The figure shows the logical network architecture of a migration project.

OSPF adjacency establishment requires compatible interface parameters, including area IDs, Hello and Dead intervals, authentication settings, and unique router IDs between neighboring devices.

In the displayed migration topology, R1 and R3 retain their Area 1 connection and can establish an OSPF adjacency.

After R4 replaces the original R2–R3 connection, R2 and R4 can also establish an adjacency because their router IDs differ, assuming compatible interface configuration.

However, R3 and R4 cannot establish an OSPF neighbor relationship. They are not directly connected in the displayed topology and share the same router ID because R4 was configured using R3 ' s backup.

The Area 0 connection between R1 and R2 is unchanged, so their established OSPF neighbor relationship remains unaffected.