Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Uživatelský manuál stáhnout pdf (Strana 166)

Configuring IP Exterior Gateway Protocols (BGP and EGP)

10-4

308628-14.00 Rev 00

In the neighbor reachability phase, EGP is responsible for monitoring and

maintaining an established EGP neighbor relationship between two routers. Its

purpose is to ensure that the neighbors are operational and can provide reliable

network reachability information. Two neighbors will be able to exchange

network reachability information only if they are both in the up state and know

that they are both in the up state. This is the point at which neighbor reachability is

positively determined.

In the network reachability phase, EGP is responsible for determining which

networks are reachable through two EGP neighbors; that is, it provides the

network reachability information. This information provides a list of gateways,

the networks those gateways can reach, and their associated distances.

Two neighbors determine network reachability by exchanging poll messages and

routing update responses as follows:

• The active neighbor sends a poll message to a passive neighbor that it already

knows to be reachable. The poll message requests routing information from

the passive neighbor.

• The routing update response contains the routing information (the list of

gateways on the common network, the networks they can reach, and

associated distances). Both active and passive neighbors can send routing

update messages. The active neighbor usually sends a routing update response

after it sends a poll message. The passive neighbor usually sends a routing

update response in response to a poll message.

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Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Uživatelský manuál Strana 166