stub area and lsa 4

[sarahr202]

Hi every body

i hope every one is having good day.

I was reading about stubby area; The following link  describes it real good.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094aaa.shtml

However; I  am little confused  about lsa 4.   The link does not sa anything whether lsa 4 is allowed or not.

But here is my reasoning, Since  routers in stubby area do not know routes external to ospf domain, therefore there is no need for lsa4 to be propagated in  stubby area.

Is my understanding correct ?

If my understanding is correct;  it means lsa 4 is not flooded in stubby area.

thanks and have a great weekend, and to all my fellow americans happy veteran day.

[Reza Sharifi]

Hi Sarah,

Allowed LSAs in a Stub area are LSA Type-1, 2 and 3

and not allowed LSAs are 4 and 5.

HTH

[Reza Sharifi]

And just FYI

If an area is configured as stub no-summary

then:

Allowed LSAs are LSA Type-1, 2

and not allowed LSAs are 3,4 and 5.

have a great weekend

HTH

[Arun Nair]

I believed that the only LSA that can enter a stub area is a Type 3 LSA  and there can be no LSAs other than a summary LSA with default route sent into the Totally stub area, and the default route installed by the ABR for the area will do the routing. Am I wrong here, Reza??

[Peter Paluch · Accepted solution]

Reza,

If an area is configured as stub no-summary
then:
Allowed LSAs are LSA Type-1, 2 
and not allowed LSAs are 3,4 and 5.

In fact, it is slightly different. Even in totally stubby areas (stub no-summary), LSA-3 are - and must be - allowed because they carry the default route injected by ABRs. Without LSA-3, it would be impossible for a stubby area to have a default route to other areas, and would be in effect isolated from the rest of the network. What happens, however, is that ABRs in totally stubby areas do not originate any other LSA-3 for other inter-area networks. The only LSA-3 they generate is the one containing a default route. Hence, a totally stubby area still has a default route towards its ABRs, yet it does not know about networks in any other areas.

Best regards,

Peter