Concept Guide

• With peer routing, you need not use VRRP.
• You can use routing protocols in a VLT domain or between VLT domains (eVLT).
• VLT Proxy Gateway enables one VLT domain to act as the default gateway for its peer VLT domain in an eVLT topology.
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.
• BMP uses untagged dynamic host conguration protocol (DHCP) packets to communicate with the DHCP server.
• o disable this feature on VLT and port channels, use no lacp ungroup member-independent {vlt | port-channel}
command under the conguration mode.
• 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 sucient 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 congure all port channels where LACP ungroup is applicable as hybrid ports and as untagged members of a VLAN.
BMP uses untagged dynamic host conguration 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 VLT node 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 is connected to a VLT (spanned) port-
channel, and the VLT port-channel link between the VLT peer connected to the source and ToR is down, trac is duplicated due to
route inconsistency between peers. To avoid this scenario, Dell EMC Networking recommends conguring both the source and the
receiver 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)
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Virtual Link Trunking (VLT)