HPE 5800 Series Configuration Manual page 186

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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
large bandwidth and CPU resources, which could affect network operations.
In most cases, BGP is used in complex networks, where route changes are more 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 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 62 BGP route dampening
Penalty
value
Suppress time
Half-life
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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.
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Community
When you define a routing policy, to facilitate configuration and maintenance, you can use the
community list and extended community list as filters, instead of IP prefix list, ACL, or AS_PATH.
For more information, see
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Route reflector
IBGP peers must be fully meshed to maintain connectivity. If n routers exist in an AS, the
number of IBGP connections is n(n-1)/2. If a large number of IBGP peers exist, large amounts
of network and CPU resources are consumed.
Suppress
threshold
Reusable
threshold
Time
"Path attributes."
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