RFC 5340 describes Open Shortest Path First version 3 (OSPFv3) as a routing protocol for IPv6 networks. OSPFv3 initially supported IPv6 networks only, but it has been updated to support both IPv6 and IPv4 networks. OSPF algorithms and mechanisms, such as flooding, router types, designated router election, backbone areas, stub areas and NSSAs, and SPF calculations, remain the same. Changes are made for OSPF to support IPv6 addresses, address hierarchy, and IPv6 for transport. OSPFv3 uses multicast group FF02::5 for all OSPF routers and FF02::6 for all designated routers.

OSPFv3 Changes from OSPFv2

The following are the major changes from OSPFv2 to OSPFv3: 

• IPv6 only: This newer version of OSPF runs over IPv6 only.
• Support for IPv6 addressing: New LSAs have been created to carry IPv6 addresses and prefixes.
• Per-link processing: OSPFv2 uses per-subnet processing. With link processing, routers in the same link can belong to multiple subnets.
• Address semantics removed: Addresses are removed from the router and network LSAs. These LSAs now provide topology information.
• No authentication in OSPFv3: OSPFv3 uses IPsec, the IPv6 authentication scheme.
• New LSA: There is a new LSA for local-link flooding scope.
• New intra-area-prefix LSA: This LSA, which carries all the IPv6 prefix information, is similar to an OSPFv2 router and network LSAs.
• Neighbors identified by router ID: Neighbors are always identified by the router ID. This does not occur in OSPFv2 point-to-point and broadcast networks.
• Options field changes: Two Options bits, the R bit and the V6 bit, have been added to the Options field for processing router LSAs during the SPF calculation.

Note

In OSPFv3, the router IDs, area IDs, and LSA link-state IDs remain 32 bits. Larger IPv6 addresses cannot be used.

OSPFv3 Areas and Router Types

OSPFv3 retains the same structure and concepts as OSPFv2. The area topology, interfaces, neighbors, link-state database, and routing table remain the same. RFC 2740 does not define new area types or router types.

The OSPF areas shown in Figure 4-2 and the router types shown in Figure 4-4 remain the same. These are the router types in relationship to the OSPF areas:

• Internal router: An internal router is any router whose interfaces all belong to the same OSPF area. Such a router keeps only one link-state database.
• ABR: An ABR is connected to more than one area, where one area is Area 0. Such a router maintains a link-state database for each area it belongs to. ABRs generate summary LSAs.
• ASBR: This type of router injects external LSAs into the OSPF database (redistribution). These external routes are learned via either other routing protocols or static routes.
• Backbone router: A backbone router has at least one interface attached to Area 0.