Enabling Open Shortest Path First version 3 (OSPFv3) on an interface enables the OSPFv3 routing process on the router. Additionally, the backup designated router (BDR) is elected before the designated router (DR) is elected. Finally, OSPFv3 supports multiple instances on a link. To enable OSPFv3 on an interface, you should issue the ipv6 ospf processid area areaid command in interface configuration mode. To enter router configuration mode for OSPFv3, you should issue the ipv6 router ospf processid command or the router ospfv3 [processid] command in global configuration mode.

The DR and BDR election process for OSPFv3 multiaccess segments is handled the same way as it is handled in OSPFv2: the BDR is elected first, and then the DR is elected. The router with the highest priority, as long as it has not already declared itself as the DR, becomes the BDR. Of those routers that have declared themselves as the DR, the router with the highest priority is elected to become the DR. If priority values are equal, the router with the highest router ID is elected. To change the OSPF priority of a router, you should issue the ip ospf priority value command, where value is an integer from 0 through 255. The default OSPF priority is 1, and a router with an OSPF priority of 0 will never be elected the DR or BDR.

OSPFv3 supports both IPv4 and IPv6. OSPFv3, which is described in Request for Comments (RFC) 2740, was developed as an enhancement to OSPFv2, which supports only IPv4. An OSPFv3 instance can support either IPv4 or IPv6, but not both. However, you can run multiple OSPFv3 instances on a single link. You can issue the ospfv3 processid area areaid {ipv4 | ipv6} [instance instanceid] command to enable OSPFv3 on an interface for a particular address family.

Network addresses are not included in the OSPFv3 process when the network command is issued. The network command is not required, because OSPFv3 is configured directly on each participating interface. Each IPv6 interface is designed to be configured with many different types of IPv6 addresses, such as sitelocal, linklocal, and global unicast. When you configure OSPFv3 on an interface, all IPv6 address prefixes are included? you cannot exclude certain prefixes and allow others. OSPFv3 does not send hello messages or linkstate advertisements (LSAs) over the IPv4 multicast addresses 224.0.0.5 and 224.0.0.6. Instead, OSPFv3 uses the IPv6 multicast addresses FF02::5 and FF02::6. All OSPFv3 routers receive packets destined for FF02::5, which is similar to the OSPFv2 allrouters multicast address 224.0.0.5. OSPFv3 DRs and BDRs receive packets destined for FF02::6, which is similar to the OSPFv2 allDR/BDR multicast address 224.0.0.6.

Unlike OSPFv2, OSPFv3 does not use Message Digest 5 (MD5) to secure communication. Instead, OSPFv3 uses IP Security (IPSec) to secure communication.