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Community Member

Dual functionality ABR&ASBR

Could anybody know if an ABR might be also ASBR, and what happened with external routes if ABR has summary routes configuration for his area ? Could be present dual summarization as ABR and ASBR ?

Thanks

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Community Member

Re: Dual functionality ABR&ASBR

Yes an ABR can also be an ASBR.

Don't know exactly what you are asking about the summary routes. If the ABR is summarizing routes for injection into area 0, that will be the case regardless of what is going on with external routes.

If the area to which the ABR/ASBR is attached is a standard area, it will get the type 5 (external) LSAs just like the rest of the network. If the area to which the ABR/ASBR connects is a sub or totally stub, it should only send the type 5 LSA towards the backbone.

Of course, the ASBR can redistribute specific networks or it can be configured to summarize the external routes. This is configured seperately from area summarization (it even requires a different command - 'summary address' for the external vs. 'area range' for internal). The external routes would go into the backbone regardless of how the area is set up. Whether they went into the area would depend on the area type.

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