Lookat the following network carefully. The technician has configured all routers to advertise all connected links through BGP, and P4S-R2 through P4S-R4 to advertize all connected links via OSPF. At P4S-R4, 172.30.1.0/24 is not in the local BGP table or the local routing table. Why?

A.
P4S-R3 is learning 172.30.1.0/24 through iBGP, and therefore it will not re-advertize this route to its BGP peers, including P4S-R4.

B.
P4S-R3 is probably filtering 172.30.1.0/24, without examining the configuration on P4S-R2, you are unable to fix the problem.

C.
P4S-R4 has no path to the next hop for 172.30.1.0/24, P4S-R1.

D.
At P4S-R4, the next-hop for 172.30.1.0/24 is P4S-R1, and P4S-R1 is learning about the network between P4S-R1 and P4S-R2 through IBGP. BGP does not allow a route with an IBGP next hop to be installed in the local routing table.

Explanation:
When an AS provides transit service to other ASs and if there are non-BGP routers in the AS, transit traffic might be dropped if the intermediate non-BGP routers have not learned routes for that traffic via an IGP. The BGP synchronization rule states that if an AS provides transit service to another AS, BGP should not advertise a route until all of the routers within the AS have learned about the route via an IGP.