Understanding the OSPFv3 Difference

OSPFv3 changes the way it describes the network topology. All addressing semantics have been removed from the LSA header and from router-LSAs and network-LSAs. These two LSAs now describe the topology of the routing domain in a network-protocol-independent manner (using interface identifiers and router identifiers). New LSAs have been added to distribute IPv6 address information and data required for next-hop resolution.

In addition to the obvious address and processing modifications to handle IPv6 addressing, changes in OSPFv3 include the following:

• Authentication-related information is removed from the OSPF packet headers. Instead, OSPFv3 uses an authentication header in IPv6.
• OSPFv3 requires that each OSPF interface attached to a link be assigned a link-local unicast address.
• The option field for hello packets, database description (DD) packets, and LSAs has been expanded from 8 bits to 24 bits. In addition, two new LSA types have been added—link LSAs and intra-area prefix LSAs.
• The LSA flooding scope is more explicit in OSPFv3 and now appears in the LS type field. The LS type field also encodes a specific action to take for unknown LS types, allowing OSPF to function with unknown LS types instead of simply discarding them.
• The flooding process is modified to manage unrecognized LSAs and the new LSA flooding scope.
• The route calculation has been updated to handle modifications in the LSA database.

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