Brocade TurboIron 24X Series Configuration Guide - Manual (Page 757)

Brocade TurboIron 24X Series Configuration Guide 723
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Configuring route flap dampening
The route flap dampening mechanism is based on penalties. When a route exceeds a configured
penalty value, the Layer 3 Switch stops using that route and also stops advertising it to other
routers. The mechanism also allows a route penalties to reduce over time if the route stability
improves. The route flap dampening mechanism uses the following parameters:
• Suppression threshold – Specifies the penalty value at which the Layer 3 Switch 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 Each time a route becomes unreachable or is withdrawn by a BGP4 UPDATE from a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 has a penalty value
greater than 2000, the Layer 3 Switch stops using the route. Thus, by default, if a route goes
down more than twice, the Layer 3 Switch stops using the route. You can set the suppression
threshold to a value from 1 – 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 five seconds. For example, if a route has a penalty of
2000 and does not receive any more penalties (it does not go down again) during the half-life,
the penalty is reduced to 1000 after the half-life expires. You can configure the half-life to be
from 1 – 45 minutes. The default is 15 minutes.
• Reuse threshold – Specifies the minimum penalty a route can have and still be suppressed by
the Layer 3 Switch. If the route's penalty falls below this value, the Layer 3 Switch
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 – 20000. The default is 750.
• Maximum suppression time – Specifies 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 – 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 configure route flap dampening globally or for individual routes using route maps. If you
configure route flap dampening parameters globally and also use route maps, the settings in the
route maps override the global values.
Globally configuring route flap dampening
To enable route flap dampening using the default values, enter the following command.
TurboIron(config-bgp-router)#dampening
Syntax: dampening [<half-life> <reuse> <suppress> <max-suppress-time>]
The <half-life> parameter specifies the number of minutes after which the route penalty becomes
half its value. The route penalty allows routes that have remained stable for a while despite earlier
instability to eventually become eligible for use again. The decay rate of the penalty is proportional
to the value of the penalty. After the half-life expires, the penalty decays to half its value. Thus, a
dampened route that is no longer unstable can eventually become eligible for use again. You can
configure the half-life to be from 1 - 45 minutes. The default is 15 minutes.
The <reuse> parameter specifies how low a route penalty must become before the route becomes
eligible for use again after being suppressed. You can set the reuse threshold to a value from 1 –
20000. The default is 750 (0.75, or three-fourths, of the penalty assessed for a one “flap”).
The <suppress> parameter specifies how high a route penalty can become before the Layer 3
Switch suppresses the route. You can set the suppression threshold to a value from 1 – 20000.
The default is 2000 (two “flaps”).