Wednesday, March 24, 2010

BGP Interview Questions For CCNA and CCNP Engineers


After IGP interview questions, I am posting BGP interview questions for CCNA and CCNP engineers. These questions are very basic and easy but during interview time no one knows how these will be asked by interviewer. So a good practice is to read it as much as we can so that we could provide the best answer to interviewer. Next post will cover about the basic questions of ip access-lists and prefix list. Read the questions below and in case any problem feel free to contact me.

1. BGP is IGP or EGP?
2. BGP is link state or distance vector protocol?
3. BGP uses which port?
4. When to use BGP?
5. Can I use BGP instead of any IGP?
6. Can I run two BGP process on single router?
7. What is Autonomous System?
8. Types of BGP routing table?
9. What is the BGP path selection criteria?
10. Define various BGP path attributes.
11. Why weight doesn’t fall under path attribute category?
12. What is confederation?
13. What is route reflector and why it is required?
14. What is no-synchronization rule?
15. Default BGP timers.
16. When does BGP use 0.0.0.0 router id?
17. Does route reflector come in actual path during traffic forwarding?
18. What is Site of origin aka SOO?
19. What is the cost of external and internal BGP routes?
20. Can we use local preference outside the autonomous system?
21. Does it require that BGP router-id should reachable in cloud?
22. What is recursive lookup in BGP and how it works?
23. What is the meaning of update source loopback?
24. If a static route is advertised in BGP without using update source what will be the next hop address in update?
25. Define various types of communities and why they are used?
26. If BGP neighbor state is showing idle what does it mean?
27. In Multihoming scenario if primary link gets fail, after how long traffic will be shifted to secondary link.
28. I am having two routes for remote destination but only single route is installing in routing table, what’s the reason for this?
29. How many links can be assigned for load balancing or sharing?
30. In eBGP I am establishing my neighbourship with loopback address but it’s not coming up. Please specify different reasons for not coming up.
31. Can we redistribute BGP in IGP? Please explain your answers.
32. What is cluster id?
33. I am receiving updates from eBGP peer, will the next hop change or not?
34. I am receiving updates from iBGP peer, will the next hop change or not?
35. A router is receiving same route from two different eBGP peers. The AS information contains in peer 1 is {65500, 65550, 65555} and in peer 2 is {65501, 65501}. But I want to make peer 1 preferred.
36. What is the difference between next-hop-self and update source loopback?
37. Define loop prevention mechanism in BGP.
38. What will happen if route reflector is not getting proper updates?
39. What will happen if route reflectors does not synchronize?
40. What is the advantage of using BGP AS Prepend?
41. Can we use BGP as backdoor link for customers instead of OSPF? If yes, please let us know what could the issues BGP create?
42. What is BGP PIC?
43. Use BGP as Link Protection in case of Dual PoP?
44. How to achieve Inter-AS Communication-MP-eBGP?
45. What can happen if Route Reflector(RR) is not getting proper route updates?
46. What is route reflector synchronization?
47. How to use BGP as PE-CE backdoor link?
48. What is Hierarchical FIB - BGP-PIC?
49. BGP Graceful Restart, NSR and NSF
50. BGP Redistribution Vs MPLS, which one you will select?
51. Best practices to define BGP Communities as per RFC 1998.
52. What is BGP RFC 3107 or What is BGP Label Update in IPv4?

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20 comments:

Lalit said...

Answer to Question 25

25. Define various types of communities and why they are used?

Answer: 4 Types of community:

1. internet—The Internet community.

2. no-export—Routes with this community are sent to peers in other subautonomous systems within a confederation. Do not advertise this route to an external BGP (eBGP) peer. External systems are those outside the confederation. If there is no confederation, an external system is any eBGP peer.

3. local-as—Send this route to peers in other subautonomous systems within the local confederation. Do not advertise this route to an external system.

4. no-advertise—Do not advertise this route to any peer (internal or external).

Now why they are used? Thats a good question.

Anonymous said...

what is the answer for Q 11

shivlu jain said...

weight is cisco proprietary

Anonymous said...

What are the answers to these question to cross reference against what i researched.

Vincent Lo said...

I am in serious need for a pump. Too much stress at work. Does anyone work on Huawei certification. Could someone please send me braindump and answer to exam questions.

Deepu said...

where i can find the ans of these all question?

nishit said...

pls provid ethe answers dude so that i can crossverify with my answers!!!

awaiting answers!!!!

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Anonymous said...

BGP

Anonymous said...

1. BGP is IGP or EGP? EGP
2. BGP is link state or distance vector protocol? PAth Vector
3. BGP uses which port? 179
4. When to use BGP? between multiple ASes
5. Can I use BGP instead of any IGP? yes
6. Can I run two BGP process on single router?yes
7. What is Autonomous System?
network maintained under single administration
8. Types of BGP routing table?

9. What is the BGP path selection criteria?
least no.of ASes
10. Define various BGP path attributes.AsPath,weight,MED,origin,nexthop,locPref
11. Why weight doesn’t fall under path attribute category?
cisco proprietery
12. What is confederation?
dividing ASes into sub ASes
13. What is route reflector and why it is required?
instead of full mesh form adjacnecy with RR
19. What is the cost of external and internal BGP routes?E-20,I-200
28. I am having two routes for remote destination but only single route is installing in routing table, what’s the reason for this?Best path is installed
29. How many links can be assigned for load balancing or sharing?1-6
35. A router is receiving same route from two different eBGP peers. The AS information contains in peer 1 is {65500, 65550, 65555} and in peer 2 is {65501, 65501}. But I want to make peer 1 preferred.increase the weight
37. Define loop prevention mechanism in BGP.Based on ASes if a router sees its own AS no.in the route it drops.

Mellow said...

Answer For Question No 6: 6. Can I run two BGP process on single router?
Answer: You cannot run more than one BGP process on Cisco IOS as it is a single threaded or monolithic Operating System and uses "Run to Complete Scheduler" Algorithm, uses IOS as single image and all processes uses same memory space for processing.
On Low end routers we only have single RP (Route Processor)

You can Run Multiple BGP Process on High End routers like Cisco CRS 1 onwards.. as Cisco Uses different IOS called Cisco IOS - XR, Which differentiates kernel from processes and each process can run on its own RP or separate memory space.

Anonymous said...

Can't we run multiple BGP on Virtual Router, Routing Instance ?

Harry said...

Can't we run multiple BGP instances on Virtual Router, Routing Instance ?

Mellow said...

we cannot run separate instance of routing protocol under VRF, we can define and use multiple address families under VRF For single instance of routing protocol

Praveen said...

shivlu can we have answer of these as well

type of routing table bgp has i didn't understand this question

pls tell and also provide answer

Anonymous said...

ANS 35: we can use local preference or AS path preped.

Dear blogger please provide anwers for the every questions.these questions are really tough.

Anonymous said...

ANS 35: we can use local preference or AS path preped.

Dear blogger please provide anwers for the every questions.these questions are really tough.

karan v. said...

ans 35: we can use local preference or AS-path preppend..

Dear blogger please share answers for all the questions..as these questions wil be very informative..hats off to you..

ANURAG GAUTAM said...

Can anyone please tell when to use mpls/vpn

Shivlu Jain said...

when you want core must be bgp free.