Router Server problem

hai all, I am simulating an IXP and this has 4 router servers which are connected to the ISP routers. I connected the 4 router server by means of Internal Bgp. This is as shown below IBGP ISP1------ RS1------- RS2 ------ ISP3 | | ISP2------ --------ISP4 Now the routes injected by ISP1 into R1 are received by ISP2. And there is exchange of routes between ISP3 and 4. But the routes send by ISP3 are not seen by ISP1 and ISP2. But RS1 has got those routes in its data base. These routes are not selected as best routes in the RS1 bgpd So to overcome this do u have any suggestions ??