Connectivity Guide

Virtual Link Trunking

Virtual Link Trunking (VLT) is a Layer 2 (L2) aggregate protocol between end devices such as servers connected to dierent network

devices. VLT reduces the role of Spanning Tree Protocols (STPs) by allowing link aggregation group (LAG) terminations on two separate

distributions or core switches.

VLT:

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

• Provides a loop-free topology

• Eliminates STP-blocked ports

• Optimizes using all available uplink bandwidth

• Guarantees fast convergence if either a link or device fails

• Enhances optimized forwarding with Virtual Router Redundancy Protocol (VRRP)

• Provides link-level resiliency

• Assures high availability

VLT provides L2 multipathing, creating redundancy through increased bandwidth, enabling multiple parallel paths between nodes and load-

balancing trac where alternative paths exist.

VLT presents a single logical L2 domain from the perspective of attached devices that have a virtual link trunk terminating on separate

nodes in the VLT domain. The two VLT nodes are independent Layer2/ Layer3 (L2/L3) switches for devices in the upstream network.

L2/L3 control plane protocols and system management features function normally in VLT mode.

VLT congurations must be identical on both sides of a trunk. External switches or servers with LACP see the VLT switches as a single

virtual switch.

VLT physical ports

802.1p, 802.1q, LLDP, ow control, port monitoring, and jumbo frames are supported on VLT physical ports.

System

management

protocols

All system management protocols are supported on VLT ports — SNMP, RMON, AAA, ACL, DNS, FTP, SSH,

syslog, NTP, RADIUS, SCP, and LLDP.

1034 Virtual Link Trunking