OSPFv3 is different from regular OSPF in an number of ways:
- Supports multiple address families: IPv4 is only supported in OSPFv2, OSPFv3 introduces support for IPv6 too!
- Additional LSA Types: For carrying IPv6 addresses.
- Removal of addressing semantics: Prefix information is no longer present in the OSPF packet headers. It is carried as a LSA payload instead, making the OSPF protocol address family independent.
- LSA flooding: There is a new link-state type field that is used to determine the flooding scope of the LSA.
- Packet format: OSPFv3 runs directly over IPv6; the number of fields in the packet header are reduced
- Router ID: The Router ID is used to identify neighbours regardless of network type. The ID must always be assigned manually with OSPFv3 on Cisco routers.
- Authentication: Neighbour authentication has removed and must be programed through IPSec extension headers.
- Neighbour Adjacencies: OSPFv3 router communication is handled by IPv6 link local addressing. Neighbours are not automatically detected over non broadcast multi access interfaces and must be specified using a link local address. IPv6 allows for multiple subnets to be tied to a single interface, using link local addressing allows interfaces to form adjacency even if a common subnet is not shared.
- Multiple Instance; OSPFv3 packets include a instance ID field that can be used to manipulate which routers are allowed to form adjacencies.