What is the function of the delay for LACP preemption

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When an Eth-Trunk interface in LACP mode goes Up and Down frequently due to unstable physical links, LACP goes Up and Down accordingly. As a result, services transmitted on the Eth-Trunk link are affected. After the LACP preemption delay is set, LACP negotiation is not performed during the delay period. The possibility of LACP flapping is reduced, and services will not be affected.

You can run the lacp preempt enable command to enable the LACP preemption function on the current Eth-Trunk interface and run the lacp preempt delay delay-time command to configure the preemption delay.

Other related questions:
Is it normal if the VRRP preemption delay configured on an AR router is different from actual delay
Is it normal if the VRRP preemption delay configured on an AR router is different from actual delay? It is normal. The backup-to-master conversion procedure for VRRP devices is as follows: Backup device: If the backup device receives packets with priority being 0 (lower than the priority of its own packets), the timer is set to Skew_time (offset time). If the packet priority is not 0, the packets are discarded and the backup device changes to the master state immediately. Master device: The master device sends VRRP advertisement packets regularly, and publicizes its configuration information (priority, for example) and working state in the VRRP group. Based on the VRRP packets, the backup device determines whether the master device works normally. - If the master device drops its master state (for example, it quits the backup group), it sends an advertisement packet with priority set to 0, to enable the backup device to change to the master state quickly without waiting for the timer specified by Master_Down_Interval to expire. This switchover time is referred to as the skew time, and is calculated based on the formula: �?56 - Backup device priority)/256 (unit: second). - If the master device encounters a network fault and cannot send an advertisement packet, the backup device will not know the status of the master device immediately and is notified of the fault until the timer specified by Master_Down_Interval expires. In this case, the backup device considers that the master device cannot work normally and switches over to the master state. The value of Master_Down_Interval is calculated based on the formula: 3 x Advertisement_Interval + Skew_time (unit: second). Note: In a performance-unstable network, network congestion may result in a backup device failure to receive packets from the master device within the time specified by Master_Down_Interval. In this case, the backup device will automatically switch over to the master state. If the packets from the master device arrive then, the device switches back to the backup state. This is likely to cause frequent switchover between VRRP devices. To relieve this phenomenon, a preemption delay can be configured to enable the backup device to wait for the preemption delay time after the timer specified by Master_Down_Interval expires. Before this relay time expires, the backup device will not switch over to the master state even if it does not receive an advertisement packet.

Does an Eth-Trunk support LACP priority preemption
An Eth-Trunk supports LACP priority preemption only in LACP mode. You can run the lacp preempt enable command to enable LACP priority preemption. In LACP mode, when an active link fails, the system selects the link with the highest priority from backup links to replace the faulty one. After the faulty link recovers and the priority of the link is higher than that of the backup one, if LACP priority preemption is enabled, the link with a high priority replaces the link with a low priority and switches to active. LACP priority preemption configuration at both ends of an Eth-Trunk must be the same.

Does a long preemption delay for the active firewall affect the failure response speed
No. When the active firewall fails, services are immediately switched to the standby firewall. After the original active firewall recovers, it must wait for the preemption delay before preempting. During the process, the standby firewall is working. Therefore, the long preemption delay of the active firewall does not affect the failure response speed.

Why does the active firewall require a longer preemption delay than that on the standby firewall
Preemption starts after the original active firewall recovers. If the preemption delay of the active firewall is too shorter than that on the standby firewall, the active firewall may switch status before the session entries on the standby firewall are completely synchronized to the active firewall. As a result, some services may be interrupted. Therefore, the active firewall requires a longer preemption delay. Preemption does not start after the standby firewall recovers. Therefore, preemption delay is meaningless for the standby firewall and you can use the default preemption delay.

Delay measurement
Path delay refers to the time from the source to the sink, which is measured using overheads. Delay measurement is used to measure the E2E bidirectional delay of ODUk signals. If ODUk SNCP protection is configured on the trail, the measurement result is the delay of the current working trail. The measurement process automatically inserts PM-layer delay measurement overhead bytes to the OTU board at the source end. The intermediate NEs transparently transmit the overhead bytes and the sink end loops back the overhead bytes. After the measurement is complete, the related configurations are automatically restored.

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