1RTERTB#ROUTER BGP 100NEIGHBOR 150
175.10.40.1
RTE
RTB#
router bgp 100
neighbor 150.10.30.1 remote-as 100
neighbor 175.10.40.1 remote-as 400
network 190.10.50.0
RTC#
router bgp 400
neighbor 175.10.40.2 remote-as 100
network 175.10.0.0
An important point to remember, is that when a BGP speaker receives an
update from other BGP speakers in its own AS (IBGP), the receiving BGP
speaker will not redistribute that information to other BGP speakers in
its own AS. The receiving BGP speaker will redistribute that information
to other BGP speakers outside of its AS. That is why it is important to
sustain a full mesh between the IBGP speakers within an AS.
In the above diagram, RTA and RTB are running IBGP and RTA and RTD are
running IBGP also. The BGP updates coming from RTB to RTA will be sent to
RTE (outside of the AS) but not to RTD (inside of the AS). This is why an
IBGP peering should be made between RTB and RTD in order not to break the
flow of the updates.