HP MSR Series Configuration Manual page 186

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
BGP route dampening solves the issue of route instability such as route flaps—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 recalculates routes and modifies the routing table. Frequent route flaps 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 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 BGP routing table or being
advertised to other BGP peers.
The penalty value of the suppressed route 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 added into the BGP routing table and advertised to other BGP peers.
Figure 53 BGP route dampening
Penalty
value
Suppress time
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
Route reflector
•
Half-life
"BGP path attributes."
174
Suppress
threshold
Reusable
threshold
Time