IBGP "features"

IBGP sessions are special

To get the best path out of the network additonal IBGP routers need to be added.

IGP is used to route incomming traffic
IBGP is used to route outgoing traffic

Nexthops are passed unmodified
IBGP sessions require an IGP to work correctly
other hacks are possible. e.g. set nexthop self