Users Guide

• by allowing LAG terminations on two separate distribution or core switches

• by supporting a loop-free topology, similar to how STP prevents any initial loops that may occur prior

to VLT being established

NOTE: After VLT is established, RSTP may be used to prevent loops from forming with new links that

are incorrectly connected and outside the VLT domain.

For information about VLT, refer to the Dell Networking Configuration Guide for the S4810, S6000, or the

Z9000, or refer to Selecting a Layer 2 and Layer 3 with Resiliency (Routed VLT) Fabric Design.

NOTE:

Dell Networking recommends that you do not enable stacking and VLT simultaneously.

If both are enabled at the same time, unexpected behavior occurs.

Multidomain VLT

A multidomain VLT (mVLT) configuration connects two different VLT domains in a standard Link

Aggregation Control protocol (LACP) LAG to form a loop-free Layer 2 topology in the aggregation layer.

This configuration supports up to four units, increasing the number of available ports and enabling dual

redundancy for VLT. For more information about mVLT deployments, refer to Selecting a Layer 2 VLT and

Layer 3 with Resiliency (Routed VLT) Fabric Design.

VLT Terminology

• Virtual link trunk (VLT) — The combined port channel between an attached device and the VLT peer

switches.

• VLT backup link — The backup link that monitors the health of VLT peer switches. The backup link

sends configurable periodic messages (also known as keep-alive messages) between VLT peer

switches.

• VLT interconnect (VLTi) — The link used to synchronize states between the VLT peer switches. Both

ends of the link must use 10 Gb or 40 Gb interfaces.

• VLT domain — Includes both VLT peer devices, the VLT interconnect, and all port channels

connected to the attached VLT devices. It is also associated with the configuration mode used to

assign VLT global parameters.

• VLT peer device — One of a pair of devices that are connected with to the port channel specified as

the VLTi.

VLT Fabric Terminology

The following terms are unique to the design and deployment of a Layer 2 VLT fabric.

• Core — A switch that connects to aggregation switches. The role of the core is to provide an

interconnect to all the aggregation switches. All ports on the core switch connect to the aggregation

switches and racks.

• Access — A switch that connects switch, servers, storage devices, or top-of-rack (TOR) elements. The

role of the access switch is to provide connectivity to the fabric. The access switch connects to all of

aggregation switches above it in the fabric.

• Aggregation — A switch that connects to access switches. The role of the aggregation layer is to

provide an interconnect to all the access switches. All the ports on the aggregation switches are used

to connect the access, various racks together. The aggregation switch provides redundancy.

• Edge ports — The uplinks on the aggregation and downlinks on the access.

Supported Fabric Types