OSPF: ASBR in Backbone Area. How routes are sent to other area routers?

[rais]

How would OSPF behave when one of the backbone routers becomes an ASBR? Would the external routes be converted to type-5 automatically inside area backbone? How are these routes sent to other routers within say , area 1.

Thanks.

[Reza Sharifi]

ASBR routes/summary get injected in to area 0 by ABR router and they appear in are 0 as type 5 LSA.

How are these routes sent to other routers within say , area 1.

Depends on the area, if the area is a normal area, then it get all of the LSAs, including type 5.  But if for example area 1 is stub with no summary, then LSA types 3, 4,5 will not appear in it.  It only gets a default router from the ABR router.

HTH

Reza

[rais]

Reza,

Thanks for the reply.

What happens if the ASBR is part of backbone. Meaning there is no ABR between ASBR and backbone. Would the ASBR still inject routes as type-5 into backbone?

Thanks.

[Richard Burts]

Yes the ASBR will inject type 5 LSAs which will be received by all other backbone/area 0 routers.

HTH

Rick

[Pavel Bykov]

Yeah.

Say if you have routers connected like so: R1-R2-R3

And all of them are in area 0 (backbone), then if you enter the following on R2:

router ospf X

redistribute connected subnets

Then the R2 will become an ASBR even though it's a backbone router. If some interfaces (e.g. loopback100) is not covered by the network statement under router ospf process, the routes will appear in the RIB as O E2

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