Example BGP Using Loopback Addresses

6-44 Building Scalable Cisco Internetworks (BSCI) v3.0

The neighbor update-source command should be used on both routers. If router B points to loopback address 3.3.3.3 of router C, and router C points at loopback address 2.2.2.2 of router B, and neither uses the neighbor update-source command, the BGP session between these routers will not start.

Router B would send a BGP open packet to router C with the source IP address being either 10.1.1.1 or 10.2.2.1. Router C would review the source IP address and attempt to match it against its list of known neighbors. Router C would not find a match and would not respond to the open message from router B.

© 2006 Cisco Systems, Inc. Implementing BGP 6-45

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