Huawei Quidway S5600 Series Operation Manual page 356

Operation Manual – Routing Protocol
Quidway S5600 Series Ethernet Switches-Release 1510
When route flaps occur, a route sends route update to its neighbors. Routers receiving
the update packets calculate the route over again and renew the routing table.
Therefore, frequent route flaps consume much bandwidth and CPU time. They even
affect the operation of network.
In most cases, BGP is applied in complicated networks where route changes are
frequent. In order to avoid the unfavorable affection caused by route flaps, BGP uses
route dampening to suppress the instable routes.
BGP route dampening uses penalty value to judge the stability of a route. A higher
penalty value indicates a more instable route. Each time a route flaps, BGP adds a
certain penalty value (fixed to 1000) to the route. When the penalty value excesses the
suppression threshold, the route will be suppressed and will neither be added to the
routing table nor send update packets to other BGP peers.
The penalty value of a suppressed route is decreased by half in each specific period
known as half-life. When the penalty value is decreased to a value less than the reuse
threshold, the route gets valid and is added to the routing table again. At the same time,
the BGP router sends corresponding update packets to its BGP peers.
Figure 5-9 Diagram for BGP route dampening
III. Peer group
Peer group is a set of peers that are the same in certain attributes. When a peer joins
into a peer group, the peer obtains the same configurations with those of the peer group.
When the configuration of a peer group changes, those of the group members change
accordingly.
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Chapter 5 BGP Configuration