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. Thank you
hard to tell without any log messages etc..
deb ospf adj - would have most probably told your reason for the failing of the adjencency
what ospf state was it failing at?
How were you physically connecting this new rtr and what to?
Anything like differeing or mismatching ospf network types - Mtu duplicate router ids- access- control lists etc...can negate an adjacency from forming
Do you have any logging on this?
You stated in your OP that you couldnt establish an ospf adjacency but the logging you have attached since shows something entirely different.
It looks like you have Mgre tunnelling, specifically Tunnel 111 to various ospf peers, and you have some link inconsistency resulting in the flapping of not only ospf but BGP peers.
I would suggest you look into your connections:
opsf 10.199.248.6 down( 20.18.46) for 2mins then transions into full state again (20.20.40)
ospf 10.209.1.1 up (20:19:36) for 32 mins, then goes BGP 10.209.1.1goes down (20:52:10 then ospf 10.209.1.1 come up again. (20:52:21)