Configuring BGP Recursion Suppression in Case of Next Hop Flapping

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

Usage Scenario

If a large number of routes recurse to the same next hop that flaps frequently, the system will be busy processing changes of these routes, which consumes excessive system resources and leads to high CPU usage. To address this problem, configure BGP recursion suppression in case of next hop flapping.

By default, BGP recursion suppression in case of next hop flapping is enabled. 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.

Pre-configuration tasks

Before configuring BGP recursion suppression in case of next hop flapping, configure basic BGP functions.

Procedure

Run system-view
The system view is displayed.
Run bgp { as-number-plain | as-number-dot }
The BGP view is displayed.
Run ipv4-family unicast
The IPv4 unicast address family view is displayed.
Run undo nexthop recursive-lookup restrain disable
BGP recursion suppression in case of next hop flapping is enabled.

If you do not care about whether the system is busy processing route selection and advertisement and the possible high CPU usage, run the nexthop recursive-lookup restrain disable command to disable BGP recursion suppression in case of next hop flapping.
Run quit
Return to the BGP view.
Run nexthop recursive-lookup restrain suppress-interval add-count-time hold-interval hold-count-time clear-interval clear-count-time
The intervals are configured for increasing, retaining, and clearing the penalty value for BGP recursion suppression in case of next hop flapping.
Run commit
The configuration is committed.

Checking the Configurations

After configuring BGP recursion suppression in case of next hop flapping, check the configurations.

Run the display bgp routing-table command to check BGP public network route information.
Run the display bgp vpnv4 routing-table command to check BGP VPNv4 and BGP VPN route information.