Hi everyone, By replacing a Cisco 1921 router with a newer router, as the existing router was in OSPF Area 0 with its neighboring routers, the entire existing configuration was copied to the new router. But we encountered problems in establishing neighborhood with OSPF routing between the main router and remote sites was unsuccessful.
We tried several attempts to solve problems but it was no way out. (clear cache, clear OSPF process, reboot the router ...) and we ended up doing a rollback on the old router but the problem was not solved immediately. It was necessary to reconfigure all routers with a new Area (other than Area 0) to solve the problem.
What do you think the causes of this issue?
Looking forward to a return from you.
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