Addendum

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) configuration creates a port channel between two VLT domains by allowing two
different VLT domains, using different 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 configuration supports a maximum of four units, 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.
Figure 4. Enhanced VLT
VLT Terminology
The following are key VLT terms.
• Virtual link trunk (VLT) — The combined port channel between an attached device and the VLT peer
switches.
• VLT backup link — The backup link monitors the vitality of VLT peer switches. The backup link sends
configurable, periodic keep alive messages between the VLT peer switches.
• VLT interconnect (VLTi) — The link used to synchronize states between the VLT peer switches. Both
ends must be on 10G or 40G interfaces.
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Virtual Link Trunking (VLT)