H3C S5600 Series Operation Manual page 396

Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches
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 5-10 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.
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.
As the peers in a peer group adopt the same route updating policy, peer group gains
more efficiency in route advertising.
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Chapter 5 BGP Configuration