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A question asked in Cisco Interview :

Which routing protocol will you use if you have 50 nodes in each area? Choose between OSPF , RIP and explain.

Edit: I worked with the above Question and came up with the following answer :

  1. RIP will not work for network having having hop count greater than 15 in any path because infinity is defined as 16 in RIP.
  2. RIP is good for small,stable and High Speed Networks while OSPF is good for large Dynamic Networks.
  3. RIP sends entire routing tale from router to router every 30 seconds(hence Consumes lot of bandwidth) while OSPF sends it's link state info every 30 minutes.OSPF routers also send each other small update message when they detect a change in network,moreover when routers exchange updates that reflect changes in the network they converge on a new representation of the topology quickly and accurately.
  4. RIP has slow convergency in large networks while it is faster in OSPF.In larger networks OSPF network is divided into logical Subdivisions called OSPF area.OSPF routers with in one area do not exchange topology updates with routers of other area(limited with in their area only)OSPF areas are connected by a backbone that is an area itself.A roiter that connects it's area to the backbone must maintain a topology database for both areas.Area border routers communicate with each other using special link message that contain short hand summarization of their respective topologies.

The above reasons supports OSPF over RIP

hope i have done well :)

Amol Sharma
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    There isn't a right answer (though I certainly know what I'd choose) - the interviewer is looking for a knowledge of different routing protocols and to see if you've formed well justified thoughts and opinions about them. – Shane Madden Jan 05 '12 at 05:25
  • i agree with you,i think interviewer wants OSPF as answer as it is advanced than RIP.but,i am not able to figure out neatly the reasons why i will prefer OSPF over RIP – Amol Sharma Jan 05 '12 at 05:28
  • If you'd have shouted "EIGRP!" when given a choice between OSPF and RIP, then the interviewer's going to know that you're invested in your chosen profession -- it's not about giving them the protocol that they want to hear, it's about showing that you've developed and justified your opinions internally instead of assuming that you should pick a given answer because it's "correct"; some would answer that question with "IBGP". In any case, this question doesn't have a 'correct' answer either, and is not a good fit for this site. Good luck! – Shane Madden Jan 05 '12 at 05:36
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    OSPF. Reason: RIP is evil. – Jed Daniels Jan 05 '12 at 05:46
  • @ShaneMadden - thnx for the advice :) – Amol Sharma Jan 05 '12 at 06:19

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The number of nodes in each subnet really has no bearing on which protocol the routers use the communicate. Given the information in the question there is absolutely no reasonable way to answer this Question. RIP is so simple that it's basically foolproof to get setup. OSPF will work much better for larger and more complex networks. EIGRP is a Cisco proprietary protocol, and isn't natively supported by as many OSes as the previous two.

Chris S
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