OSPF is a routing protocol for IP. It is a link-state protocol, as opposed to a distance-vector protocol like RIP. Think of a link as being an interface on a networking device. A link-state protocol makes its routing decisions based on the states of the links that connect source and destination machines. The state of a link is a description of that interface and its relationship to its neighbouring networking devices. The interface information includes the IPv6 prefix of the interface, the network mask, the type of network it is connected to, the routers connected to that network, and so on. This information is propagated in various type of link-state advertisements (LSAs).

A router’s collection of LSA data is stored in a link-state database. The contents of the database, when subjected to the Dijkstra algorithm, result in the creation of the OSPF routing table. The difference between the database and the routing table is that the database contains a complete collection of raw data; the routing table contains a list of shortest paths to known destinations via specific router interface ports.

OSPF version 3, which is described in RFC 2740 [RFC2740], supports IPv6. Implementing OSPFv3 for IPv6 expands on OSPFv2 to provide support for IPv6 routing prefixes. This section describes the concepts and tasks you need to implement OSPFv3 for IPv6 on your network.

Note: OSPFv3 is a separate protocol from OSPFv2 and is therefore an IPv6-only routing protocol. If you are running a dual-stack environment with OSPF you need separate routing processes for IPv4 and IPv6 (OSPFv2 and OSPFv3 respectively).