Administrator Guide

● 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. Both ends must be on
10G or 40G interfaces.
● 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 139. Layer-2 Traffic in VLT Domains
If Host 1 from a VLT domain sends a frame to Host 2 in another VLT domain, the frame can use any link shown to reach Host 2.
MAC synchronization between VLT peers handles the traffic flow even if it is hashed and forwarded through the other member
of the port-channel.
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Virtual Link Trunking (VLT)