Reference Guide

846 | Virtual Link Trunking (VLT)
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Figure 46-1. Virtual Link Trunking
VLT peer devices have independent management planes. A chassis interconnect trunk between the VLT
chassis maintains synchronization of L2/L3 control planes across the two VLT peers. The chassis
interconnect trunk uses 10GE or 40GE user ports on the chassis.
A separate backup link maintains heartbeat messages across an out-of-band management network. The
backup link ensures that node failure conditions are correctly detected and are not confused with failures of
the chassis interconnect trunk. VLT ensures that local traffic on a chassis does not traverse the chassis
interconnect trunk and takes the shortest path to the destination via directly attached links.
Virtual link trunking offers the following benefits:
• Allows a single device to use a LAG across two upstream devices
• 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
VLT Domain
S4810
S4810
Chassis
Chassis
Interconnect
Trunk
Backup
Link
Virtual Link Trunk
Switch or Server that supports LACP (802.1ad)
O
ut-o
f
-Band
M
anagement
Ne
tw
o
r
k
Backup
Link