Reference Guide

Configuration Notes
When you configure VLT, the following conditions apply.
• VLT domain
– A VLT domain supports two chassis members, which appear as a single logical device to network
access devices connected to VLT ports through a port channel.
– A VLT domain consists of the two core chassis, the interconnect trunk, backup link, and the LAG
members connected to attached devices.
– Each VLT domain has a unique MAC address that you create or VLT creates automatically.
– ARP tables are synchronized between the VLT peer nodes.
– VLT peer switches operate as separate chassis with independent control and data planes for devices
attached on non-VLT ports.
– One chassis in the VLT domain is assigned a primary role; the other chassis takes the secondary role.
The primary and secondary roles are required for scenarios when connectivity between the chassis is
lost. VLT assigns the primary chassis role according to the lowest MAC address. You can configure the
primary role.
– In a VLT domain, the peer switches must run the same Dell Networking operating system (FTOS)
software version.
– Separately configure each VLT peer switch with the same VLT domain ID and the VLT version. If the
system detects mismatches between VLT peer switches in the VLT domain ID or VLT version, the VLT
Interconnect (VLTi) does not activate. To find the reason for the VLTi being down, use the show vlt
statistics
command to verify that there are mismatch errors, then use the show vlt brief
command on each VLT peer to view the VLT version on the peer switch. If the VLT version is more than
one release different from the current version in use, the VLTi does not activate.
– The chassis members in a VLT domain support connection to orphan hosts and switches that are not
connected to both switches in the VLT core.
• VLT interconnect (VLTi)
– The VLT interconnect must consist of either 10G or 40G ports. A maximum of eight 10G or four 40G ports
is supported. A combination of 10G and 40G ports is not supported.
– A VLT interconnect over 1G ports is not supported.
– The port channel must be in Default mode (not Switchport mode) to have VLTi recognize it.
– The system automatically includes the required VLANs in VLTi. You do not need to manually select
VLANs.
– VLT peer switches operate as separate chassis with independent control and data planes for devices
attached to non-VLT ports.
– Port-channel link aggregation (LAG) across the ports in the VLT interconnect is required; individual ports
are not supported. Dell Networking strongly recommends configuring a static LAG for VLTi.
– The VLT interconnect synchronizes L2 and L3 control-plane information across the two chassis.
– The VLT interconnect is used for data traffic only when there is a link failure that requires using VLTi in
order for data packets to reach their final destination.
– Unknown, multicast, and broadcast traffic can be flooded across the VLT interconnect.
– MAC addresses for VLANs configured across VLT peer chassis are synchronized over the VLT
interconnect on an egress port such as a VLT LAG. MAC addresses are the same on both VLT peer
nodes.
– ARP entries configured across the VLTi are the same on both VLT peer nodes.
– If you shut down the port channel used in the VLT interconnect on a peer switch in a VLT domain in
which you did not configure a backup link, the switch’s role displays in the show vlt brief
command output as Primary instead of Standalone.
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