IBGP is used to ensure that all CE routers (BGP speakers) have a consistent view of the outside autonomous system routing paths. It has the following characteristics.
- Must reside within the same AS
- Neighbor must be defined on both sides
- Neighbors must be able to reach each other
Since BGP uses TCP, the IP reachability must available to ensure proper peering. For this reason, IBGP is usually run alongside another IGP, such as EIGRP or OSPF.
Stuck-in-Active: Journal of an IT-Network Administrator 