OSPF convergence - WAN links

Fri Dec 17 13:33:41 UTC 2010

Hi all,

I have a network with a lot of FastEthernet WAN connections (some
metro-ethernet), and using the OSPF as IGP. Today, the OSPF timers are the
defaults (hello 10s, dead 40s, SPF initial timer 5s, etc). When a link comes
down, the convergence time takes ~45s (ok, it's right).
There are a lot of documents explaining about tuning OSPF convergence time,
but on LAN environments. I didn't find any references about this OSPF tuning
on WAN ethernet links (just serial, frame-relay, etc)  and things related to
it (such as packet loss, rtt, 'never lost of carrier', etc).

I think that, if the timers are aggressive, any flap on the ISP network can
cause a re-convergence... if the timers are high, the convergence time on
down links is high too.

What factors are you considering when tuning this OSPF timers on this type
of link? What 'tecnologies' are you using (such as Fast Hellos, incremental
SPF, etc) ?

Thanks,

Rafael