OSPF Type 3 Summary LSA confusion

[Paheeradan Nagulan]

I have a question regarding the Summary LSA.

As you can see, R1 and R2 are ABRs which have legs in both Areas 0 and 1. 

If you look at the ospf database for R2 in area 0, you can see both the R1 and R2 are advertising the TYPE 3 LSA from Area 1(converted the Type 1 lsa from Area 1).  

But if I look at the OSPF database for area 1 on R1, why I'm not seeing the type 3 LSAs that were advertised by R2? I thought if the area 0 receives the Type-3 lsa, it will generate a new type-3 LSA and forward it out on a NON-Backbone area. If that theory is correct, I should have seen the type-3 lsa from R2 on the R1's area 1 LSDB?

[Harold Ritter · Accepted solution]

Hi @Paheeradan Nagulan ,

R1 will only advertise the type 3 LSAs received via area 0 from R2 to area 1 if it has them installed in its rib as inter area routes. In your scenario, R1 has the area 1 routes installed in its rib as intra area routes, hence it not advertising these type 3 LSAs received from R2 via area 0 to area 1.

Regards,

[Paheeradan Nagulan]

Hi @Harold Ritter ,

Perfect. This makes sense. Thanks for answering my question!

[Harold Ritter]

You are very welcome @Paheeradan Nagulan and thanks for the feedback

[Martin L]

without deep look at your issue please note 2 rules that might apply here:

When choosing the best route, an intra-area route is always better than a competing
interarea route, regardless of metric.
Step 2. If an ABR learns a Type 3 LSA inside a nonbackbone area, the ABR ignores
that LSA when calculating its own routes.

source: CCNP Route 642-902, Odom, W., Cisco Press 2010, 

Regards, ML
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[Paheeradan Nagulan]

Thanks @Martin L for mentioning that!