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DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch CLI Manual
122
config bgp dampening
Purpose
This command is used to configure BGP process’s dampening configurations
Syntax
config bgp dampening [ route_map <map_name 16> | clear_routemap | { state [enable |
disable] | half_life <min 1-45 > | reuse<value 1-20000> | suppress <value 1-20000> |
max_suppress_time <min 1-255 >| un_reachability_half_life <min 1-45>}(1)]
Description
The purpose of this command is to eliminate the dampening of routes and thus to avoid
unstable networks caused by flapping routes. The following describes the way it is achieved.
If a prefix is removed or is added, BGP will add a penalty on the route of 1000; if an attribute
of received route changes, BGP will add a penalty on the route of: 500.
Suppose that the half-life is configured to be 15min, the re-use value will be 800, and the
suppress value will be 1500.
When a route flaps (from up to down), add the penalty by 1000.Since the penalty is smaller
than the suppress value, BGP will work normally. It will send a withdraw message (an update
message) to the neighbors.
The penalty of the route will decrease as time elapses. Here we assume that if it passes 7.5
minutes, then the penalty of the route is 1000-500*7.5/15=750.
If another flap occurs (the route changes from down to up) then the penalty of the route will
be 1750, which is larger than the suppress value, and the route will be dampened. BGP will
not send an update message for this status change.
When the penalty of the route decreases and becomes smaller than the re-use value (800),
the route will not be dampened and the update message will be sent again.
Lastly, the max-suppress-time is the longest time the route may be suppressed. So, it
decides the maximum penalty a route may suffer regardless of the number of times that the
prefix is dampened. Here is the formula: Maximum-penalty= reuse-value*2max-suppress-
time/half-life
NOTE:
If the dampening ability is enabled and there are one or more dampened routes, the
dampened routes will be released to be the normal state immediately after we disable the
dampening function.
Parameters
state
- Specifies the BGP dampening function’s state.
half_life
- Specifies the time (in minutes) after which the penalty of the reachable routes will
be down, by half. The default setting is 15 minutes.
reuse
- If the penalty for a flapping route decreases enough to fall below this value, the route
is unsuppressed. The default setting is 750.
suppress
- A route is suppressed when its penalty exceeds this limit. The default setting is
2000.
max_suppress_time
- The maximum time (in minutes) a route can be suppressed. The
default setting is 60 minutes
un_reachablity_half_life
- Specifies the time (in minutes) after which the penalty of the
unreachable routes will be down, by half. The default setting is 15 minutes.
route_map
- This is to set the dampening running configuration..
clear_routemap
- This option will withdraw the route map configuration.
Restrictions
Only Administrator and Operator-level users can issue this command.
Example usage:
To disable the dampening function: