Special Considerations when Configuring VSRP Fast Start

Consider the following when configuring VSRP fast start:

• VSRP is sensitive to port status. When a port goes down, the VSRP instance lowers its priority based on the port up fraction. Since the VSRP fast start feature toggles port status by bringing ports down and up it can affect VSRP instances because their priorities get reduced when a port goes down. To avoid this, the VSRP fast start implementation keeps track of ports that it brings down and suppresses port down events for these ports.
• Once a VSRP restart port is brought up by a VSRP instance, other VSRP instances (in Master state) that have this port as a member do not go to forwarding immediately. This is a safety measure that is required to prevent transitory loops. This could happen if a peer VSRP node gets completely cut off from this node and assumed the Master state. In this case, where there are 2 VSRP instances that are in Master state and forwarding, the port comes up and starts forwarding immediately. This would cause a forwarding loop. To avoid this, the VSRP instance delays forwarding.