Administrator Guide

between the two VLT chassis. IGMP and VLT configurations must be identical on both sides of the trunk to ensure the same behavior on
both sides.
The following example shows how VLT is deployed. The switches appear as a single virtual switch from the point of view of the switch or
server supporting link aggregation control protocol (LACP).
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 connectivity between the 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.
• VLT domain — This domain includes both the VLT peer devices, VLT interconnect, and all of the port channels in the VLT connected
to the attached devices. It is also associated to the configuration mode that you must use to assign VLT global parameters.
• VLT peer device — One of a pair of devices that are connected with the special port channel known as the VLT interconnect (VLTi).
• Enhanced VLT (eVLT) — Combining two VLT domains. eVLT can operate in layer 2 and layer 3 modes. eVLT is also known as
mVLT.
VLT peer switches have independent management planes. A VLT interconnect between the VLT chassis maintains synchronization of
L2/L3 control planes across the two VLT peer switches.
A separate backup link maintains heartbeat messages across an out-of-band (OOB) management network. The backup link ensures that
node failure conditions are correctly detected and are not confused with failures of the VLT interconnect. VLT ensures that local traffic on
a chassis does not traverse the VLTi and takes the shortest path to the destination via directly attached links.
The following is a summary of VLT and its functions:
• End devices (such as switches, servers, and so on) connected to a VLT domain consider the two VLT peers as a single logical switch.
• Although VLT does not require spanning tree protocols, Dell EMC Networking recommends enabling RSTP before configuring VLT to
avoid possible loops from forming due to incorrect configuration.
• You can connect two VLT domains to create an eVLT topology.
• You can use eVLT as layer 2.
• Peer routing enables one VLT node to act as the default gateway for its VLT peer within a VLT domain.
• With peer routing, you need not use VRRP.
• You can use routing protocols in a VLT domain or between VLT domains (eVLT).
• VLT Proxy Gateway enables one VLT domain to act as the default gateway for its peer VLT domain in an eVLT topology.
Layer-2 Traffic in VLT Domains
In a VLT domain, the MAC address of any host connected to the VLT peers is synchronized between the VLT nodes. In the following
example, VLAN 10 is spanned across three VLT domains.
Figure 130. Layer-2 Traffic in VLT Domains
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Virtual Link Trunking (VLT)