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DXS-3600 Series 10GbE Layer 2/3 Switch CLI Reference Guide
75
7-17 bgp default ipv4-unicast
This command is used to enable the IPv4 unicast address family as the default address family for BGP peer session
establishment. The no form of this command disables the default IPv4 unicast address family for BGP peer session
establishment.
bgp default ipv4-unicast
no bgp default ipv4-unicast
Usage Guideline
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. When a route flaps (from up to down),
it will add a penalty value, of 1000, to the frame. Since the penalty is smaller than the
suppress value, BGP will function 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 *
2
Max-sup press-time / Half-life
You can verify your settings by entering the show ip bgp dampening parameters
command.
Note: If the dampening ability is enabled and there are one or more dampened
routes, the dampened routes will be released to function in the normal state
immediately after we disabled the dampening function.
Example
This example shows how to enable BGP dampening, set the half-life value to 20
minutes, the reuse value to 100, the suppress value to 6000, the maximum suppress
time to 120 minutes, and the un-reachability-half-life value to 20 minutes.
DXS-3600-32S#configure terminal
DXS-3600-32S(config)#router bgp 100
DXS-3600-32S(config-router)#bgp dampening 20 100 6000 120 20
DXS-3600-32S(config-router)#
Example
This example shows how to apply BGP damping to prefixes, filtered by the route-
map called ‘mymap1’.
DXS-3600-32S#configure terminal
DXS-3600-32S(config)#ip prefix-list pp1 permit 100.2.0.0/16
DXS-3600-32S(config)#route-map mymap1
DXS-3600-32S(config-route-map)#match ip address prefix-list pp1
DXS-3600-32S(config-route-map)#exit
DXS-3600-32S(config)#router bgp 100
DXS-3600-32S(config-router)#bgp dampening route-map mymap1
DXS-3600-32S(config-router)#
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