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Qtech QSW-3900-24-Т-DC [158/313] Figure 10 diagram for bgp route dampening

Qtech QSW-3900-24-SFP-DC [158/313] Figure 10 diagram for bgp route dampening

QTECH Software Configuration Manual

11-157

The switches support automatic route summarization and manual route summarization. In the manual route

summarization mode, you can control the attribute of the summary routes and determine whether to send the specific

routes or not.

11.1.4.2 BGP route dampening

BGP route dampening is used to solve the problem of route instability. Route instability mainly takes the

form of route flaps, that is, a route appears and disappears repeatedly in the routing table.

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 10 Diagram for BGP route dampening

11.1.4.3 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.

A large-scale network can contain large amount of peers, lot of which adopt the same policies. Peer group

simplifies your configuration when you configure peers adopting the same policy.

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