The nexthop recursive-lookup delay command configures a delay in responding to changes in the next hop recursion result.
The undo nexthop recursive-lookup delay command restores the default configuration.
The nexthop recursive-lookup non-critical-event delay command configures a delay in responding to non-critical next-hop recursion changes.
The undo nexthop recursive-lookup non-critical-event delay command restores the default configuration.
By default, a device immediately responds to BGP recursion changes.
| Parameter | Description | Value |
|---|---|---|
| delay-time |
Specifies the delay in responding to recursion changes. |
The value is an integer that ranges from 1 to 100, in seconds. By default, the value is 5s. |
| nonCrit-delay-time |
Indicates the delay in responding to non-critical recursion changes. |
The value is an integer ranging from 0 to 100, in seconds. The default value is 10. |
Usage Scenario
If repeated recursion causes the BGP next hop to frequently change on a device, the device frequently selects and advertises routes. To prevent unwanted re-routing and route advertisement, run the nexthop recursive-lookup delay command to enable the device to respond to BGP recursion changes after a specified delay time. The recursion results are as follows:Critical recursion result change: The recursive next hop is changed, and BGP route reachability is also changed. For example, if a fault occurs on a network, a device finds no next-hop route or tunnel to which a BGP route recurses. As a result, traffic is interrupted.Non-critical recursion result change: The recursive next hop is changed, and BGP route reachability is not affected. For example, after the interface or type of a tunnel to which the next hop of a BGP route recurses is changed, traffic keeps traveling over the BGP route.
Configuration Impact
After the nexthop recursive-lookup delay command is run, the device delays responses to all recursion changes. After the nexthop recursive-lookup non-critical-event delay command is run, the device delays responses only to non-critical BGP recursion changes. If both commands are run, the nexthop recursive-lookup non-critical-event delay command takes precedence over the nexthop recursive-lookup delay command. Table Functions and their descriptions provides examples of the two commands.
Precautions
The delay time specified in the nexthop recursive-lookup non-critical-event delay command must be greater than or equal to that specified in the nexthop recursive-lookup delay command if both commands are run.The BGP next hop delayed response applies to a scenario where the next hop has multiple links to reach the same destination. If there is only one link between the next hop and the destination, configuring the BGP next hop delayed response may cause heavier traffic loss when the link fails because link switching is impossible.