Users Guide

Figure 126. 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
• You cannot enable stacking simultaneously with VLT. If you enable both at the same time, unexpected behavior occurs.
• 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. Refer to PVST Configuration.
• Dell 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 and the VLT LAGs are static, the DHCP server reply to the DHCP discover offer may not
be forwarded by the ToR to the correct node. To avoid this scenario, 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 you enable IGMP snooping on the VLT peers, ensure the value of the delay-restore command is not less than the query
interval.
• When you enable Layer 3 routing protocols on VLT peers, make sure the delay-restore timer is set to a value that allows sufficient time
for all routes to establish adjacency and exchange all the L3 routes between the VLT peers before you enable the VLT ports.
• Only use the lacp ungroup member-independent command if the system connects to nodes using bare metal provisioning
(BMP) to upgrade or boot from the network.
• Ensure that you configure all port channels where LACP ungroup is applicable as hybrid ports and as untagged members of a VLAN.
BMP uses untagged dynamic host configuration protocol (DHCP) packets to communicate with the DHCP server.
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Virtual Link Trunking (VLT)