186
NOTE:
BGP load balancing is applicable between EBGP peers, between IBGP peers, and between
confederations.
Settlements for problems in large-scale BGP networks
You can use the following methods to facilitate management and improve route distribution efficiency on
a large-scale BGP network.
•
Route summarization
Route summarization can reduce the BGP routing table size by advertising summary routes rather
than more specific routes.
The system supports both manual and automatic route summarization. Manual route
summarization allows you to determine the attribute of a summary route and whether to advertise
more specific routes.
•
Route dampening
Route frapping (a route comes up and disappears in the routing table frequently) causes BGP to
send many routing updates. It can 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 state change (from reachable to unreachable) occurs,
or a reachable route's attribute changes, 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 and cannot become the optimal route. When the penalty
value reaches the upper limit, no penalty value is added.
If the suppressed route does not flap, its penalty value gradually 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 usable again.
Figure 52
BGP route dampening
Suppress
threshold
Reusable
threshold
Penalty
value
Time
Half-life
Suppress time
