OSPF ABR Issue

[rawatmohinder]

Which of the following is an OSPF configuration parameter that is used on an ABR, but

not on an internal router?

A. A virtual link to area 0.

B. OSPF summarization command.

C. default-cost extension to the area command.

D. no-summary extension to the area stub command.

E. None of the above

Kindly explain your answers,..

Thanks

Mahi

[pkhatri]

Mahi,

The answer is D.

The 'no-summary' keyword is used on an ABR when configuring an area as a stub area. This keyword tells the ABR not to flood any type-3 LSAs into that area, but to only inject a type-3 default.

It does not make sense to use this keyword on an internal router since it is only the ABR that is responsible for generating type-3 summary LSAs.

Pls do take the time to rate posts that answer your queries...

Paresh

[pkhatri]

Actually, looking at the options again, answers A and C are also correct. Which means that the correct answers are A, C and D.

A is correct because you can only build virtual links between ABRs, not internal routers.

C is correct because it refers to the cost of the type-3 default injected into stub areas by ABRs. Once again, this is an ABR function only.

B is rather ambiguous - if it was the 'area range' command, it would be applicable to the ABR only. If it meant the 'summary-address' command, that applies to ASBRs, which could be internal routers..

Paresh