OSPF LSU static route

[AllezLom63194]

Hi the community,

Using Wireshark in area 0 ABR router,  I have seen LSU packet received concerning static network redistributed to OSPF area x on one ASBR router.

Is there a reason to have LSU packet received and received again for a static route redistributed in ASBR router ?

Of course nobody change the static route redistribution !:-)

Regards

[balaji.bandi]

Can you show us the wireshark information to understand what you referring here.

[AllezLom63194]

Hi BB,

Here is a screen shot of the captured packet.

Thank for you ideas.

Regards.

[balaji.bandi]

Can you post your OSPF config also ?

[AllezLom63194]

Hello BB,

I don't have access to the router config but I have asked a copy and I'll post it as soon as possible.

I think that maybe the router send LSU for statics routes every 30 minutes and I have recorded this packet.

Do yo think that the router that redistribut statics routes send periodically (30 minutes) LSU for theses routes ?

Regards,

[Joseph W. Doherty]

"Do yo think that the router that redistribut statics routes send periodically (30 minutes) LSU for theses routes ?"

Correct, I believe.  I recall (?) there's a 30 minute refresh of LSAs, even without changes.

I also recall (?) the RFCs don't specify "when" to refresh LSAs, but Cisco, to avoid overloading the network, paces out LSAs rather than sending them all out at the same time.

Static routes would be an external route, injected by an ASBR.  I.e. believe what you're seeing is "normal".

[Giuseppe Larosa]

Hello @AllezLom63194 ,

OSPF LSA data structures need to be refreshed before they expire .

An LSA can live up to 3600 seconds.

Cisco choice is to refresh them every 1800 seconds.

The new LSA will have a new greater sequence number and can be generated only by the same OSPF router (OSPF RID)  that generated the previous version  (it is the owner of the data structure).

LSA type 5 are flooded in all areas except stub areas or NSSA areas they are the only ones with AS scope.

All other LSA types have single area scope. However their information can be propagated by ABR when needed for LSA type 3 and LSA type 4 ( that describe current active ASBR nodes in the domain)

So yes what you see is normal.

Hope to help

Giuseppe