What is the need of IBGP when EIGRP and OSPF protocols are available?

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to understand the need of ibgp , the above secnario can be very helpful. 

as you can see we have AS100 , AS 200 and AS300. 

AS100 is advertising all internet routes to AS 300, so do AS 200 .

as 300 is a transit AS , It can use this information for itself also as it can also act as an isp  but we should focus on the  issue that  is how from one edge router of AS 300 to another edge router of AS 300  the routes of the adjacent AS 100, 200 will be advertised.

we have two solutions 

1. redistribute the whole bgp learnt routes into igp which can be eigrp , ospf or isis  or 

2. run ibgp on the routers  to advertise routes 

our first choice looks easy or more simple but its not  scalable as we are not talking about few  routes and secondly igp calculate the metric of each route on each router which is good for local lan to have the optimised  but it will overkill the cpu when it will be done for 

our second choice of running ibgp is quite handy in this case 

  as  it is not recquired to run on all the devices ,(ldp can help in that)

 secondly it can handle a lot of routes and no computation is done as bgp's behaviour of path selection is totally different than any igp

(P.S. we know we can use any of the above protocol to do the work , but we have to find the optimal one from the design prespective )