OSPF Statement Query

Hi,

Regarding the following statement- the part in bold
"In the case where there are no network changes, OSPF will use very little bandwidth (only sending hello packets). As soon as there is an outage, however, OSPF will flood the network as the change is sent to every router (and then every router notifies every other router about the change).

When it says this change is sent to every router (and then every "other" router) - "what other routers" are we talking about?

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Comments

jude56g

I think this is describing is how all OSPF enabled routers exchange information with all OSPF other routers in the area.

In other words
Router-A notifies Router-B, Router-C, & Router-D of the topology change.
Router-B notifies Router-C & Router-D.
Router-C notifies Router-B & Router-D
Router-D notifies Router-B & Router-C

This is how OSPF routers "know everything about everybody else"

SharkDiver

I believe they are just referring to the other routers in the affected area.

control

Yeah, it was just the fact it said "sent to every router" and then goes to say, "and every other router". To me, every router would have been easy to understand, but then it adds the every other router, so wasn't sure how to distinguish between the two.

So does it first of all notify directly connected neighbours, or everyone at once?

jude56g

Updates are sent out all OSPF enabled interfaces, so it will notifie the directly connected routers; then the "other routers" will send updates out of it's OSPF interfaces and so on until everyone receives the update.

NetworkVeteran

control wrote: »

OSPF will flood the network as the change is sent to every router (and then every router notifies every other router about the change Yeah, it was just the fact it said "sent to every router" and then goes to say, "and every other router". To me, every router would have been easy to understand, but then it adds the every other router, so wasn't sure how to distinguish between the two.

So does it first of all notify directly connected neighbours, or everyone at once?

The local router notifies every neighbor with which it has a full adjacency--that's the "sent to every router". Then those router notify every other router with which they have full adjacencies--that's the "and then every router notifies every other router." In multi-area OSPF there are some caveats, since intra-area notifications don't cross untouched into other areas, and sometimes don't cross at all.

Updates are sent out all OSPF enabled interfaces

Actually, OSPF doesn't flood updates out all OSPF-enabled interfaces, not even all non-passive OSPF-enabled interfaces. OSPF only floods to neighbors with which it has established adjacencies. "debug ip ospf flooding" shows this behavior clearly.

control

Thanks for info. Statement mkes sense now!