Unanswered Question
Jan 5th, 2010
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hello friends,

i attended some technical interveiws and everytime i faced one question that why to use BGP when we have good protocols like OSPF or EIGRP?

really guys, i used to give answers but from my side i never satisfy with exact answer and also i am not confident about my answers.

can you please tell me, by which answer, i can prove above questions..

Thanks and Regards,


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Giuseppe Larosa Tue, 01/05/2010 - 02:31
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Hello Sourabh,

BGP is designed to interconnect different enterprises or organizations using different Autonomous Systems.

BGP provides scalability: actually the current internet could not be handled by any IGP: 300,000 routes!!

even ISIS cannot handle so many routes.

BGP has a rich toolset: BGP best path decision uses a hierarchy of criteria that goes beyond the calculation of a scalar metric. We could define BGP a protocol that uses a multi dimension vector/array of parameters as its metric.

For example think of BGP local preference or BGP weight : we can use this to prefer routes originated by different routers.

This allows for implementing complex policies that take in account multiple factors.

BGP is needed when  there are multiple exit points to the internet and you want to control how these exit points are used.

Hope to help


Mohamed Sobair Tue, 01/05/2010 - 02:42
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Hi sourabh,

The BGP protocol it self is not designed as an Intradomain IGP, its Inter domain routing protocol carries information between different ASs. unlike OSPF, which is designed as intrad domain IGP although it has heriarchical architecture but its not designed to carry information between different Autherities.

Another Good point for using BGP rather than Interior GW protocols like OSPF or Eigrp, is that flapping on the IGPs doesnt affect the BGP operation. This is one of the key factor behind the protocol design.



johnlloyd_13 Tue, 01/05/2010 - 05:37
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simply put it this way, BGP is used by organizations to connect to the internet. whereas, OSPF and EIGRP is used internally by organizations.


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