Is there a command under sh ip ospf that tells you where the last LSU was received from and how long ago. I swear I was using such a command a couple of weeks ago but cannot for the life of me remember what is was or if I dreamt it. The kit is a Cisco 6509... Thanks, Lee.
You may have been running debug? Otherwise, 'sh ip ospf database' will give you the advertising router and the age in seconds of the various link types (router links, network, etc). But you mentioned LSUs as opposed to LSAs. Of course, there can be many LSAs per LSU. So I don't know if that is what you were looking for?
What I had been doing is this: I have three 6509s in a triangle, running OSPF between them and a 3Com Netbuilder II with remote sites running of it. The Netbuilder and rmote sites are running RIP between them and the Netbuilder is converting RIP to OSPF and advertising to one of the 6509s.
I had been seeing the entire IP routing table being reset across all three 6509s and thought this due to a remote site coming up or flapping on the Netbuilder. I had been testing this by introducing a new remote site and bouncing it. However, instead of seeing the whole table being reset on the 6509, I only saw the individual route being introduced or dropping out i.e. the age time wasn't in sync with the majority of routes.
My "magic command" on the 6509 told me that the last LSU received came from the Netbuilder and the timer coincided with the age of the newest route i.e. the remote site, which is what I would expect if everything else was stable. However, getting back to the entire routing table reseting, the same command indicated that this was a result of an LSU recieved from the Netbuilder.
My problem is that I have just started the BSCN and have stacks of references and have no idea where (and if!!) I got this command from. I pretty sure it wasn't a debug as this was showing historical data rather than real time but conversly, I can't find the info under sh ip ospf!! I think I may have been dreaming... but it was vivid if it was!
OK, try this: 'sh ip ospf database xxx' where xxx is router, network, external, etc. This will show you the LSA age, LSA type, advertising router, sequence number, and a whole lot of other good info. Maybe that was it?
That will give you the reason why SPF was triggered and how long ago. But it does not give you the LSA. There is no such command in OSPF. This is actually a feature request to enhance 'sh ip ospf stat'.
With a 'sh ip ospf stat' you can see what type of lsa triggered SPF.
Then you can do a 'sh ip ospf data' and focus only on the lsa type mention by the previous command.
Check for a high sequence number and a small age.
Also I'm surprised that your full routing table reset. Normally, we do partial SPF calculation.
So 1 LSA should not affect the entire routing table.
Yes, I was surprised too. I've actually observed this happen quite a lot. Sometimes the routes will age for several hours, sometimes the routes may reset every few minutes or at extreme cases seconds. No one seems to notice a performance impact.
I know I sound like a looney re the LSU but I've just started the BSCN track and have been using a lot of external references and remember when I was inserting and dropping a remote router, being able to see where the last LSU was generated from... at least if I wasn't dreaming. I saw partial updates as you would expect, whcih tied in with the newest additional or deleted route. The full reset also indicated the 3Com as being the source and the time tied in as well.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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