(Optional) Configuring VRRP6 Stability Functions

To help a VRRP6 group work stably, enable the preemption function, set a preemption delay, and specify an interval at which VRRP6 Advertisement packets are sent. The configuration can minimize impact of network flapping resulted from frequent master/backup VRRP6 switchovers on data forwarding.

Context

A VRRP6 group performs a master/backup switchover if the master device fails or a network is busy. After the master device or network communication recovers, a new master device is selected based on device priorities.

If a network frequently flaps, service traffic may fail to be forwarded. To resolve this issue, configure VRRP6 stability functions to improve VRRP6 group stability, minimizing network interruptions or packet loss resulted from frequent master/backup VRRP6 switchovers. Table 1 describes VRRP6 stability functions.

**Table 1** VRRP6 stability functions
Function Item	Description
Setting a preemption delay for a device in a VRRP6 group	Frequent master/backup switchovers on an unstable network may cause double master devices to coexist or hosts to learn an incorrect master MAC address. To maintain the stable master/backup status, perform the following configurations: Configure immediate preemption for backup devices. In immediate preemption mode, a backup device immediately preempts the Master state after the master device fails. The preemption delay is 0s. This setting minimizes the service interruption duration. Configure delayed preemption for the master device. In delayed preemption mode, the master device preempts the Master state a specified preemption delay after the master device recovers. During the preemption delay, other services (such as route convergence) are restored. The preemption delay helps minimize packet loss ratios.
Setting the interval at which VRRP6 Advertisement packets are sent	If a backup device does not receive a VRRP6 Advertisement packet within a specified timeout period due to heavy network traffic or timer differences, a master/backup VRRP6 switchover is performed. To prevent this situation, configure a large interval at which the master device sends VRRP6 Advertisement packets.
Setting a status recovery delay for a VRRP6 group	If the status of the interface on which a VRRP6 group resides frequently changes, the VRRP6 group frequently flaps. To prevent this situation, set a status recovery delay for the VRRP6 group. A VRRP6 group responds to a VRRP6 interface Up event only after a specified status recovery delay. The status recovery delay helps prevent VRRP6 status flapping caused by frequent interface status changes.

Procedure

Set a preemption delay for a device in a VRRP6 group.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The view of the interface on which the VRRP6 group is configured is displayed.
3. Run vrrp6 vrid virtual-router-id preempt-mode timer delay delay-time
  A preemption delay is set for the device in the VRRP6 group.
  
  When a VRRP6 group works in immediate preemption mode, a backup device in the group can immediately preempt the Master state when its priority is higher than that of the master device.
  
  You can run the vrrp6 vrid virtual-router-id preempt-mode disable command to configure the non-preemption mode for devices in a VRRP6 group. When a VRRP6 group works in non-preemption mode, another backup device cannot preempt the Master state so long as the master device is working properly.
  
  A preemption delay is a period of time during which a backup device waits to preempt the Master state. When an IP address owner recovers from a fault, it immediately preempts the Master state. Therefore, the preemption delay is meaningless for an IP address owner. If a preemption delay needs to be configured for a VRRP6 group, do not configure the master device in the group as an IP address owner.
4. Run commit
  The configuration is committed.
Set the interval at which VRRP6 Advertisement packets are sent.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The view of the interface on which the VRRP6 group is configured is displayed.
3. Run vrrp6 vrid virtual-router-id timer advertise advertise-interval
  The interval at which VRRP6 Advertisement packets are sent is set.
4. (Optional) Run vrrp6 vrid virtual-router-id timer advertise millisecond millisecond-interval
  The interval at which VRRP6 Advertisement packets are sent is set.
5. Run commit
  The configuration is committed.
Set a status recovery delay for a VRRP6 group.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The view of the interface on which the VRRP6 group is configured is displayed.
3. Run vrrp6 recover-delay delay-value
  A status recovery delay is set for the VRRP6 group.
4. Run commit
  The configuration is committed.