D-Link DXS-3600-32S CLI Guide - Page 83

Usage Guideline DXS-3600 Series 10GbE Layer 2/3 Switch CLI Reference Guide 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 1000500*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-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 routemap 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)# 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 75