The area IDs must match and the instance IDs must match in order for two routers running Open Shortest Path First version 3 (OSPFv3) to establish a neighbor adjacency? OSPFv3 is also called OSPF for IPv6. Like its IPv4 counterpart, OSPFv2, OSPFv3 requires that routers have identically configured area IDs, hello timers, and dead timers in order to establish neighbor adjacencies. In addition, OSPFv3 requires that instance IDs also match; instance ID do not exist in OSPFv2.

OSPFv3 allows multiple OSPF instances to run on a router. To keep track of each instance, OSPFv3 includes an instance ID field in the packet header. If no instance ID is specified on a link, the default value of 0 is used. When a router receives an OSPFv3 packet, it checks the instance ID in the packet header. If the instance ID in the header does not match the instance ID on the receiving interface, the router discards the packet even if the packet has a matching area ID.

Similar to OSPFv2, OSPFv3 requires that hello timers and dead timers match in order for routers to establish a neighbor adjacency. Hello timers are used to specify the amount of time between hello packets, which are used for neighbor discovery and maintaining neighbor relationships. By default, the hello timer is set to 10 seconds on pointtopoint and broadcast links and 30 seconds on nonbroadcast multiaccess (NBMA) links. The dead timer is used to specify the amount of time to wait before declaring a neighbor to be down. By default, the dead timer is set to four times the hello timer value.

Router IDs should not match between two routers running OSPFv3. The router ID is a 32bit value used to uniquely identify an OSPF router. By default, the router ID is the highest IPv4 loopback address configured on a router. If no loopback address is configured, the router ID is the highest IPv4 address among configured interfaces on the router. If no IPv4 addresses are configured on the router, the router ID must be manually configured before the OSPFv3 process will start. To manually configure the router ID, you should issue the routerid id command in router configuration mode.

Process IDs do not have to match in order for two routers running OSPFv3 to establish a neighbor adjacency. Process IDs are used to identify an OSPF process on a router. However, unlike instance IDs, process IDs are only locally significant to the router.