OSPFv3 in NBMA Networks
OSPFv3 operates in NBMA networks almost exactly like OSPFv2. In particular, each interface
has an OSPF network type, with that network type dictating whether OSPFv3 needs to use a
DR/BDR and whether at least one router needs to have an OSPF neighbor command configured.
For example, when configuring Frame Relay with the IPv6 address on a physical interface or
multipoint subinterface, the OSPF network type defaults to “nonbroadcast,” which requires the use
of a neighbor command:
Jackson(config-if)# ipv6 ospf neighbor 3003::1
OSPFv3 neighbor relationships over NBMA networks take a relatively long time to form (a
minute or two), even on high-speed media, as they do in OSPFv2. This delay can lead to confusion
and may cause you to spend time troubleshooting a nonproblem.
Invariably, at some point in your studies (or lab exams), you will configure OSPFv2 or v3 over an
NBMA network and forget to include a neighbor statement. As a result, neighbors will not form and
you will have to troubleshoot the problem. A useful crutch you can use to help you remember that
NBMA OSPF peers require neighbor statements is the saying, “nonbroadcast needs neighbors.”
For completeness, you should be aware that it is possible to get OSPF neighbors to form over an
NBMA network without neighbor statements, if you change the interfaces’ network types from
their defaults. This is done using the ipv6 ospf network interface command, as it is in IPv4. The
same rules apply for IPv6, as explained in the Chapter 9 section “Designated Routers on WANs
and OSPF Network Types.”