© 2005 Cisco Systems, Inc. All rights reserved. BGP v Module Summary Because all transit autonomous systems are required to carry traffic originating from or destined to locations outside of that AS, a degree of interaction and coordination between BGP and the IGP is necessary, and special care should be taken to ensure consistency of routing information throughout the AS. Both EBGP and IBGP sessions forward BGP updates, but they do it in slightly different ways. An IGP is still needed inside a transit AS. The high-speed convergence offered by an IGP helps in the packet forwarding to external destinations. Configuring in a transit AS involves configuring IBGP neighbors, BGP synchronization, and IBGP sessions between loopback interfaces. The three common IBGP configuration problems concern session startup, route selection, and synchronization, and there are specific commands and procedures that can be used to solve those problems.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.22-2