HP 6125XLG R2306-HP 6125XLG Blade Switch Layer 3 - IP Routing Configuration Gu - Page 176

Route summarization can reduce the BGP routing table size by advertising summary routes rather than more specific routes. The system supports both manual and automatic route summarization. Manual route summarization allows you to determine the attribute of a summary route and whether to advertise more specific routes. • Route dampening Route frapping (a route comes up and disappears in the routing table frequently) causes BGP to send many routing updates. It can consume too many resources and affect other operations. In most cases, BGP runs in complex networks where route changes are more frequent. To solve the problem caused by route flapping, you can use BGP route dampening to suppress unstable routes. BGP route dampening uses a penalty value to judge the stability of a route. The bigger the value, the less stable the route. Each time a route state change (from reachable to unreachable) occurs, or a reachable route's attribute changes, BGP adds a penalty value (1000, which is a fixed number and cannot be changed) to the route. When the penalty value of the route exceeds the suppress value, the route is suppressed and cannot become the optimal route. When the penalty value reaches the upper limit, no penalty value is added. If the suppressed route does not flap, its penalty value gradually decreases to half of the suppress value after a period of time. This period is called "Half-life." When the value decreases to the reusable threshold value, the route is usable again. Figure 49 BGP route dampening Penalty value Suppress threshold Suppress time Reusable threshold Time Half-life • Peer group You can organize BGP peers with the same attributes into a group to simplify their configurations. When a peer joins the peer group, the peer obtains the same configuration as the peer group. If the configuration of the peer group is changed, the configuration of group members is changed. • Community You can apply a community list or an extended community list to a routing policy for route control. For more information, see "BGP path attributes." • Route reflector 165