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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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► Request: These packets are used to obtain specific information from a<br />

neighbor. These packets are used in route server applications.<br />

5.8 Exterior Gateway Protocol (EGP)<br />

EGP is an exterior gateway protocol of historical merit. It was one of the first<br />

protocols developed for communication between autonomous systems. It is<br />

described in RFC 904.<br />

EGP assumes the network contains a single backbone <strong>and</strong> a single path exists<br />

between any two autonomous systems. Due to this limitation, the current use of<br />

EGP is minimal. In practice, EGP has been replaced by BGP.<br />

EGP is based on periodic polling using a hello/I-hear-you message exchange.<br />

These are used to monitor neighbor reachability <strong>and</strong> solicit update responses.<br />

The gateway connecting to an AS is permitted to advertise only those destination<br />

networks reachable within the local AS. It does not advertise reachability<br />

information about its EGP neighbors outside the AS.<br />

5.9 Border Gateway Protocol (BGP)<br />

The Border Gateway Protocol (BGP) is an exterior gateway protocol. It was<br />

originally developed to provide a loop-free method of exchanging routing<br />

information between autonomous systems. BGP has since evolved to support<br />

aggregation <strong>and</strong> summarization of routing information.<br />

BGP is an IETF draft st<strong>and</strong>ard protocol described in RFC 4271. The version<br />

described in this RFC is BGP Version 4. Following st<strong>and</strong>ard convention, this<br />

document uses the term BGP when referencing BGP Version 4.<br />

Chapter 5. Routing protocols 215

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