ospf converence

carl_townshend · ‎09-17-2008

Hi all ,with ospf I believe the dault hello time is 10 secs, and the dead is 40, does that mean it will take at least 40 seconds before ospf will react to an outage?

Giuseppe Larosa · ‎09-17-2008

Hello Carl,

in all cases where the dead interval expiration is needed to detect the failure your understanding is correct.

Another 5 seconds are waited before running the SPF algorithm so the convergence time can be up to 46 seconds.

If the problem is different and the interface goes down the time is the time to detect the interface state change + 5s.

The default timers can be changed to lower values and modern IOS can support sub-second hello interval or you can use BFD to speed up convergence (if supported).

Hope to help

Giuseppe

rohitrattan · ‎09-17-2008

Hello Carl,

Yes that's true. The hello time in OSPF is 10 seconds on Broadcast and Point to Point links and 30 seconds for Non Broadcast links e.g. Frame Relay and the dead timer is 4 times the hello. But this can be tweaked e.g.

(config-if)#ip ospf hello-interval ?

<1-65535> Seconds

(config-if)#ip ospf dead-interval ?

<1-65535> Seconds

minimal Set to 1 second

(should be same on both ends)

HTH

Regards

Rohit

satish_zanjurne · ‎09-17-2008

In order to have a rapid fault detection of topology changes, the hello timer value needs to be set to 1 second. The hold timer value, which is is four times that of the hello timer, also needs to be configured. There is a possibility of more routing traffic if the hello and hold timer values are reduced from their default values.

HTH..rate if helpful...