
     2.6.  AS External LSA Forwarding Address for IPv4 Unicast
           and IPv4 Multicast AFs . . . . . . . . . . . . . . . . . .  6
     2.7.  Database Description Maximum Transmissoin Unit (MTU)
           Specification for Non-IPv6 AFs . . . . . . . . . . . . . .  6
     2.8.  Operation over Virtual Links . . . . . . . . . . . . . . .  9
   3.  Backward Compatibility . . . . . . . . . . . . . . . . . . . . 10
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16


















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1.  Introduction

   OSPFv3 [OSPFV3] has been defined to support the base IPv6 unicast
   Address Family (AF).  There are requirements to advertise other AFs
   in OSPFv3 including multicast IPv6, unicast IPv4, and multicast IPv4.
   This document supports these other AFs in OSPFv3 by mapping each AF
   to a separate Instance ID and OSPFv3 instance.

1.1.  Design Considerations

   This section describes the rationale for using the multiple instance
   ID approach to support 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 any
   new mechanisms to 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
   OSPFv3 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 [RFC-KEYWORDS].

























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2.  Protocol Details

   Currently the entire Instance ID number space is used for IPv6
   unicast.  This specification assigns different Instance ID ranges to
   different AFs in order to support other AFs in OSPFv3.  Each Instance
   ID implies a separate OSPFv3 instance with its own neighbor
   adjacencies, link state database, protocol data structures, and
   shortest path first (SPF) computation.

   Additionally, the current LSAs that are defined to advertise IPv6
   unicast prefixes can be used without any modifications to advertise
   prefixes from other AFs.

   It should be noted that OSPFv3 is running on top of IPv6 and uses
   IPv6 link local addresses for OSPFv3 control packets.  Therefore, it
   is required that IPv6 be enabled on a link, although the link may not
   be participating in any IPv6 AF.

2.1.  Instance ID values for new AFs

   Instance ID zero is already defined by default for the IPv6 unicast
   AF.  We define the following ranges for different AFs.  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    Unassigned

                            OSPFv3 Instance IDs

2.2.  OSPFv3 Options Changes

   A new AF-bit is added to the OSPFv3 options field.  V6-bit and MC-bit
   are only applicable to the IPv6 unicast AF.


                               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|x | E|V6|
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+-+-+--+--+--+

                           The Options field

                              OSPFv3 Options



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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 AFs other than IPv6 unicast.

   AF-bit
      When a router supports AF, it MUST set this new bit in the OSPFv3
      Options field of Hello Packets, DD packets, and LSAs.

2.3.  Advertising Prefixes in new AFs

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

   Prefixes which don't match the AF of the OSPFv3 instance, MUST be
   discarded in any route computation.

2.4.  Changes to the Hello processing

   When a router does not support an AF but it is configured with the
   corresponding Instance ID packets could be black holed.  This could
   happen due to misconfiguration or a router software downgrade.  Black
   holing 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 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 adjacencies with 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 participates 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 the Base IPv6 unicast
      AF, where this check MUST NOT be done (for backward
      compatibility).

2.5.  Next hop for IPv4 unicast and multicast AFs

   OSPFv3 runs on 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,



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   it is desirable to have IPv4 next hop addresses.  For example, in
   IPv4 multicast having the next hop address the same as the Protocol
   Independent Multicast (PIM) [PIM] neighbor address (IPv4 address)
   makes it easier to determine which upstream neighbor to send a PIM
   join when doing a Reverse Path Forwarding (RPF) lookup.  It is also
   easier for troubleshooting to have a next hop with the same 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.  The remaining bits
   MUST be set to zero.

   We call the 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 Address Resolution
   Protocol (ARP) [ARP] or Neighbor Discovery (ND) [ND] for a DIA even
   if the IPv4 address is not on the same subnet as the router's
   interface IP address.

2.6.  AS External LSA Forwarding Address for IPv4 Unicast and IPv4
      Multicast AFs

   For OSPFv3, this address is an IPv6 host address (128 bits).  If
   included, data traffic for the advertised destination will be
   forwarded to this address.  For IPv4 unicast and IPv4 multicast AFs,
   the Forwarding Address in AS-external-LSAs MUST encode an IPv4
   address.  To achieve this, the IPv4 Forwarding Address is advertised
   by placing it in the first 32 bits of the Forwarding Address field in
   the AS-external-LSAs.  The remaining bits MUST be set to zero.

2.7.  Database Description Maximum Transmissoin Unit (MTU)
      Specification for Non-IPv6 AFs

   For address families other than IPv6, both the MTU for the address
   family of the instance and IPv6 MTU used for OSPFv3 maximum packet
   determination MUST be considered.  The MTU in the Database
   Description packet MUST always contain the MTU corresponding to the
   advertised address family.  For example, if the instance corresponds
   to an IPv4 address family, the IPv4 MTU for the interface MUST be
   specified in the interface MTU field.  As specified section 10.6 of
   [OSPFV2], the Database Description packet will be rejected if the MTU
   is greater than the receiving interface's MTU for the address family
   corresponding to the instance.  This behavior will assure an
   adjacency is not formed and address family specific routes are not
   installed over a path with conflicting MTUs.



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   The value used for OSPFv3 maximum packet size determination MUST also
   be compatible for an adjacency to be established.  Since only a
   single MTU field is specified, the M6-bit is defined by this
   specification.  If the M6-bit is clear, the specified MTU SHOULD also
   be checked against the IPv6 MTU and the Database Description packet
   SHOULD be rejected if the MTU is larger than the receiving
   interface's IPv6 MTU.  An OSPFv3 router SHOULD NOT set the M6-bit if
   its IPv6 MTU and address family specific MTU are the same.

   If the IPv6 and IPv4 MTUs differ, the M6-bit MUST be set for non-IPv6
   address families.  If the M6-bit is set, the IPv6 MTU is decided by
   the presence or absense of IPv6 MTU TLV in the LLS [LLS] block.  If
   this TLV is present, it carries the IPv6 MTU which SHOULD be compared
   with local IPv6 MTU.  If this TLV is absent, the minimum IPv6 MTU of
   1280 octets SHOULD be used for the comparison (refer to [IPV6]).

   If the M6-bit is set in a received Database Description packet for a
   non-IPv6 address family, the receiving router MUST NOT check the
   Interface MTU in the Database Exchange packet against the receiving
   interface's IPv6 MTU.

   The figure below graphically depicts the OSPFv3 Database Description
   Packet:




























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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |      3        |       2       |        Packet Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |                           Router ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |                             Area ID                             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |           Checksum            |  Instance ID  |      0          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |       0       |               Options                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |        Interface MTU          |      0        |0|0|0|M6|0|I|M|MS|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |                    DD sequence number                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |                                                                 |
     +-                                                               -+
     |                                                                 |
     +-                     An LSA Header                             -+
     |                                                                 |
     +-                                                               -+
     |                                                                 |
     +-                                                               -+
     |                                                                 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+--+
     |                               ...                               |

                  The OSPFv3 Database Description Packet

   The changed fields in the Database Description packet are described
   below.  The remaining fields are unchanged from [OSPFV3].

   Interface MTU
      The size in octets of the largest address-family specific datagram
      that can be sent out the associated interface without
      fragmentation.  The MTUs of common Internet link types can be
      found in Table 7-1 of [MTUDISC].  Interface MTU SHOULD be set to 0
      in Database Description packets sent over virtual links.

   M6-bit
      The IPv6 MTU bit - this bit indicates the sender is using a
      different IPv6 MTU than the MTU for the address family.

   IPv6 MTU TLV can be optionally carried in LLS block as described
   above.  This TLV carries the IPv6 MTU on the interface.  The length
   field of of TLV is set to 4 bytes.



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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              6 (TBD)          |               4               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           IPv6 MTU                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                          Format of IPv6 MTU TLV

   The IPv6 MTU TLV may appear in the LLS block only once.

2.8.  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 virtual link
   endpoints.  Although this requirement can be satisfied in IPv6
   unicast AFs, it will not function in other AFs as there will not be a
   routable global IPv6 address or forwarding path.  Therefore, virtual
   links are not supported in AFs other than IPv6 Unicast.




























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3.  Backward Compatibility

   In this section, we will define a non-capable OSPFv3 router as one
   not supporting this specification.  Each new AF will have a
   corresponding Instance ID and can interoperate with the existing non-
   capable OSPFv3 routers in an IPv6 unicast topology.  Furthermore,
   when a non-capable OSPFv3 router uses an Instance ID which is
   reserved for a given AF, no adjacency will be formed with this router
   since the AF-bit in the Options field will not be set in Hello
   packets.  Therefore, there are no backward compatibility issues.  AFs
   can be gradually deployed without disturbing networks with non-
   capable OSPFv3 routers.







































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4.  Security Considerations

   IPsec [IPsec]. can be used for OSPFv3 authentication and
   confidentiality as described in [OSPFV3-AUTH].  When multiple OSPFv3
   instances use the same interface, they all MUST use the same Security
   Association (SA), since the SA selectors do not provide selection
   based on OSPFv3 header fields such as the instance ID.  This
   restriction is documented in section 8 of [OSPFV3-AUTH].

   Security considerations for the OSPFv3 are covered in [OSPFV3].









































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5.  IANA Considerations

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

   The AF-bit is assigned from OSPFv3 Options field as defined in
   Section 2.2.

   IANA is requested to create a new registry, "OSPFv3 Instance ID
   Address Family Values". for assignment of address families.  Note
   that the Instance ID MAY be used for applications other than the
   support of multiple address families.  However, if it is being used
   for address families the assignments herein SHOULD be honored.

            +-------------+----------------------+--------------------+
            | Value/Range | Designation          | Assignment Policy  |
            +-------------+----------------------+--------------------+
            | 0           | Base IPv6 Unicast AF | Already assigned   |
            |             |                      |                    |
            | 1-31        | IPv6 Unicast AFs     | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 32          | Base IPv6 Multicast  | Already assigned   |
            |             |                      |                    |
            | 33-63       | IPv6 Multicast AFs   | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 64          | Base IPv4 Unicast AF | Already assigned   |
            |             |                      |                    |
            | 65-95       | IPv4 Unicast AFs     | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 96          | Base IPv4 Multicast  | Already assigned   |
            |             |                      |                    |
            | 97-127      | IPv4 Multicast AFs   | Already assigned   |
            |             | dependent on local   |                    |
            |             | policy               |                    |
            |             |                      |                    |
            | 128-255     | Unassigned           | Standards Action   |
            +-------------+----------------------+--------------------+

                 OSPFv3 Address Family Use of Instance IDs






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   o  Instance IDs 0-127 are assigned by this specification.

   o  Instance IDs in the range 128-255 are not assigned at this time.
      Before any assignments can be made in this range, there MUST be a
      Standards Track RFC including IANA Considerations explicitly
      specifying the AF Instance IDs being assigned.

   M6-Bit is assigned as defined in Section 2.7.

   A TLV type for IPv6 MTU TLV is assigned from OSPF LLS TLVs registry.









































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6.  References

6.1.  Normative References

   [IPV6]     Deering, S. and R. Hinden, "Internet Protocol,  Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [IPsec]    Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [OSPFV2]   Moy, J., "OSPF Version 2", RFC 2328, April 1998.

   [OSPFV3]   Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

   [OSPFV3-AUTH]
              Gupta, M. and S. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, June 2006.

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

6.2.  Informative References

   [ARP]      Plummer, D., "An Ethernet Address Resolution Protocol",
              RFC 826, November 1982.

   [LLS]      Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
              Young, "OSPF Link-local Signaling",
               draft-ietf-ospf-lls-05.txt, Work in progress.

   [MTUDISC]  Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
              November 1990.

   [ND]       Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861,
              September 2007.

   [PIM]      Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.









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Appendix A.  Acknowledgments

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

   Thanks to Tom Henderson and the folks at Boeing for implementing in
   quagga.

   Thanks to Nischal Sheth for review and comments.











































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Authors' Addresses

   Acee Lindem
   Redback Networks
   102 Carric Bend Court
   Cary, NC  27519
   USA

   Email: acee@redback.com


   Sina Mirtorabi
   Cisco Systems
   3 West Plumeria Drive
   San Jose, CA  95134
   USA

   Email: smirtora@cisco.com


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

   Email: akr@cisco.com


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

   Email: mjbarnes@cisco.com


   Rahul Aggarwal
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   USA

   Email: rahul@juniper.net






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