Internal and External BGP
Internal BGP (IBGP) is BGP peering relationship between routers in the
same autonomous system. External BGP (EBGP) is BGP peering relationship
between routers in different autonomous systems. BGP treats updates
from internal peers differently than updates from external peers.
In Figure 6-2, routers A and B are EBGP peers. Routers B, C, and D are
IBGP peers.