Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Manual do Utilizador descarregar pdf (Página 115)

Establishing a Peer-to-Peer Session

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Assigning Weight and Class Values to an AS

You can assign a weight class to any AS number and a weight value to a weight

class. Weights provide a way either to prefer or to avoid routes that pass through

certain ASs. The weights of each AS in a path are added, and the path with the

smallest total weight is the preferred path. An assigned weight can range from 1 to

15 plus an infinity value. Any path containing an AS weight of infinity is avoided.

AS weight classes allow you to assign multiple weight values to the same AS.

This feature allows you to consider an AS path differently for different networks.

For example, consider a situation in which two networks -- 192.32.1.0 and

192.32.2.0 -- are both reachable by two paths. The first path to each network

shares a common AS -- AS 5. The second path to each network also shares a

common AS -- AS 10. If you want to favor AS 5 in the path to 192.32.1.0 and AS

10 in the path to 192.32.2.0, you can assign one weight class to the AS in the path

to network 192.32.1.0 and another class to the AS in the path to 192.32.2.0.

When a BGP router receives a new route, it evaluates the route against any

existing accept policies. If after this evaluation the path still is to be used, the

router calculates the total weight of the path. Configure the same AS weights on

all BGP routers in an AS.

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Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Manual do Utilizador Página 115