Chapter 5. BGP Theory and Operation

The Border Gateway Protocol Version 4 (BGPv4, or more simply, just BGP) is the only interdomain, or exterior gateway, routing protocol in wide use today. To understand BGP, we must start by understanding what BGP defines as a routing domain.

Note

A routing domain, within BGP, is a network, or a set of networks, which share a common set of administrative policies toward external networks. Although a routing domain may contain many networks with different internal routing policies, a routing domain always appears as a single abstract “cloud,” with a single consistent routing policy, to outside entities.

The definition of a routing domain, within BGP, is intentionally fuzzy. A domain may be as small as a single ...

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