SUMMARY
The Border Gateway Protocol (BGP) is an interautonomous system protocol and is the principal route advertising protocol used in the Internet for external gateway operations. BGP is different from the routing protocols that have been explained thus far in this book in that routing decisions can be based on policy considerations, and need not be based just on the fewest number of hops, or link metrics.
BGP has a set of mechanisms to enable the network manager of a routing domain (in this case, an autonomous system) to control to whom traffic is sent, and from whom traffic is received, thus the idea of packet containment. This “to-from” capability exists to a limited extent in OSPF, but BGP uses policies to enforce its to-from filters.
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