IP & Routing
OSPFv3 (IPv6)
OSPFv3 is the IPv6 version of OSPF, using the same link-state mechanics as OSPFv2 but running per-link instead of per-subnet and requiring a router ID in dotted-decimal form even without IPv4 configured.
What you need to know
- OSPFv3 is enabled per interface, not with network statements under the process, though modern IOS also supports address-family style network commands.
- A router ID is mandatory and must be a 32-bit dotted-decimal value; if no IPv4 address exists on the router, it must be configured manually.
- OSPFv3 runs directly over IPv6 using link-local addresses for neighbor communication, encapsulated in IPv6 rather than IPv4.
- Administrative distance remains 110, same as OSPFv2.
- OSPFv3 supports multiple address families (IPv4 and IPv6) under a single process using address-family ipv6/ipv4 unicast.
- DR/BDR election, cost calculation, and neighbor states are conceptually identical to OSPFv2.
- ipv6 unicast-routing must be enabled globally before OSPFv3 or any IPv6 routing will function.
Configuration commands
| Command | Mode | Purpose |
|---|---|---|
| ipv6 unicast-routing | config | Enable IPv6 routing globally, required before OSPFv3 operates. |
| ipv6 router ospf 1 | config | Create an OSPFv3 routing process with ID 1. |
| router-id 1.1.1.1 | config-router | Manually assign a dotted-decimal router ID to the OSPFv3 process. |
| interface gigabitethernet0/0 | config | Enter the interface to enable OSPFv3 directly on it. |
| ipv6 address 2001:db8:1::1/64 | config-if | Assign an IPv6 address to the interface. |
| ipv6 ospf 1 area 0 | config-if | Enable OSPFv3 process 1 on this interface in area 0. |
| ipv6 ospf priority 0 | config-if | Prevent this interface from becoming DR or BDR. |
| ipv6 ospf cost 10 | config-if | Manually set the OSPFv3 cost on the interface. |
| passive-interface gigabitethernet0/1 | config-router | Suppress OSPFv3 hellos on an interface while still advertising it. |
Verify it
- show ipv6 ospf neighbor
- show ipv6 ospf interface brief
- show ipv6 route ospf
- show ipv6 protocols
- show ipv6 ospf database
- show ipv6 interface brief
Common mistakes
- Forgetting ipv6 unicast-routing globally, so OSPFv3 never forms adjacencies.
- Missing a manually configured router ID on a router with no IPv4 addresses.
- Enabling OSPFv3 on an interface but forgetting to assign it to the correct area.
- Mismatched OSPFv3 process numbers assumed to matter for adjacency when only area and timers matter.
- Confusing OSPFv2 show commands (show ip ospf) with the required OSPFv3 equivalents (show ipv6 ospf).
Practise OSPFv3 (IPv6) in a real CLI
Generated labs, graded against the simulated network state.