Allied Telesis AT-8824 Guía de instalación descargar pdf (Pagina 148)

2-26 Release Note

Software Version 2.7.5

C613-10454-00 REV A

Applying Filters Before Advertising Routes

Routing protocols send their neighbours or peers information about the routes

in the router or switch’s RIB. You can use route filters to stop the router or

switch from advertising certain routes or routes with certain characteristics.

This gives you control over the routes that packets take through your network

and when leaving your network.

Filtering when using BGP to advertise routes

Filters act on all routes with a particular BGP attribute, or on particular routes.

The different types of filter you can use are

■ prefix lists

■ AS path lists

■ route maps

Applying prefix lists Prefix filtering rejects some of the routes from an update message, without

rejecting the whole update. This enables you to configure the router or switch

to send only routes for particular networks to a particular peer.

To use a prefix list as a prefix filter, use one of the commands:

add /jointfilesconvert/427458/bgp peer=ipadd remoteas=asn outfilter=prefixlist-name

[other-options]

set /jointfilesconvert/427458/bgp peer=ipadd outfilter=prefixlist-name [other-options]

add /jointfilesconvert/427458/bgp peertemplate=1..30 outfilter=prefixlist-name

[other-options]

set /jointfilesconvert/427458/bgp peeertemplate=1..30 outfilter=prefixlist-name

[other-options]

The outfilter parameter uses the prefix list to filter update messages that the

router or switch sends to the peer. If a prefix matches a prefix in the prefix list,

BGP removes that route from the update message. Otherwise, it leaves the

route in the update message and therefore advertises it to the peer.

The router or switch checks every route in the update message against every

entry in the filter, starting with the entry with the lowest entry number, until it

finds a match or gets to the end of the filter.

For example, to create a peer relationship on the local router or switch, with a

peer that has the IP address 192.168.1.1 and is part of AS 1, and prevent the

local router or switch from advertising routes from the 10.0.0.0/8 network, use

the commands:

add ip prefixlist=10_network entry=1 action=match

prefix=10.0.0.0/8

add /jointfilesconvert/427458/bgp peer=192.168.1.1 remotas=1 outfilter=10_network

You can also use a prefix list in a route map and apply the route map, as

described below.

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Allied Telesis AT-8824 Guía de instalación Pagina 148