• 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 selectVLANs.• VLT peer switches operate as separate chassis with independent control and data planes fordevices attached to non-VLT ports.• Port-channel link aggregation (LAG) across the ports in the VLT interconnect is required; individualports 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 usingVLTi 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 VLTinterconnect on an egress port such as a VLT LAG. MAC addresses are the same on both VLT peernodes.• 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 domainin which you did not configure a backup link, the switch’s role displays in the show vlt briefcommand 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 discoveryprotocol (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 thefollowing configured information is true on both peer switches:• the VLT-system MAC address (if configured) matches.• the VLT unit-id (if configured) is not identical.NOTE: If the VLT-system MAC address or VLT unit-id is not configured on both VLT peerswitches, VLT automatically sets the default VLT-system MAC address and unit-id oneach peer.• If the link between the VLT peer switches is established, changing the VLT-system MAC address orthe VLT unit-id causes the link between the VLT peer switches to become disabled. However,removing the VLT-system MAC address or the VLT unit-id may disable the VLT ports if you happento configure the unit ID or system MAC address on only one VLT peer at any time.• If the link between VLT peer switches is established, any change to the VLT-system MAC addressor unit-id fails if the changes made create a mismatch by causing the VLT unit-ID to be the sameon both peers and/or the VLT-system MAC address does not match on both peers.• If you replace a VLT peer node, pre-configure the switch with the VLT-system MAC address, unit-id, and other VLT parameters (if applicable) before connecting it to the existing VLT peer switchusing the VLTi connection.• VLT backup link• In the backup link between peer switches, heartbeat messages are exchanged between the twochassis for health checks. The default time interval between heartbeat messages over the backuplink is 1 second. You can configure this interval. The range is from 1 to 5 seconds. DSCP markingon heartbeat messages is CS6.• In order that the chassis backup link does not share the same physical path as the interconnecttrunk, Dell Networking recommends using the management ports on the chassis and traverse anout-of-band management network. The backup link can use user ports, but not the same ports theinterconnect trunk uses.• The chassis backup link does not carry control plane information or data traffic. Its use is restrictedto health checks only.Virtual Link Trunking (VLT) 1169
