BGP Recursion Suppression in Case of Next Hop Flapping

Background

In some scenarios, if a large number of routes recurse to the same next hop that flaps frequently, the system will be busy processing reselection and re-advertisement of these routes, which consumes excessive resources and leads to high CPU usage. BGP recursion suppression in case of next hop flapping can address this problem.

Principles

After this function is enabled, BGP calculates the penalty value that starts from 0 by comparing the flapping interval with configured intervals if next hop flapping occurs. When the penalty value exceeds 10, BGP suppresses route recursion to the corresponding next hop. For example, if the intervals for increasing, retaining, and clearing the penalty value are T1, T2, and T3, respectively, BGP calculates the penalty value as follows:

Increases the penalty value by 1 if the flapping interval is less than T1.
Retains the penalty value if the flapping interval is greater than or equal to T1, but less than T2.
Reduces the penalty value by 1 if the flapping interval is greater than or equal to T2, but less than T3.
Clears the penalty value if the flapping interval is greater than or equal to T3.

When the penalty value exceeds 10, the system processes reselection and re-advertisement of the routes that recurse to a flapping next hop much slower.

Benefits

BGP recursion suppression in case of next hop flapping prevents the system from frequently processing reselection and re-advertisement of a large number of routes that recurse to a flapping next hop, which reduces system resource consumption and CPU usage.