Overview
OSPFv3 is OSPF for IPv6. It reuses the same link-state logic as OSPFv2 — LSAs, LSDB, SPF, areas, neighbor states, and DR/BDR rules on multi-access segments — but runs over IPv6 with different addressing and configuration style.
Shared OSPFv2 concepts (neighbor states, DR/BDR, stub areas) live in OSPF Fundamentals and OSPF Neighbors, DR/BDR, Cost, and Areas. This page covers IPv6-specific behavior only.
How OSPFv3 differs from OSPFv2
| Topic | OSPFv2 (IPv4) | OSPFv3 (IPv6) |
|---|---|---|
| Address family | IPv4 prefixes | IPv6 prefixes |
| Typical config | router ospf + network | Per-interface ipv6 ospf |
| Neighbor addresses | IPv4 interface address | IPv6 link-local |
| All-router multicast | 224.0.0.5 | FF02::5 |
| DR/BDR multicast | 224.0.0.6 | FF02::6 |
| IP protocol number | 89 | 89 (unchanged) |
| Router ID | 32-bit dotted decimal | Same 32-bit RID format |
OSPFv2 and OSPFv3 are independent processes — they can run simultaneously on dual-stack routers but do not exchange routes with each other.
Prerequisites and configuration
Enable IPv6 routing globally, assign addresses, then enable OSPFv3 on each interface:
ipv6 unicast-routing ! interface GigabitEthernet0/0 ipv6 address 2001:db8:1::1/64 ipv6 enable ipv6 ospf 1 area 0 ! router ospfv3 1 router-id 1.1.1.1
OSPFv3 still requires a 32-bit Router ID in dotted-decimal format. On IPv6-only routers with no IPv4 address, configure router-id manually under router ospfv3.
Router ID selection matches OSPFv2 when IPv4 exists: highest loopback, then highest active physical IPv4. With no IPv4, you must set it explicitly.
Similarities worth remembering
- Point-to-point and point-to-multipoint links do not elect DR/BDR
- Neighbor discovery, adjacency states, and LSDB synchronization follow the same state machine as OSPFv2
- Area 0 backbone rules, stub areas, and SPF operation are conceptually the same
- NBMA topologies may still require static
neighborstatements (hub-and-spoke)
Hellos, LSAs, and area design behave like OSPFv2 — only the transport and addressing change.
Verification commands
show ipv6 ospf show ipv6 ospf interface show ipv6 ospf neighbor show ipv6 ospf database show ipv6 route ospf show ipv6 protocols
| Command | What it tells you |
|---|---|
show ipv6 ospf neighbor | Adjacency state — same FULL target as OSPFv2 |
show ipv6 ospf interface | Area, cost, timers, and link-local used for adjacency |
show ipv6 route ospf | IPv6 routes learned via OSPFv3 |
Neighbor addresses in output are link-local (FE80::/10), not global unicast — that is expected.
Exam checklist
OSPFv3 uses FF02::5 (all routers) and FF02::6 (all designated routers) — the IPv6 equivalents of 224.0.0.5 and 224.0.0.6.
ipv6 unicast-routing must be enabled before OSPFv3 routes install. Config is per-interface with ipv6 ospf <process> area <area>.
Do not assume Router ID auto-derives from IPv6 — without IPv4, manually configure router-id.
Quick review
- OSPFv3 = OSPF for IPv6; still protocol 89
- Enable with
ipv6 ospf 1 area 0on interfaces; process config underrouter ospfv3 - Neighbors use link-local addresses; multicasts FF02::5 / FF02::6
- 32-bit Router ID in IPv4 dotted-decimal format — manual on IPv6-only routers
- Verify with
show ipv6 ospf neighborandshow ipv6 route ospf