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S12700 V200R013C00 Configuration Guide - Reliability

This document describes the configurations of Reliability, including BFD Configuration, VRRP Configuration, NSR Configuration, DLDP Configuration, Smart Link and Monitor Link Configuration, MAC Swap Loopback Configuration, EFM Configuration, CFM Configuration, Y.1731 Configuration.

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VRRP Smooth Switching

VRRP Smooth Switching

When an active/standby switchover occurs on the master equipped with dual MPUs in a VRRP group, the master may not send VRRP packets during the switching period. The backup then assumes the master role because it does not receive VRRP Advertisement packets after the Master_Down_Interval timer expires. In preemption mode, after the original master completes the active/standby switchover, it detects that it has a higher priority than the new master and preempts to be the master again. During this process, services are switched twice, causing unstable service transmission.

VRRP smooth switching can be enabled on the master to prevent service disruption during an active/standby switchover. During VRRP smooth switching, the master works with the backup to ensure smooth service transmission.
  1. Before VRRP smooth switching, the backup must be enabled to learn the interval for sending VRRP Advertisement packets. The backup receives a VRRP Advertisement packet from the master and checks the interval in the packet. If the interval in the packet is different from the locally configured interval, the backup changes its own interval to the interval in the received packet.
  2. When an active/standby switchover of the MPU on the master is started, the master will save the current interval at which VRRP Advertisement packets are sent and adjust the interval of smooth VRRP switching (the interval is larger than the value before the switchover). During smooth VRRP switching, the master sends VRRP Advertisement packets at the new interval.
  3. When the backup receives the VRRP Advertisement packet, it changes its own interval to the new interval in the packet.
  4. After the switchover is complete, the master restores its original interval and sends a VRRP Advertisement packet at the new interval. The backup learns the interval after receiving the packet.
  • During VRRP smooth switching, the learning function takes precedence over the preemption function. If the interval and the priority carried in the received packet are different from the current interval and lower than the configured priority, respectively, the learning function takes effect and the timer is reset.

  • VRRP smooth switching also depends on the system. If the system is busy due to the switchover and cannot schedule tasks of the VRRP module, VRRP smooth switching cannot take effect.

Updated: 2019-04-08

Document ID: EDOC1100065654

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