Configure Virtual Link TrunkingVLT requires that you enable the feature and then configure the same VLT domain, backup link, and VLTinterconnect on both peer switches.Important Points to Remember• 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 youdisable LACP on the VLTi.• Ensure that the spanning tree root bridge is at the Aggregation layer. If you enable RSTP on the VLTdevice, refer to RSTP and VLT for guidelines to avoid traffic loss.• If you reboot both VLT peers in BMP mode and the VLT LAGs are static, the DHCP server reply to theDHCP 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 supportedby 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. Afterrebooting, 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-restorecommand 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 avalue that allows sufficient time for all routes to establish adjacency and exchange all the L3 routesbetween the VLT peers before you enable the VLT ports.• Only use the lacp ungroup member-independent command if the system connects to nodesusing 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 asuntagged members of a VLAN. BMP uses untagged dynamic host configuration protocol (DHCP)packets to communicate with the DHCP server.• If the DHCP server is located on the ToR and the VLTi (ICL) is down due to a failed link when a VLTnode is rebooted in BMP mode, it is not able to reach the DHCP server, resulting in BMP failure.• If the source is connected to an orphan (non-spanned, non-VLT) port in a VLT peer, the receiver isconnected to a VLT (spanned) port-channel, and the VLT port-channel link between the VLT peerconnected to the source and TOR is down, traffic is duplicated due to route inconsistency betweenpeers. To avoid this scenario, Dell Networking recommends configuring both the source and thereceiver on a spanned VLT VLAN.• Bulk Sync happens only for Global IPv6 Neighbors; Link-local neighbor entries are not synced.• If all of the following conditions are true, MAC addresses may not be synced correctly:– VLT peers use VLT interconnect (VLTi)– Sticky MAC is enabled on an orphan port in the primary or secondary peer– MACs are currently inactiveIf this scenario occurs, use the clear mac-address-table sticky all command on the primaryor secondary peer to correctly sync the MAC addresses.• If static ARP is enabled on only one VLT peer, entries may be overwritten during bulk sync.• For multiple VLT LAGs configured on the same VLAN, if a host is learned on one VLT LAG and there isa station move between LAGs, the link local address redirects to the VLTi link on one of the peers. Ifthis occurs, clear the link local address that is redirecting to the VLTi link.Virtual Link Trunking (VLT) 927
