OSPF Hello timer Question

Z3-Masterd

Hey guys,

If the OSPF hello timer is changed from the default of 10 to 15, does the dead timer stay at the default of 40, or will it automatically change to 60 ?

dmaftei

I suppose you mean HelloInterval and RouterDeadInterval; the answer would be no, when one is changed the other does not change automatically.

agustinchernitsky

Remember if you change that, you have to change it on all routes or they won't become neibors

romain

You should be carefully when deciding to update timers on your network.

It's not a simple change... but in a small topoly it could be easier...

gibby1801

dmaftei wrote:

I suppose you mean HelloInterval and RouterDeadInterval; the answer would be no, when one is changed the other does not change automatically.

The Dead Interval will automatically change to 60 if you change the hello interval from 10 to 15 because the Dead Interval by default equals 4 times the Hello Interval. I have just tested this on an 1811W running 12.4.6T AdvEnt. IOS.

bmauro

I can't test this at work - NetSim doesn't have this command. But, you can cofigure different values for the Hello and RouterDeadInterval

"ip ospf hello-interval" - Specifies the OSPF HelloInterval for an interface

"ip ospf dead-interval" - Specifies the OSPF RouterDeadInterval for an interface

I want to test this as well - but it looks like I'll have to wait until tonight.

bmauro

Update - as previously mentioned - if you change the HelloInterval it does update the Dead-Interval.

BUT - if you manually change the Dead-Interval it does NOT change the HelloInterval.

dmaftei

I should've qualified my answer... There is nothing in the specification (google "RFC 2328" to find it) requiring a timer to be automatically updated when another is changed, hence my answer. The fact that it happens in some routers (maybe all...) is an implementation detail.