OSPF - network type mismatch
In order for an OSPF adjacency to form correctly between two OSPF routers, one of the criteria that is checked is the network type. Ideally the network type must be the same on both ends, however, it is possible to have different network types and still achieve an adjacency. For example:
- Broadcast with NBMA : A broadcast network type can form an adjacency with an NBMA network. However, you need to manually specify neighbors on the NBMA side. The broadcast side will consider the NBMA side as a broadcast and will try to establish adjacency with it.
- Point-to-Multipoint with Broadcast/NBMA/P2P: Point-to-Multipoint can form an adjacency with any network type. However, on the P2MP side, you need to manually specify the neighbors.
- P2MP with P2MNB: P2MP can form an adjacency with P2MNB, but you’ll need to manually specify neighbors on both sides.
- P2P with any other type: Point-to-Point can form an adjacency with any other network type. However, manual neighbor specification may be required depending on the other network type.
The above information is academic in nature! It should never be used to create an OSPF topology in a production network!
It’s always best to avoid network type mismatches, as they can lead to unexpected behavior and complicate troubleshooting. Always ensure that both sides of a link are using the same network type.\
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