How bgp and igp protocol interact with each other

[akachroo123]

I am little bit confused as to why we use bpp as well any igp protocol within a As.I am not able to find out any documentation on this subject.Please help

[Harold Ritter]

Generally speaking, BGP carries external routes (from other ASes) and the IGP carries internal routes.

The IGP learnt routes are usually also required to setup the iBGP session between two BGP speaking routers.

Let me know if I answered your question,

[akachroo123]

Isn,t ibgp so efficent that we have to configure it within As in addition to igp(osfp).Can you provide me some link on this topic,as i have tried many times,without success.

Thanks for replying.

[Harold Ritter]

It is not that iBGP is inefficient. It is rather that it was designed to carry lots of routes, way more than any IGP was design for.

On the other hand, for fast convergence purposes in your AS, an IGP will provide you better results than iBGP.

The idea is that BGP has been designed to work hand in hand with the IGP so that each do what they are best at.

Let me know if I answered your question,

[akachroo123]

If i am in a particular AS and i want to access a particular network,will it be igp or ibgp(i think igp have higher priority than ibgp).Next if a have to access another network which is in different AS,then is it that it will use ibgp within the same As and then ebgp and finally igp in that AS.

And i asked for some documentation?