Figure 123. 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 trac where alternate paths exist.
L2/L3 control plane protocols and system management features function normally in VLT mode. Features such as VRRP and internet group
management protocol (IGMP) snooping require state information coordination between the two VLT chassis. The IGMP and VLT
congurations must be identical on both sides of the trunk to ensure the same behavior on both sides.
The following example shows how VLT is deployed. The switches appear as a single virtual switch from the point of view of the switch or
server supporting link aggregation control protocol (LACP).
Virtual Link Trunking (VLT)
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