HPE FlexNetwork HSR6800 Configuration Manual page 203

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 64 BGP route dampening
Penalty
value
Suppress 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
•
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 to maintain sessions.
Using route reflectors can solve this issue. In an AS, a router acts as a route reflector, and other
routers act as clients connecting to the route reflector. The route reflector forwards the routing
information received from a client to other clients. In this way, all clients can receive routing
information from one another without establishing BGP sessions.
A router that is neither a route reflector nor a client is a non-client, which, as shown in
must establish BGP sessions to the route reflector and other non-clients.
Suppress
threshold
Reusable
threshold
Time
"BGP path attributes."
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Figure 65