I am wondering what (if anything) could make an OSPF router go from Full, directly to Loading. Could this happen if a fully adjacent (non-Cisco) remote peer suddenly sent a Link State Request packet? RFC 2328 says that routers should accept Link State Request packets in Full, but not exactly what to do after that.
This most of the time means that the adjacency was lost. check the connection, look for flaps, errors and etc. on the interface to this neighbor.
may be this links are helpfull to you
Devang- thanks. I should also have told you that the adjacency went back to being full. I would think that this sequence would not indicate corrupt LSAs. The sequence of events was:
During this time, or right before it, transit connectivity was lost. We did not see any flaps, but I am wondering if somehow the remote device noticed a corrupt LSDB and instead of cycling the adjacency, it just re-issued LS Requests (assuming it still had DBD from the last adjacency formation.
If the remote peer lost the adjacency (Full->Down) and the local OSPF adjacency is still up, then you can also see the local router report a Loading->Full when the remote OSPF peer comes back up.
I was rechecking a good routing reference (jeff doyle routing tcp/ip volume I second edition), and I dont think its possible to a router go from Full to Load and then to Full again. You can though be stuck in loading, but that's different.
Just to confirm: you are using: debug ip ospf adj to see this result?
is this something you can reproduce?
let us know,
Let me ask another question- during an adjacency formation, what will normal Cisco logs (NOT debug output) show? Do they show the whole process, or just loading to full? My logs show some init to down, and a lot of loading to full, but no 2-way, exstart, or exchange. Perhaps this is a question of interpreting log output.
We are NOT using debug at this point, as the network is stable now, and it's -very- mission critical.
I looked at the Doyle book as well, at the Moy book, and at the RFC. In the RFC, it does appear that you can go from Full to Loading. Hopefully, the following diagram looks okay, but if not, it's from RFC 2328, section 10.1. It appears that you can go from and to Loading from Full:
+----+ | +-------+
| LoadingDone |
when you eable the OSPF then you will find the whole the neighbourship establishment state step by step...
but you are able to see it in debuge...
if you want to tryit out then you can check it out in you testing routers...just enable OSPF and along with that start your debuge you are able to see the whole procedure or you can just make passive interface after the full establishment of neighbour ship...you are able to see the neighbourship will goes down and when you remove the passive interface then it will again establish the neighbourship...
hope this will help you
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