OSPF Routes keep being refreshed every 50 Seconds!

[paul-giles]

Hi,

I have a LAN conisisting of 6500 Switches with SUP 720's running 12.2(18)SEX4, using OSPF throughout.

Though the network is stable and we do not see any connectivity issues, I have noticed that every 50 secs, the OSPF routes keep getting refreshed. I would not expect these routes to refresh every 50 secs unless possibly there was an OSPF timer inconsistancy.

I have attached a text file showing this.

Can anyone explain this behaviour and what might be the cause?

[pkhatri]

Hi Paul,

Unfortunately, the file has not come through - could you pls try again ?

Paresh

[paul-giles]

Sorry, here is the attcahed file

[pkhatri]

Hi Paul,

I think there is a reasonable explanation for this. The routes that you see getting refreshed are external routes. What protocol are you redistributing these routes from ? My guess is that the external OSPF routes are getting refresh every time you receive an update from this other protocol that is redistributed into OSPF. You will not find internal OSPF routes doing this.

Hope that helps - pls rate the post if it does.

Paresh

[paul-giles]

Thanks, but I only showed a sample of the full routing table. I can confirm that all OSPF routes, both internal and external show this same sympton.

[Harold Ritter]

You can use the "show ip ospf statistics detail" command to find out what is causing the SPF to be ran.

Hope this helps,

[paul-giles]

result - I tracked down a rogue router as shown as generating numerous SPF's and found a flapping interface on it (bouncing every 50 secs!). Shut down the interface and hey bingo.

Thanks very much

[Rakhmadian Purnama]

Hi guys,

I also have similar problem in Cat-6500, all my external route (redistribute static) always refresh after 10 - 60 sec.

But, I check there is no flapping on the router interface.

Any idea?

Thanks,

Rp