3Com Switch 7700 Configuration Manual page 168

160 C 5: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
Perform the following configurations in BGP view.
The routes received by the BGP can be filtered, and only those routes that meet
certain conditions will be received by the BGP.
Table 114 Configuring BGP to Filter the Received Route Information
Operation
Configure received route filtering
Cancel the received route filtering
For details, see "Configuring BGP Route Dampening" on page 159.
Configuring the Filtering of Routes that are Distributed by BGP
The routes distributed by BGP can be filtered, and only those routes, which meet
the certain conditions, will be distributed by the BGP.
Perform the following configuration in the BGP view:
Table 115 Configuring the Filtering of Routes that are Distributed by BGP
Operation
Configure filtering of routes distributed by the
BGP
Cancel filtering of the routes distributed by
the BGP
By default, BGP will not filter the received distributed routes.
For details, see "Configuring BGP Route Filtering" on page 159.
Configuring BGP Route Dampening
The most possible reason for an unstable route is the intermittent disappearance
and re-emergence of the route that formerly existed in the routing table. This
situation is called route flapping. When flapping occurs, update packets are
propagated on the network repeatedly, which consumes router bandwidth and
processing time. Route dampening controls flapping.
Route dampening divides the route into a stable route and an unstable route. The
unstable route is not advertised. The history performance of the route is the basis
to evaluate the future stability. When route flapping occurs a penalty is given.
When the penalty reaches a specific threshold, the route is suppressed. Over time,
the penalty value decreases according to a power function, and when it decreases
to a specified threshold, the route suppression is eliminated and the route is
re-advertised.
Perform the following configurations in BGP view..
Table 116 Configuring BGP Route Dampening
Operation
Configure BGP route dampening
Command
filter-policy { acl-number | ip-prefix
ip-prefix-name [ gateway ip-prefix-name ] }
import
undo filter-policy { acl-number | ip-prefix
ip-prefix-name [ gateway ip-prefix-name ] }
import
Command
filter-policy { acl-number | ip-prefix
ip-prefix-name } export [ routing-process ]
undo filter-policy { acl-number | ip-prefix
ip-prefix-name } export [ routing-process ]
Command
dampening [ half-life-reachable
half-life-unreachable reuse suppress ceiling ] [
route-policy route-policy-name ]