Good OSPF question.

Unanswered Question
Sep 21st, 2009

This is a question from Wendell Odom CCIE Certification Guide book, 3td edition, Chapter 9, question 9. I not sure if the asnwer in the appendix is correct. So I post it here to see if someone agrees with me. There might be more than one right answers.


Paulo Roque

R1 is an OSPF ASBR that injects an E1 route for network into the OSPF

backbone area. R2 is an ABR connected to area 0 and to area 1. R2 also has an Ethernet

interface in area 0, IP address, for which it is the designated router. R3 is a

router internal to area 1. Enough links are up and working for the OSPF design to be

working properly. Which of the following are true regarding this topology? (Assume no

other routing protocols are running, and that area 1 is not a stubby area.)

* a. R3's cost for the route to will be the cost of the route as it was injected into the

OSPF domain by R1, without considering any internal cost.

* b. R3's cost for the route to will include the addition of R3's cost to reach R1,

plus the external cost listed in the LSA.

* c. R3's cost for the route to will be the same as its cost to reach ABR R2.

* d. R3's cost for the route to will be the sum of its cost to reach ABR R2 plus

the cost listed in the type 3 LSA created for by ABR R2.

* e. It is impossible to characterize R3's cost to because R3 uses a summary type

3 LSA, which hides some of the costs.

10. R1 and R2 each connect via Fast Ethernet interfaces to the same LAN, which should be in

I have this problem too.
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Giuseppe Larosa Mon, 09/28/2009 - 13:43

Hello Paulo,

I would choice two answers

b) because external route is O E1 and so internal cost has to be considered and added to seed metric

d) because for R3 that net comes from another area

Hope to help



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