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ABR that is also ASBR

dima krimerman


i have a question that i was asked in a job interview and i can't quite find the answer in the ospf RFCs or internet resources.

Supposeably we have an ASBR that on one interface connected to OSPF protocol , area 5, that is a NSSA.

on the second interface it's connected to area 0 , the backbone.

on the third interface it's connected to RIP (or EIGRP , not really importand, just other routing protocol).

the situation is tha the ASBR is also an ABR.

well, and the question is what limitations there would be to that router's activity , and what problems can occur in that scenario.

thx in advance

1 Reply 1


This is an interesting question. In terms of limitations, if you had a large enough network the OSPF database would become bloated, especially with Type 5 & Type 7 LSA's - essentially in duplicate due to the conversion that has to take place for the NSSA area. Maintaining such a Database could strain the processor on the device.

I would also say this would offer the potential for being a single point of failure within the network as if this device fails you will loose connectivity not only to Area 5 but to the external destinations too. This, of course, depends on whether this is the only router with this capablity. Other issues may arise if you were redistributing routes in to the external routing protocol in terms of filtering and again holding for example, an EIGRP topology table.

I'd be interested to hear other opinions on this question.



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