OSPF LSA 3

[rabbit2]

Hello,

Can somebody explain to me why the below question has that answer?

x

From my understanding, the ABR creates type 3 LSA. So a type 3 LSA received from a nonbackbone area will be received in area 0. Further, the ABR generates a new type 3 LSA for other non-backbone area and lists himself as the advertising router. 

Or this question related to discontiguous ospf networks?

Thank you!

[Giuseppe Larosa · Accepted solution]

Hello @rabbit2 ,

see the following thread with a complete explanation from Peter Paluch.

https://community.cisco.com/t5/routing/ospf-abr-lsa-3-antiloop-prevention/m-p/4456461

LSA type 3 are not  flooded across areas but actually they are re-generated by ABR nodes only when needed and satisfy some conditions.

In this case receiving an LSA type 3 generated by another ABR node in a non backbone area does not allow the local node to re-generate it into the backbone area.

The thread defines these rules as anti loop rules.

This should explain the highlighted answer that is the local node can use the LSA type received on the non backbone area but it will not propagate it to the backbone area or other connected non backbone areas

Hope to help

Giuseppe