Conguring route ap dampening
A route ap is a change in the state of a route, from up to down or down to up. A route state change causes changes in the route tables
of the devices that support the route. Frequent route state changes can cause Internet instability and add processing overhead to the
devices that support the route.
Route ap dampening helps reduce the impact of route ap by changing the way a BGP4 device responds to route state changes. When
route ap dampening is congured, the device suppresses unstable routes until the number of route state changes drops enough to
meet an acceptable degree of stability. The Brocade implementation of route ap dampening is based on RFC 2439.
Route ap dampening is disabled by default. You can enable the feature globally or on an individual route basis using route maps.
NOTE
The device applies route ap dampening only to routes learned from EBGP
neighbors.
The route ap dampening mechanism is based on penalties. When a route exceeds a congured penalty value, the device stops using
that route and stops advertising it to other devices. The mechanism also allows route penalties to reduce over time if route stability
improves.
The route ap dampening mechanism uses the following parameters:
• Suppression threshold - Species the penalty value at which the device stops using the route. Each time a route becomes
unreachable or is withdrawn by a BGP4 UPDATE from a neighbor, the route receives a penalty of 1000. By default, when a
route penalty is greater than 2000, the device stops using the route. By default, if a route goes down more than twice, the
device stops using the route. You can set the suppression threshold to a value from 1 through 20000. The default is 2000.
• Half-life - Once a route has been assigned a penalty, the penalty decreases exponentially and decreases by half after the half-
life period. The default half-life period is 15 minutes. The software reduces route penalties every
ve seconds. For example, if a
route has a penalty of 2000 and does not receive any more penalties during the half-life, the penalty is reduced to 1000 after
the half-life expires. You can congure the half-life to be from 1 - 45 minutes. The default is 15 minutes.
• Reuse threshold - Species the minimum penalty a route can have and still be suppressed by the device. If the route penalty
falls below this value, the device un-suppresses the route and can use it again. The software evaluates the dampened routes
every ten seconds and un-suppresses the routes that have penalties below the reuse threshold. You can set the reuse threshold
to a value from 1 through 20000. The default is 750.
• Maximum suppression time - Species the maximum number of minutes a route can be suppressed regardless of how
unstable the route has been before this time. You can set the parameter to a value from 1 through 20000 minutes. The default
is four times the half-life. When the half-life value is set to its default (15 minutes), the maximum suppression time defaults to
60 minutes.
You can congure route ap dampening globally or for individual routes using route maps. If you congure route ap dampening
parameters globally and also use route maps, the settings in the route maps override the global values.
Globally conguring route ap dampening
Route ap dampening reduces the amount of route state changes propagated by BGP4 due to unstable routes. This in turn reduces
processing requirements.
To enable route ap dampening using the default values, enter the following command.
device(config-bgp-router)# dampening
Syntax: [no] dampening [ half-life reuse suppress max-suppress-time ]
Conguring route ap dampening
FastIron Ethernet Switch Layer 3 Routing
424 53-1003627-04
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