OSPF

Comparison of OSPFv3 and OSPF Version 2

Much of OSPF version 3 is the same as in OSPF version 2. OSPFv3, which is described in RFC 5340, expands on OSPF version 2 to provide support for IPv6 routing prefixes and the larger size of IPv6 addresses.

1. In OSPFv3, a routing process does not need to be explicitly created. Enabling OSPFv3 on an interface will cause a routing process, and its associated configuration, to be created.

2. In OSPFv3, each interface must be enabled using commands in interface configuration mode. This feature is different from OSPF version 2, in which interfaces are indirectly enabled using the router configuration mode.

3. When using a nonbroadcast multiaccess (NBMA) interface in OSPFv3, users must manually configure the router with the list of neighbors. Neighboring routers are identified by their router ID.

4. In IPv6, users can configure many address prefixes on an interface. In OSPFv3, all address prefixes on an interface are included by default. Users cannot select some address prefixes to be imported into OSPFv3; either all address prefixes on an interface are imported, or no address prefixes on an interface are imported.

5. Unlike OSPF version 2, multiple instances of OSPFv3 can be run on a link.

6. OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP address among all loopback interfaces. If no loopback interfaces are present, the highest IP address in the router is chosen. You cannot tell OSPF to use any particular interface.

OSPFv3 does advertises IPv6 prefixes, but it does not advertise IPv4 prefixes, so in most OSPF shops that begin migration to IPv6, the routers run OSPFv2 for IPv4 support and OSPFv3 for IPv6 support, just like a network running EIGRP for IPv4 would then add configuration for EIGRP for IPv6.