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.