User guide

Controlling Route Flapping Through Route Dampening Configuring BGP
page 4-38 OmniSwitch AOS Release 7 Advanced Routing Configuration Guide March 2015
Enabling Route Dampening
Route dampening must be enabled before it effects routes. To enable route dampening on a BGP router,
enter the ip bgp dampening command, as shown:
-> ip bgp dampening
To disable route dampening, enter the following:
-> no ip bgp dampening
Configuring Dampening Parameters
There are several factors in configuring route dampening. These factors work together to determine if a
route should be dampened, and for how long. The values all have defaults that are in place when
dampening is enabled. It is possible to change these values, using the ip bgp dampening command with
variables. The variables for these parameters must be entered together, in one command, in order. This is
demonstrated in the following sections.
• Setting the Reach Halflife. The reach halflife is the number of seconds a route can be reached, without
flapping, before the penalty number (of flaps) is reduced by half. See “Setting the Reach Halflife” on
page 4-38 for instructions on how this is done.
• Setting the Reuse Value. The reuse value determines if a route is advertised again. See “Setting the
Reuse Value” on page 4-39 for instructions on how this is done.
• Setting the Suppress Value. The suppress value is the number of route withdrawals required before the
route is suppressed. See “Setting the Suppress Value” on page 4-39 for instructions on how this is
done.
• Setting the Maximum Suppress Holdtime. The maximum holdtime is the number of seconds a route
stays suppressed. See “Setting the Maximum Suppress Holdtime” on page 4-39 for instructions on how
this is done.
Setting the Reach Halflife
The reach halflife value is the number of seconds that pass before a route is re-evaluated in terms of
flapping. After the number of seconds set for halflife has passed, and a route has not flapped, then its total
flap count is reduced by half.
For example, if the reach halflife is set at 500 seconds, and a reachable route with a flap count of 300 does
not flap during this time, then its flap count is reduced to 150.
To change one variable to a number different than its default value, you must enter all of the variables with
the ip bgp dampening command in the correct order.
For example, to set the reach halflife value to 500, enter the halflife value and other variables with the
following command, as shown:
-> ip bgp dampening half-life 500 reuse 200 suppress 300 max-suppress-time 1800
In this example, the other variables have been set to their default values. The reach halflife is now set to
500. The default values for the reach halflife is 300.