CCIE Routing & Switching Question of the Week: OSPFv3 Adjacencies

Examine the following exhibit. R1 and R6 cannot form OSPFv3 adjacencies, why?

A. You cannot use a network type of non-broadcast on an Ethernet interface
B. The IPv6 prefixes are not the same
C. The OSPF instance number doesn’t match
D. R6 is missing a neighbor statement
E. R6 has a priority of 0 (zero)

R1#sh run int e 0/0

Building configuration...

Current configuration : 207 bytes

interface Ethernet0/0

no ip address

ipv6 address FE80::1 link-local

ipv6 address 2005:DEAD:BEEF:16::1/64

ipv6 ospf 1 area 0 instance 1

ipv6 ospf neighbor FE80::6

ipv6 ospf network non-broadcast

R6#sh run int e0/0

Building configuration...

Current configuration : 201 bytes

interface Ethernet0/0

no ip address

ipv6 address FE80::6 link-local

ipv6 address 2005:DEAD:BEEF:61::6/64

ipv6 ospf 1 area 0 instance 6

ipv6 ospf network non-broadcast

ipv6 ospf priority 0

Reveal Answer

Answer: C.

In IPv6, the prefixes do not have to match for OSPFv3, the neighbors adjacencies are created between link local addresses. The network type of non-broadcast can be used on any type of network, it just needs to have at least one router with a neighbor statement. The other router doesn’t need a neighbor statement, it will respond to the unicast address of the originating router. The issue here is that the OSPF instance number has to match. The instance ID is typically used if there are more than one OSPFv3 process running on a set of routers and would like to group them together, similar to the EIGRP autonomous system number. The OSPF process number is locally significant, so we needed something that was passed between routers to identify the process between routers. This is defined in RFC 6969.

CCIE Routing & Switching Question of the Week Series

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