3Com Switch 8800 Configuration Guide
Chapter 21 BGP Configuration
21-17
II. Configuring to filter the routes advertised by the BGP
Perform the following configuration in the BGP view.
Table 21-27
Configure to filter the routes advertised by the BGP
Operation
Command
Configure to filter the routes
advertised by the BGP
filter-policy
{
acl
-
number
|
ip-prefix
ip
-
prefix
-
name
}
export
[
routing
-
process
]
Cancel the filtering of the
routes advertised by the BGP
undo filter-policy
acl
-
number
|
ip-prefix ip
-
prefix
-
name
}
export
[
routing
-
process
]
By default, BGP does not receive the routing information advertised by other routing
protocols.
Note:
z
The
filter-policy import
command filters BGP route received from the neighbors.
The routes that cannot pass the filter will not be added to the routing table, and will
not be advertised to the neighbors.
z
The
filter-policy export
command filters all the advertised routes, including routes
imported by using the
import-route
command, and BGP routes learned from the
neighbors.
z
If the
filter-policy export
command does not specify which route to be filtered, then
the all the routes imported by the
import-route
command and the advertised BGP
routes will be filtered.
21.2.9 Configuring BGP Route Dampening
I. Configure BGP route dampening
The main possible reason for unstable route is the intermittent disappearance and
re-emergence of the route that formerly existed in the routing table, and this situation is
called the flapping. When the flapping occurs, update packet will be propagated on the
network repeatedly, which will occupy much bandwidth and much processing time of
the router. You have to find measures to avoid it. The technology controlling unstable
route is called route dampening.
The dampening divides the route into the stable route and unstable route, the latter of
which shall be suppressed (not to be advertised). The history performance of the route
is the basis to evaluate the future stability. When the route flapping occurs, penalty will
be given, and when the penalty reaches a specific threshold, the route will be
