– 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 (OS)
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 sixteen 10G or 40G
ports are supported. A combination of 10G and 40G ports are 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.
– IGMP state information is synchronized between the VLT chassis over the VLT interconnect.
– The traffic transmitted over VLT interconnect is prioritized, and allows you to configure the traffic
class-to-queue assignment.
– 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.
– When you change the default VLAN ID on a VLT peer switch, the VLT interconnect may flap.
– In a VLT domain, the following software features are supported on VLTi: link layer discovery
protocol (LLDP), flow control, port monitoring, jumbo frames, and data center bridging (DCB).
– When you enable the VLTi link, the link between the VLT peer switches is established if the
following configured information is true on both peer switches:
Virtual Link Trunking (VLT)
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