Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Uživatelský manuál stáhnout pdf (Strana 23)

Exterior Gateway Protocols (BGP/EGP)

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Border Gateway Protocol (BGP)

The Border Gateway Protocol (BGP) is an exterior gateway protocol that border

routers use to exchange network reachability information with other BGP

systems. BGP routers form peer relationships with other BGP routers. Using an

entity called a BGP speaker, BGP peers transmit and receive current routing

information over a reliable transport layer connection, making periodic updates

unnecessary. BGP can be used both within and between autonomous systems.

BGP peers exchange complete routing information only when they establish the

peer connection. Thereafter, BGP peers exchange routing information in the form

of routing updates. An update includes a network number, a list of autonomous

systems that the routing information has passed through (the AS path), and other

path attributes that describe the route to a set of destination networks. When

multiple paths are available, BGP compares the path attributes to choose the

preferred path.

In addition to exchanging BGP information between autonomous systems, you

can use BGP to exchange BGP information between routers in the same AS. To

differentiate between these uses, the latter is called interior BGP (IBGP).

Exterior Gateway Protocol (EGP)

You use the Exterior Gateway Protocol to exchange network reachability

information between routers in different autonomous systems. An interior

gateway protocol (IGP), such as RIP or OSPF, is used within an AS to facilitate

the communication of routing information within an autonomous system. The

routers that serve as the end points of a connection between two autonomous

systems also run an exterior gateway protocol, such as EGP-2.

Routers establish EGP neighbor relationships to periodically exchange reliable

network reachability information. EGP neighbors exchange complete reachability

information, not just updates. The router uses this information to maintain a list of

gateways, the networks the gateways can reach, and the corresponding distances.

Chapter 10, “Customizing EGP Services

,” describes the use of EGP.

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Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Uživatelský manuál Strana 23