H3C Technologies H3C SR8800 - Manual (Page 220)

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When a route flap occurs, the routing protocol sends an update to its neighbor, and then the neighbor
needs to recalculate routes and modify the routing table. Frequent route flaps consume large bandwidth
and CPU resources, which could affect network operation.
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 routing table or being advertised to other BGP peers.
The penalty value of the suppressed route will decrease 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 routing table and advertised to other BGP peers.
Figure 82 BGP route dampening
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.
When a peer is added into a peer group, the peer has the same route update policy as the peer group
to improve route distribution efficiency.
NOTE:
If an option is configured for both a peer and its peer group, the last configuration takes effect.
Community
A peer group provides each peer in it with the same policy. A community provides a group of BGP
routers in several ASs with the same policy. Community is a path attribute advertised between BGP peers
without being limited by AS.
A BGP router can modify the community attribute for a route before sending it to other peers.
Suppress
threshold
Reusable
threshold
Penalty
value
Time
Half-life
Suppress time