Internet Draft                                                   I. Chen
<draft-ietf-ospf-transition-to-ospfv3-12.txt>                   Ericsson
Intended Status: Standards Track                               A. Lindem
Updates: 5838                                                      Cisco
                                                             R. Atkinson
Expires in 6 months                                        June 30, 2016

                  OSPFv3 over IPv4 for IPv6 Transition

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


   This document defines a mechanism to use IPv4 to transport OSPFv3
   packets.  Using OSPFv3 over IPv4 with the existing OSPFv3 Address
   Family extension can simplify transition from an OSPFv2 IPv4-only
   routing domain to an OSPFv3 dual-stack routing domain.  This document
   updates RFC 5838 to support virtual links in the IPv4 unicast address
   family when using OSPFv3 over IPv4.

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Table of Contents

   1. Introduction ....................................................3
      1.1. IPv4-only Use Case .........................................4
   2. Terminology .....................................................5
   3. Encapsulation in IPv4 ...........................................5
      3.1. Source Address .............................................7
      3.2. Destination ................................................7
      3.3. OSPFv3 Header Checksum .....................................7
      3.4. Operation over Virtual Link ................................8
   4. Management Considerations .......................................8
      4.1. Coexistence with OSPFv2 ....................................8
   5. Security Considerations .........................................9
   6. IANA Considerations .............................................9
   7. Acknowledgments .................................................9
   8. References .....................................................10
      8.1. Normative References.......................................10
      8.2. informative References.....................................10

1.  Introduction

   Using OSPFv3 [RFC5340] over IPv4 [RFC791] with the existing OSPFv3
   Address Family extension can simplify transition from an IPv4-only
   routing domain to an IPv6 [RFC2460], or dual-stack routing domain.
   Dual-stack routing protocols, such as Border Gateway Protocol
   [RFC4271], have an advantage during the transition, because both IPv4
   and IPv6 address families can be advertised using either IPv4 or IPv6
   transport. 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 transporting the routing protocol over IPv4,
   thereby allowing IPv6 routing domains to 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 to either OSPFv3 or to IPv4.  During the transition to IPv6,
   future OSPF extensions can focus on OSPFv3 and OSPFv2 can move to
   maintenance mode.

   This document specifies how to use IPv4 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 includes the OSPF header version

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   (i.e., the field that distinguishes an OSPFv2 packet from an OSPFv3
   packet) in the same location (i.e., the same offset from the start of
   the header).

   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 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
   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 Internet protocol.

1.1.  IPv4-only Use Case

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

     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 by that link-layer equipment.  Because IPv6 uses a
     different EtherType, IPv6 framing for OSPFv3 will not 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
     such interface.  It is hoped that equipment with such limitations
     will be eventually upgraded or 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 over 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 branches and stores to a central

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     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 OSPFv3.  By
     running OSPFv3 over IPv4 now, the eventual transition to dual-
     stack, and then to IPv6-only can be optimized.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Encapsulation in IPv4

   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 having its OSPF version field
   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.

   Since an IPv4 header without options is only 20 bytes long and is
   shorter than an IPv6 header, an OSPFv3 packet encapsulated in a
   20-byte IPv4 header is shorter than an OSPFv3 packet encapsulated in
   an IPv6 header.  Consequently, the link MTU for IPv6 is sufficient to
   transport an OSPFv3 packet encapsulated in a 20-byte IPv4 header.  If
   the link MTU is not sufficient to transport an OSPFv3 packet in IPv4,
   then OSPFv3 can rely on IP fragmentation and reassembly [RFC791].

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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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3.1.  Source Address

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

     While OSPFv2 operates on a subnet, OSPFv3 operates on a link
     [RFC5340].  Accordingly, an OSPFv3 router implementation MAY
     support adjacencies with OSPFv3 neighbors on different IPv4
     subnets.  If this is supported, the IPv4 data plane MUST resolve
     IPv4 addresses to layer-2 addresses using Address Resolution
     Protocol (ARP) on multi-access networks and point-to-point over LAN
     [RFC5309] for direct next-hops on different IPv4 subnets.  When
     OSPFv3 adjacencies on different IPv4 subnets are supported,
     Bidirectional Forwarding Detection (BFD) [RFC5881] cannot be used
     for adjacency loss detection since BFD is restricted to a single

3.2.  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 MUST be
     For an OSPFv3 over IPv4 packet to be sent to AllDRouters, the
     destination address field in the IPv4 packet MUST 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.

3.3.  OSPFv3 Header Checksum

     For IPv4 transport, the pseudo-header used in the checksum
     calculation will contain the IPv4 source and destination addresses,
     the OSPFv3 protocol ID, and the OSPFv3 length from the OSPFv3
     header (Appendix A.3.1 [RFC5340]).  The format is similar to the
     UDP pseudo-header as described in [RFC768] and is illustrated in

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     Figure 3.

      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
     |                       Source Address                          |
     |                    Destination Address                        |
     |     0         | Protocol (89) |     OSPFv3 Packet Length      |
               Figure 3: Pseudo-header for OSPFv3 over IPv4.

3.4.  Operation over Virtual Links

     When an OSPF router sends an OSPF packet over a virtual link, the
     receiving router is a router that might not be directly connected
     to the sending router.  Thus, the destination IP address of the IP
     packet must be a reachable unicast IP address for the virtual link
     endpoint.  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 supported.

     As illustrated in Figure 1, this document specifies OSPFv3
     transport over IPv4.  As a result, OSPFv3 virtual links can be
     supported with IPv4 address families by simply setting the IPv4
     destination address to a reachable IPv4 unicast address for the
     virtual link endpoint.  Hence, the restriction in Section 2.8 of
     RFC 5838 [RFC5838] is relaxed since virtual links can now be
     supported for IPv4 address families as long as the transport is
     also IPv4.  If IPv4 transport, as specified herein, is used for
     IPv6 address families, virtual links cannot be supported. Hence, in
     OSPF routing domains that require virtual links, the IP transport
     MUST match the address family (IPv4 or IPv6).

4.  Management Considerations

4.1.  Coexistence with OSPFv2

     Since OSPFv2 [RFC2328] and OSPFv3 over IPv4 as described herein use
     exactly the same protocol and IPv4 addresses, OSPFv2 packets may be
     delivered to the OSPFv3 process and vice versa. When this occurs,
     the mismatched protocol packets will be dropped due to validation
     of the version in the first octet of the OSPFv2/OSPFv3 protocol
     header. Note that this will not prevent the packets from being
     delivered to the correct protocol process as standard socket

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     implementations will deliver a copy to each socket matching the

     Implementations of OSPFv3 over IPv4 transport SHOULD implement
     separate counters for a protocol mismatch and SHOULD provide means
     to suppress the ospfIfRxBadPacket and ospfVirtIfRxBadPacket SNMP
     notifications as described in [RFC4750] and the ospfv3IfRxBadPacket
     and ospv3VirtIfRxBadPacket SNMP notifications as described in
     [RFC5643] when an OSPFv2 packet is received by the OSPFv3 process
     or vice versa.

5.  Security Considerations

   As specified in [RFC5340], OSPFv3 relies on IPsec [RFC4301] for
   authentication and confidentiality.  [RFC4552] specifies how IPsec is
   used with OSPFv3 over IPv6 transport.  In order to use OSPFv3 with
   IPv4 transport as specified herein, further work such as [ipsecospf]
   would  be required.

   An optional OSPFv3 Authentication Trailer [RFC7166] 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 octets.

   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 Apad value, transporting OSPFv3 packets
   using IPv4 does not change the generation or validation of the
   optional OSPFv3 Authentication Trailer.

6.  IANA Considerations

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

7.  Acknowledgments

   The authors would like to thank Alexander Okonnikov for his thorough
   review and valuable feedback and Suresh Krishnan for pointing out
   that clear specification for pseudo-header used in the OSPFv3 packet
   checksum calculation was required.  The authors would also like to
   thank Wenhu Lu for acting as document shepherd.

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8.  References

8.1.   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.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5309]  Shen, N., Ed., and A. Zinin, Ed., "Point-to-Point
              Operation over LAN in Link State Routing Protocols", RFC
              5309, October 2008.

8.2.  Informative References

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271, January

   [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.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
              10.17487/RFC0768, August 1980.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, DOI

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              10.17487/RFC5881, June 2010.

   [RFC4750]  Joyal, D., Ed., Galecki, P., Ed., Giacalone, S., Ed.,
              Coltun, R., and F. Baker, "OSPF Version 2 Management
              Information Base", RFC 4750, DOI 10.17487/RFC4750,
              December 2006.

   [RFC5643]  Joyal, D., Ed., and V. Manral, Ed., "Management
              Information Base for OSPFv3", RFC 5643, DOI
              10.17487/RFC5643, August 2009.

   [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.

   [RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
              Authentication Trailer for OSPFv3", RFC 7166, March 2014.

   [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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