© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Implementing BGP Explaining EBGP and IBGP

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Peers = Neighbors A BGP peer, also known as a BGP neighbor, is a specific term that is used for BGP speakers that have established a neighbor relationship. Any two routers that have formed a TCP connection to exchange BGP routing information are called BGP peers or BGP neighbors.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v External BGP When BGP is running between neighbors that belong to different autonomous systems, it is called EBGP. EBGP neighbors, by default, need to be directly connected.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Internal BGP When BGP is running between neighbors within the same AS, it is called IBGP. The neighbors do not have to be directly connected.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v IBGP in a Transit AS (ISP) Redistributing BGP into an IGP (OSPF in this example) is not recommended. Instead, run IBGP on all routers.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v IBGP in a NonTransit AS By default, routes learned via IBGP are never propagated to other IBGP peers, so they need full-mesh IBGP.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Routing Issues If BGP Not on in All Routers in Transit Path Router C will drop the packet to network Router C is not running IBGP; therefore, it has not learned about the route to network from router B. In this example, router B and router E are not redistributing BGP into OSPF.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Summary The key terms to describe relationships between routers running BGP are as follows: –BGP speaker, or BGP router –BGP peer, or neighbor –IBGP and EBGP EBGP neighbors are directly connected routers in different autonomous systems. IBGP neighbors are routers in the same AS that are reachable by static routes or a dynamic internal routing protocol. All routers in the transit path within an AS should run fully meshed IBGP.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v3.06-9