Users Guide

Figure 129. VLT on S4820T Switches
VLT on Core Switches
Uplinks from servers to the access layer and from access layer to the aggregation layer are bundled in LAG groups with end-to-end
Layer 2 multipathing. This set up requires “horizontal” stacking at the access layer and VLT at the aggregation layer such that all the
uplinks from servers to access and access to aggregation are in Active-Active Load Sharing mode. This example provides the highest
form of resiliency, scaling, and load balancing in data center switching networks.
The following example shows stacking at the access, VLT in aggregation, and Layer 3 at the core.
The aggregation layer is mostly in the L2/L3 switching/routing layer. For better resiliency in the aggregation, Dell Networking
recommends running the internal gateway protocol (IGP) on the VLTi VLAN to synchronize the L3 routing table across the two
nodes on a VLT system.
Enhanced VLT
An enhanced VLT (eVLT) conguration creates a port channel between two VLT domains by allowing two dierent VLT domains,
using dierent VLT domain ID numbers, connected by a standard link aggregation control protocol (LACP) LAG to form a loop-free
Layer 2 topology in the aggregation layer.
This conguration supports a maximum of four switches, increasing the number of available ports and allowing for dual redundancy
of the VLT. The following example shows how the core/aggregation port density in the Layer 2 topology is increased using eVLT. For
inter-VLAN routing and other Layer 3 routing, you need a separate Layer 3 router.
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Virtual Link Trunking (VLT)