Concept Guide

Figure 129. Enhanced VLT
Congure Virtual Link Trunking
VLT requires that you enable the feature and then congure the same VLT domain, backup link, and VLT interconnect on both peer
switches.
Important Points to Remember
• 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, congure it before VLT. Refer to Congure Rapid Spanning Tree.
• If you include PVST on the system, congure it before VLT. Refer to PVST Conguration.
• 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 trac 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 oer may not be
forwarded by the ToR to the correct node. To avoid this issue, congure 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-channels to or from a
VLAN. You can manually add or remove a VLTi port-channel to a VLAN. In case a VLTi port-channel is manually removed from a VLAN,
it is added back to the VLAN after reload of the VLTi peers.
• Use the lacp ungroup member-independent command only if the system connects to nodes using bare metal provisioning
(BMP) to upgrade or boot from the network. Otherwise, when the member links ap, the links become independent switch ports and
forward the trac even before LACP is formed on that port.
• Ensure that you congure all port channels as hybrid ports and as untagged members of a VLAN where the LACP ungroup option is
applicable.
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Virtual Link Trunking (VLT)