Why OSPF type 1 LSA is returned to originate router ?

[zumitaka]

Hello, 

the topology in GNS3 is very simple. Router 5 and Router 6 are OSPF neighbours. Router 6 has loopback interface with IP 6.6.6.6/30 and is advertised in ospf. When i check in wireshark there is packet with source ip 10.10.10.1 (R5) and destination 10.10.10.2 (R6) that advertise 6.6.6.6 and 10.10.10.2 and both are on R6 router. Cant understand why should R5 return this LSA to R6 ?

[MHM Cisco World · Accepted solution]

because the link is Broadcast "network" not P2P this why the BDR send to DR the update and then the DR will re flood the update to all router in subnet.
change the link to be P2P and you will see one direction only.

[David Ruess]

Hello,

I think this is the nature of OSPF. Its goal is to share everything with everyone. In turn when R5 sends an LSA to R6 with R6's originating information it will discard it since it has its Router ID in the originating field. At least that's my understanding.

-David

[zumitaka]

MHM Cisco World thank you. I've tried to set link to be p2p and i don't see this LSA returned to originate router.