Mobility

How to Construct a Correct and Scalable IBGP Configuration

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Executive Summary

The Internet's current interdomain routing protocol, BGP (Border Gateway Protocol), has two modes of operation: eBGP (external BGP), used to exchange routing information between autonomous systems, and iBGP (internal BGP), used to propagate that information within an Autonomous System (AS). In a "Full mesh" iBGP configuration, every router has a BGP session with every border router in the AS. Because a full mesh configuration has a large number of iBGP sessions and does not scale well, configurations based on route reflectors are commonly used for intra-AS route dissemination. Unfortunately, route reflector configurations violate important correctness properties, including loop-free forwarding and complete visibility to all eBGP-learned best routes, especially in the face of router and link failures.

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