VRRP and Spanning Tree

The switch can use one of two spanning tree protocols: Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP).

VRRP protects clients and servers from link or aggregation switch failures. Configure the network to limit the amount of time a link is out of service during VRRP convergence.

The following figure shows two possible configurations of VRRP and spanning tree; configuration A is optimal and configuration B is not.

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VRRP and STG configurations

In this figure, configuration A is optimal because VRRP convergence occurs within 2 to 3 seconds. In configuration A, three spanning tree instances exist and VRRP runs on the link between the two routers. Spanning tree instance 2 exists on the link between the two routers, which separates the link between the two routers from the spanning tree instances found on the other devices. All uplinks are active.

In configuration B, VRRP convergence takes between 30 and 45 seconds because it depends on spanning tree convergence. After initial convergence, spanning tree blocks one link (an uplink), so only one uplink is used. If an error occurs on the uplink, spanning tree reconverges, which can take up to 45 seconds. After spanning tree reconvergence, VRRP can take a few more seconds to fail over.