nexthop recursive-lookup non-critical-event delay

Function

The nexthop recursive-lookup non-critical-event delay command enables a device to respond to non-urgent BGP next-hop iteration changes after a specified delay time.

The undo nexthop recursive-lookup non-critical-event delay command enables a device to immediately respond to non-urgent BGP next-hop iteration changes.

By default, a device immediately responds to non-urgent BGP next-hop iteration changes.

Format

nexthop recursive-lookup non-critical-event delay [ delay-time ]

undo nexthop recursive-lookup non-critical-event delay

Parameters

Parameter	Description	Value
delay-time	Specifies the delay time.	The value is an integer that ranges from 1 to 100, in seconds. The default value is 5.

Views

BGP view, BGP-IPv4 unicast address family view, or BGP-VPN instance IPv4 address family view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

If repeated iteration 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 next-hop iteration changes after a specified delay time. The iteration results are as follows:

Urgent iteration result change: The iterated 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 is iterated. As a result, traffic is interrupted.
Non-urgent iteration result change: The iterated 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 is iterated is changed, traffic keeps traveling over the BGP route.

To delay a response to the non-urgent iteration change, run the nexthop recursive-lookup non-critical-event delay command, not the nexthop recursive-lookup delay command.

Configuration Impact

After the nexthop recursive-lookup delay command is run, the device delays responses to all next-hop iteration changes. After the nexthop recursive-lookup non-critical-event delay command is run, the device delays responses only to non-urgent BGP next-hop iteration changes. If both commands are run, the nexthop recursive-lookup non-critical-event delay command takes precedence over the nexthop recursive-lookup non-critical-event delay command. Table 1 provides examples of the two commands.

**Table 1** Functions and their descriptions
Example	Description
[HUAWEI-bgp] nexthop recursive-lookup delay	The device responds to all BGP next-hop iteration changes after a 5-second delay.
[HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay	The device immediately responds to urgent BGP next-hop iteration changes and responds to non-urgent BGP next-hop iteration changes after a 5-second delay.
[HUAWEI-bgp] nexthop recursive-lookup delay 3	The device responds to all BGP next-hop iteration changes after a 3-second delay.
[HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay 6	The device immediately responds to urgent BGP next-hop iteration changes and responds to non-urgent BGP next-hop iteration changes after a 6-second delay.
[HUAWEI-bgp] nexthop recursive-lookup delay [HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay	The device responds to all BGP next-hop iteration changes after a 5-second delay.
[HUAWEI-bgp] nexthop recursive-lookup delay 3 [HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay	The device responds to urgent BGP next-hop iteration changes after a 3-second delay and responds to non-urgent BGP next-hop iteration changes after a 5-second delay.
[HUAWEI-bgp] nexthop recursive-lookup delay 3 [HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay 6	The device responds to urgent BGP next-hop iteration changes after a 3-second delay and responds to non-urgent BGP next-hop iteration changes after a 6-second delay.
[HUAWEI-bgp] nexthop recursive-lookup delay [HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay 6	The device responds to urgent BGP next-hop iteration changes after a 5-second delay and responds to non-urgent BGP next-hop iteration changes after a 6-second delay.

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.

Example

# Enable the device to respond to non-urgent BGP next-hop iteration changes after a 10-second delay.

<HUAWEI> system-view

[HUAWEI] bgp 100

[HUAWEI-bgp] nexthop recursive-lookup non-critical-event delay 10