Administrator Guide

Overview
In a traditional switched topology as shown below, spanning tree protocols (STPs) are used to block one or more links to
prevent loops in the network. Although loops are prevented, bandwidth of all links is not effectively utilized by the connected
devices.
Figure 153. Traditional switched topology
VLT not only overcomes this caveat, but also provides a multipath to the connected devices. In the example shown below, the
two physical VLT peers appear as a single logical device to the connected devices. As the connected devices consider the VLT
peers as a single switch, VLT eliminates STP-blocked ports. However, the two VLT devices are independent Layer2/Layer3
(L2/L3) switches for devices in the upstream network.
Figure 154. VLT providing multipath
VLT reduces the role of spanning tree protocols (STPs) by allowing link aggregation group (LAG) terminations on two separate
distribution or core switches and supporting a loop-free topology.
To prevent the initial loop that may occur prior to VLT being established, use a spanning tree protocol. After VLT is established,
you may use rapid spanning tree protocol (RSTP) to prevent loops from forming with new links that are incorrectly connected
and outside the VLT domain.
VLT provides Layer 2 multipathing, creating redundancy through increased bandwidth, enabling multiple parallel paths between
nodes, and load-balancing traffic where alternate paths exist.
Virtual Link Trunking (VLT)
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