Internet Draft                                                   I. Chen
<draft-chen-ospf-transition-to-ospfv3-01.txt>                  A. Lindem
Category: Informational                                         Ericsson
                                                             R. Atkinson
Expires in 6 months                                         July 2, 2014

                  OSPFv3 over IPv4 for IPv6 Transition

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   This document defines a mechanism to use IPv4 to transport OSPFv3
   packets, in order to facilitate transition from IPv4-only to IPv6 and
   dual-stack within a routing domain.  Using OSPFv3 over IPv4 with the
   existing OSPFv3 Address Family extension can simplify transition from
   an OSFPv2 IPv4-only routing domain to an OSPFv3 dual-stack routing

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Table of Contents

   1. Introduction ....................................................3
   2. Encapsulation in IPv4 ...........................................4
      2.1. Source Address .............................................6
      2.2. Destination ................................................6
      2.3. Operation over Virtual Link ................................6
   3. IPv4-only Use Case ..............................................7
   4. Security Considerations .........................................7
   5. IANA Considerations .............................................8
   6. References ......................................................8

1.  Introduction

   To facilitate transition from IPv4 [RFC791] to IPv6 [RFC2460], dual-
   stack or IPv6 routing protocols should be gradually deployed.  Dual-
   stack routing protocols, such as Border Gateway Protocol [RFC4271],
   have an advantage during the transition, because both IPv4 and IPv6
   topologies can be transported using either IPv4 or IPv6.  Some
   IPv4-specific and IPv6-specific routing protocols share enough
   similarities in their protocol packet formats and protocol signaling
   that it is trivial to deploy an initial IPv6 routing domain by
   carrying the routing protocol over IPv4 initially, thereby allowing
   IPv6 routing domains be deployed and tested before decommissioning
   IPv4 and moving to an IPv6-only network.

   In the case of the Open Shortest Path First (OSPF) interior gateway
   routing protocol (IGP), OSPFv2 [RFC2328] is the IGP deployed over
   IPv4, while OSPFv3 [RFC5340] is the IGP deployed over IPv6.  OSPFv3
   further supports multiple address families [RFC5838], including both
   the IPv6 unicast address family and the IPv4 unicast address family.
   Consequently, it is possible to deploy OSPFv3 over IPv4 without any
   changes either to OSPFv3 or to IPv4.  During the transition to IPv6,
   future OSPF extension can focus on OSPFv3 and OSPFv2 can move into
   maintenance mode.

   This document specifies how to use IPv4 packets to transport OSPFv3
   packets.  The mechanism takes advantage of the fact that OSPFv2 and
   OSPFv3 share the same IP protocol number, 89.  Additionally, the OSPF
   packet header for both OSPFv2 and OSPFv3 places the OSPF header
   version (i.e., the field that distinguishes an OSPFv2 packet from an
   OSPFv3 packet) in the same location.

   This document does not attempt to connect an IPv4 topology and an
   IPv6 topology that are not congruent.  In normal operation, it is
   expected that the IPv4 topology within the OSPF domain will be
   congruent with the IPv6 topology of that OSPF domain.  In such cases,
   it is expected either that all OSPFv3 packets will be transported

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   over IPv4 or that all OSPFv3 packets will be transported over IPv6.

   If the IPv4 topology and IPv6 topology are not identical, the most
   likely cause is that some parts of the network deployment have not
   yet been upgraded to support both IPv4 and IPv6.  In situations where
   the IPv4 deployment is a proper superset of the IPv6 deployment, it
   is expected that OSPFv3 packets would be transported over IPv4, until
   the rest of the network deployment is upgraded to support IPv6 in
   addition to IPv4.  In situations where the IPv6 deployment is a
   proper superset of the IPv4 deployment, it is expected that OSPFv3
   would be transported over IPv6.

   Throughout this document, OSPF is used when the text applies to both
   OSPFv2 and OSPFv3.  OSPFv2 or OSPFv3 is used when the text is
   specific to one version of the OSPF protocol.  Similarly, IP is used
   when the text describes either version of the Internet protocol.
   IPv4 or IPv6 is used when the text is specific to a single version of
   the protocol.

2.  Encapsulation in IPv4

   Unlike 6to4 encapsulation [RFC3056] that tunnels IPv6 traffic through
   an IPv4 network, an OSPFv3 packet can be directly encapsulated within
   an IPv4 packet as the payload, without the IPv6 packet header, as
   illustrated in Figure 1.  For OSPFv3 transported over IPv4, the IPv4
   packet has an IPv4 protocol type of 89, denoting that the payload is
   an OSPF packet.  The payload of the IPv4 packet consists of an OSPFv3
   packet, beginning with the OSPF packet header with the OSPF version
   number set to 3.

   An OSPFv3 packet followed by an OSPF link-local signaling (LLS)
   extension data block [RFC5613] encapsulated in an IPv4 packet is
   illustrated in Figure 2.

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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ^
|   4   |  IHL  |Type of Service|          Total Length         |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|         Identification        |Flags|      Fragment Offset    |  |
|  Time to Live | Protocol 89   |         Header Checksum       | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Header
|                       Source Address                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                    Destination Address                        |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|                    Options                    |    Padding    |  v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ^
|       3       |     Type      |         Packet length         |  |
|                         Router ID                             | OSPFv3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Header
|                          Area ID                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  |
|          Checksum             |  Instance ID  |      0        |  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  v
|                        OSPFv3 Body ...                        |

       Figure 1: An IPv4 packet encapsulating an OSPFv3 packet.

                      | IPv4 Header   |
                      | OSPFv3 Header |
                      |               |
                      | OSPFv3 Body   |
                      |               |
                      |               |
                      | LLS Data      |
                      |               |

     Figure 2: The IPv4 packet encapsulating an OSPFv3 packet with
               a trailing OSPF link-local signaling data block.

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2.1.  Source Address

     For OSPFv3 over IPv4, the source address is the IPv4 interface
     address for the interface over which the packet is transmitted.
     All OSPFv3 routers on the link MUST share the same IPv4 subnet for
     IPv4 transport to function correctly.

2.2.  Destination Address

     As defined in OSPFv2, the IPv4 destination address of an OSPF
     protocol packet is either an IPv4 multicast address or the IPv4
     unicast address of an OSPFv2 neighbor.  Two well-known link-local
     multicast addresses are assigned to OSPFv2, the AllSPFRouters
     address ( and the AllDRouters address (  The
     multicast address used depends on the OSPF packet type, the OSPF
     interface type, and the OSPF router's role on multi-access

     Thus, for an OSPFv3 over IPv4 packet to be sent to AllSPFRouters,
     the destination address field in the IPv4 packet should be  For an OSPFv3 over IPv4 packet to be sent to
     AllDRouters, the destination address field in the IPv4 packet
     should be

     When an OSPF router sends a unicast OSPF packet over a connected
     interface, the destination of such an IP packet is the address
     assigned to the receiving interface.  Thus, a unicast OSPFv3 packet
     transported in an IPv4 packet would specify the OSPFv3 neighbor's
     IPv4 address as the destination address.

2.3.  Operation over Virtual Link

     When an OSPF router sends an OSPF packet over a virtual link, the
     receiving router is a router which is not directly connected to the
     sending router.  Thus, the destination IP address of the IP packet
     must be a reachable unicast IP address of the receiving router.
     Because IPv6 is the presumed Internet protocol and an IPv4
     destination is not routable, the OSPFv3 address family extension
     [RFC5838] specifies that only IPv6 address family virtual links are

     As illustrated in Figure 1, this document specifies OSPFv3
     transport over IPv4.  As a result, an IPv4 packet in which the
     destination field is a unicast IPv4 address assigned to the virtual
     router is routable, and OSPFv3 virtual links in IPv4 unicast
     address families can be supported.  Hence, the restriction in
     Section 2.8 of RFC 5838 [RFC5838] is removed.  If IPv4 transport,
     as specified herein, is used for IPv6 address families, virtual

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     links cannot be supported. Hence, it is RECOMMENDED to use the IP
     transport matching the address family in OSPF routing domains
     requiring virtual links.

3.  IPv4-only Use Case

   OSPFv3 only requires IPv6 link-local addresses to establish a routing
   domain, and does not require IPv6 global-scope addresses to establish
   a routing domain.  However, IPv6 over Ethernet [RFC2464] uses a
   different EtherType (0x86dd) from IPv4 (0x0800) and also from the
   Address Resolution Protocol (ARP) (0x0806) [RFC826] that is used with

   Some existing deployed link-layer equipment only supports IPv4 and
   ARP.  Such equipment contains hardware filters keyed on the EtherType
   field of the Ethernet frame to filter which frames will be accepted
   into that link-layer equipment.  Because IPv6 uses a different
   EtherType, IPv6 framing for OSPFv3 won't work with that equipment.
   In other cases, PPP might be used over a serial interface, but again
   only IPv4 over PPP might be supported over that interface.  It is
   hoped that equipment with such limitations will be replaced

   In some locations, especially locations with less communications
   infrastructure, satellite communications (SATCOM) is used to reduce
   deployment costs for data networking.  SATCOM often has lower cost to
   deploy than running new copper or optical cables for long distances
   to connect remote areas.  Also, in a wide range of locations
   including places with good communications infrastructure, Very Small
   Aperture Terminals (VSAT) often are used by banks and retailers to
   connect their stores to their main offices.

   Some widely deployed VSAT equipment has either (A) Ethernet
   interfaces that only support Ethernet Address Resolution Protocol
   (ARP) and IPv4, or (B) serial interfaces that only support IPv4 and
   Point-to-Point Protocol (PPP) packets.  Such deployments and
   equipment still can deploy and use OSPFv3 over IPv4 today, and then
   later migrate to OSPFv3 over IPv6 after equipment is upgraded or
   replaced.  This can have lower operational costs than running OSPFv2
   and then trying to make a flag-day switch to running OSPFv3.  By
   running OSPFv3 over IPv4 now, the eventual transition to dual-stack,
   and then to IPv6-only can be optimized.

4.  Security Considerations

   As described in [RFC4552], OSPFv3 uses IPsec [RFC4301] for
   authentication and confidentiality.  Consequently, an OSPFv3 packet
   transported within an IPv4 packet requires IPsec to provide

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   authentication and confidentiality.  Further work such as [ipsecospf]
   would be required to support IPsec protection for OSPFv3 over IPv4

   An optional OSPFv3 Authentication Trailer [RFC6506] also has been
   defined as an alternative to using IPsec.  The calculation of the
   authentication data in the Authentication Trailer includes the source
   IPv6 address to protect an OSPFv3 router from Man-in-the-Middle
   attacks.  For IPv4 encapsulation as described herein, the IPv4 source
   address should be placed in the first 4 octets of Apad followed by
   the hexadecimal value 0x878FE1F3 repeated (L-4)/4 times, where L is
   the length of hash measured in octet.

   The processing of the optional Authentication Trailer is contained
   entirely within the OSPFv3 protocol.  In other words, each OSPFv3
   router instance is responsible for the authentication, without
   involvement from IPsec or any other IP layer function.  Consequently,
   except for calculation of the value Apad, transporting OSPFv3 packets
   using IPv4 does not change the operation of the optional OSPFv3
   Authentication Trailer.

5.  IANA Considerations

   No actions are required from IANA as result of the publication of
   this document.

6.  References

6.1.   Normative References

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791, September

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

   [RFC2328]  Moy, J., "OSPF Version 2", STD54, RFC 2328, April 1998.

   [RFC5838]  Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
              R.  Aggarwal, "Support of Address Families in OSPFv3", RFC
              5838, April 2010.

6.2.  Informative References

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A

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              Border Gateway Protocol 4 (BGP-4)", RFC 4271, January

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC5613]  Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
              Yeung, "OSPF Link-Local Signaling", RFC 5613, August 2009.

   [RFC826]  Plummer, D., "Ethernet Address Resolution Protocol: Or
              Converting Network Protocol Addresses to 48.bit Ethernet
              Address for Transmission on Ethernet Hardware", STD 37,
              RFC 826, November 1982.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, June 2006.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC6506]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 6506, February

   [ipsecospf] Gupta, M. and Melam, M, Work in progress, "draft-gupta-
              ospf-ospfv2-sec-01.txt", August 2009.

Authors' Addresses

   I. Chen

   A. Lindem

   R. Atkinson

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