OSPF updates

DANMOH009

Im just reviewing OSPF,

I know it sends periodic updates. However i read that

"" OSPF, for example, also sends all summary information every 30 minutes by default"".

What does this mean, is the entire routing table only sent every 30 minutes??? And i take it this will just be the DR flooding to all its adjacent neighbors?
Can someone clear this up please.

Thanks

Zartanasaurus

OSPF doesn't send routing table updates, it sends database updates. LSAs have a 60m timer associated with them. OSPF routers refresh their LSAs every 30m. So that means non-DRs have to refresh their LSAs to the DR in order for the DR to refresh them to others.

DANMOH009

Zartanasaurus wrote: »

OSPF doesn't send routing table updates, it sends database updates.

I thought this was the case, completely forgot about the routers refreshing LSAs every 30mins. What does this consist of? i think im gonna read OSPF chapter again tonight.

MrBrian

If you do a "sho ip ospf database" you'll see all the various LSA's that make up the OSPF database. Each one of those LSA's is on its own timer where it will need to be updated if it hasn't heard anything within 30 mins. So with OSPF if there are no changes, then there will only be Hello packets exchanged.. so if nothing changes for a particular LSA within that 30 min timer, it will need to be refreshed. Each LSA is on its own timer, that way the whole database won't need to be updated at the same time, because if you had a large database it could potentially create a good amount of traffic.

It goes into great depth on this in Routing TCP/IP vol 1 fyi

DANMOH009

Ahhh got ya. Thanks Mr Brian.