In a Transit AS, how do the internal routers within the Transit AS forward packets destined for the external networks using a scalable solution?
A.
Using the default route.
B.
Using the IGP routes where the external networks are redistributed into the IGP by the edge routers.
C.
Using the EBGP routes where the external networks are redistributed into the IBGP by the edge routers.
D.
Using the IBGP routes, then using recursive lookup based on IGP information to resolve the BGP next-hop.
Explanation:
The BGP route is installed in the routing table only if the IP address in the next-hop attribute is reachable according to the information already in the routing table. The BGP route is installed with a reference to that next-hop address. So the network will be reachable via an IP address, which may or may not be directly connected. Since there is no clear reference to a physical interface, the BGP route is installed in the IP routing table withut any information about outgoing interface. Reference: Configuring BGP on Cisco routers. P.4-30