Reference Guide

Virtual Link Trunking (VLT) | 949

Virtual Link Trunking (VLT)

Virtual Link Trunking (VLT) is supported on the S5000 switch.

This chapter covers the following information:

• Overview

• VLT Terminology

• Configuring Virtual Link Trunking

• RSTP Configuration

• Verifying a VLT Configuration

• Sample Configuration: Virtual Link Trunking

• Troubleshooting VLT

• Reconfiguring Stacked Switches as VLT

Overview

Virtual link trunking (VLT) allows physical links between two chassis to appear as a single virtual link to

the network core or other switches such as Edge, Access or ToR. VLT reduces the role of Spanning Tree

protocols by allowing LAG terminations on two separate distribution or core switches, and by supporting a

loop free topology. (A Spanning Tree protocol is still needed to prevent the initial loop that may occur prior

to VLT being established. 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.) VLT provides Layer 2 multipathing,

creating redundancy through increased bandwidth, enabling multiple parallel paths between nodes and

load-balancing traffic where alternative paths exist.

Virtual link trunking offers the following benefits:

• Allows a single device to use a LAG across two upstream devices

• Eliminates Spanning Tree Protocol (STP) blocked ports

• Provides a loop-free topology

• Uses all available uplink bandwidth

• Provides fast convergence if either the link or a device fails

• Optimized forwarding with VRRP

• Provides link-level resiliency

• Assures high availability