Flapping Links and OSPF

njorosam · ‎01-14-2009

Hi all,

I'm using OSFF in my network. I have my primary links via fibre and b/up via leased lines. Whenever there a flapping pri link, my remote site registers as down because OSPF keeps on looking for the best path using the fibre link which keeps on going up n down. Is there away whereby i can switch all traffic to leased line whenever service degrades within the fibre links without having to manually intervene & shut down the offending link?

Giuseppe Larosa · ‎01-15-2009

Hello Sammy,

OSPF with default timers can take up to 40 seconds to detect that the neighbor is dead.

if the link doesn't go down but it is still up/up the router has to wait for dead-interval timer expiration.

Depending on your IOS image you may think to use OSPF fast hellos that can reduce dead interval to 1 second with subsecond Hello frequency.

see

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fasthelo.html

Hope to help

Giuseppe