Administrator Guide

Figure 131. Enhanced VLT
Configure Virtual Link Trunking
VLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLT interconnect on both
peer switches.
Important Points to Remember
WARNING:
Do not add any VLANs to the VLT Interconnect. The VLTi interface manages VLAN tagged/untagged
traffic automatically between peers. Manually adding any VLAN configuration has been shown to disrupt traffic
flow. If a VLAN configuration has been added to the VLTi, the recommended recovery procedure is as follows for
both VLT members:
1. Remove the VLAN configuration from the interface
2. Save the configuration
3. Reload the VLT member
● You cannot enable stacking simultaneously with VLT. If you enable both at the same time, unexpected behavior can occur.
● VLT port channel interfaces must be switch ports.
● If you include RSTP on the system, configure it before VLT. Refer to Configure Rapid Spanning Tree.
● If you include PVST on the system, configure it before VLT.
● Dell EMC Networking strongly recommends that the VLTi (VLT interconnect) be a static LAG and that you disable LACP on
the VLTi.
● Ensure that the spanning tree root bridge is at the Aggregation layer. Refer to RSTP and VLT for guidelines to avoid traffic
loss, if you enable RSTP on the VLT device.
● If you reboot both VLT peers in BMP mode with static VLT LAGs, the DHCP server reply to the DHCP discover offer may
not be forwarded by the ToR to the correct node. To avoid this issue, configure the VLT LAGs to the ToR and the ToR port
channel to the VLT peers with LACP.
● If supported by the ToR, enable the lacp-ungroup feature on the ToR using the lacp ungroup member-independent
port-channel command. If the lacp-ungroup feature is not supported on the ToR, reboot the VLT peers one at a time.
After rebooting, verify that VLTi (ICL) is active before attempting DHCP connectivity.
● When a VLAN is created on VLTi peers, the VLTi port-channel is added automatically to the VLAN, whether the vlan have
members or not. A VLAN creation or deletion message from the VLT peer is the trigger for adding or removing VLTi port-
Virtual Link Trunking (VLT)
895