H3C Technologies H3C S7500E Series Switches - Manual (Page 215)

6-12
Route dampening
BGP route dampening is used to solve the issue of route instability such as route flaps, that is, a route
comes up and disappears in the routing table frequently.
When a route flap occurs, the routing protocol sends an update to its neighbor, and then the neighbor
needs to recalculate routes and modify the routing table. Therefore, frequent route flaps consume
large bandwidth and CPU resources and even affect network normal operation.
In most cases, BGP is used in complex networks, where route changes are very frequent. To solve the
problem caused by route flaps, BGP route dampening is used 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 flap occurs, 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 from being added into the routing table or being advertised to
other BGP peers.
The penalty value of the suppressed route will decrease to a 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 added into the routing table and advertised to other BGP peers.
Figure 6-12 BGP route dampening
Peer group
You can organize BGP peers with the same attributes into a group to simplify configurations on them.
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
accordingly.
When a peer is added into a peer group, the peer enjoys the same route update policy as the peer
group to improve route distribution efficiency.