How to configure Multi-box VRRP

Products

• XOS

Issue/Introduction

This article discusses VRRP behavior with 3 or more chassis in VRRP cluster.

Cause

When configuring VRRP with 3 or more chassis, VRRP failover randomly occurs between the other chassis and not to the next-highest-priority one.

For example:

Chassis 1:

vrrp failover-group XXX failover-group-id X

  priority 250

Chassis 2:

vrrp failover-group XXX failover-group-id X

  priority 200

Chassis 3:

vrrp failover-group XXX failover-group-id X

  priority 150

Failover from Chassis 1 will be to either Chassis 2 or Chassis 3.

Resolution

VRRP failover uses a "first to answer" mechanism.
The chassis that answers firts will become "master" for the failover group after a failover.

To ensure that failover takes place by priority, enable preemption on chassis to ensure that the next priority chassis becomes master.
Even if another chassis answers first, preemption will ensure a failover to the highest priority chassis.


Chassis 1:

vrrp failover-group XXX failover-group-id X

  preemption
  priority 250

Chassis 2:

vrrp failover-group XXX failover-group-id X

  preemption
  priority 200

Chassis 3:

vrrp failover-group XXX failover-group-id X

  preemption
  priority 150

To reduce automatic failbacks, you can enable preemption on Chassis 2 only.
When Chassis 1 goes down, even if Chassis 3 is the first to answer, preemption will ensure that Chassis 2 becomes master.

When the problem that caused a failover from Chassis 1 is rectified, no failback will occur because preemption is not configured on Chassis 1.

However, in this case, failing back from Chassis 2 will be on "first to answer" mechanism.