3Com Switch 8807, Configuration Manual

Page: 375 / 883

Configuring BGP 375
By default, BGP does not receive the routing information advertised by other
routing protocols.
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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.
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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.
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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.
Configuring BGP Route
Dampening
Configure BGP route dampening
Route damping is primarily used to address the route instability problem. The main
possible reason for route instability is the intermittent disappearance and
re-emergence of the route that formerly existed in the routing table, and this
situation is called flapping. When 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 suppressed. With time going, the penalty value will decrease
according to power function, and when it decreases to certain specific threshold,
the route suppression will be eliminated and the route will be re-advertised.
Perform the following configuration in BGP view.
By default, route dampening is disabled.
Clear route dampening information
Perform the following configuration in user view to clear route dampening
information.
Cancel the filtering of the routes advertised by
other routing protocols
undo filter-policy
acl - number | ip-prefix ip - prefix - name }
export [ routing - protocol ]
Table 374 Configure to filter the routes advertised by other routing protocols
Operation Command
Table 375 Configure BGP route dampening
Operation Command
Configure BGP route dampening dampening [ half - life - reachable half - life - unreachable
reuse suppress ceiling ] [ route-policy route - policy - name ]
Cancel BGP route dampening undo dampening