Administrator Guide

• VLT is not supported on an S5000 congured for FCoE transit or NPIV proxy gateway.
• VLT port channel interfaces must be switch ports.
• If you include RSTP on the system, congure it before VLT. Refer to Conguring Rapid Spanning Tree.
• 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. If you enable RSTP on the VLT device, refer to RSTP and VLT for
guidelines to avoid trac loss.
• If you reboot both VLT peers in BMP mode and the VLT LAGs are static, the DHCP server reply to the DHCP discover oer may not be
forwarded by the ToR to the correct node. To avoid this scenario, 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 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.
Conguration Notes
When you congure VLT, the following conditions apply.
• VLT domain
• A VLT domain supports two chassis members, which appear as a single logical device to network access devices connected to VLT
ports through a port channel.
• A VLT domain consists of the two core chassis, the interconnect trunk, backup link, and the LAG members connected to attached
devices.
• Each VLT domain has a unique MAC address that you create or VLT creates automatically.
• ARP tables are synchronized between the VLT peer nodes.
• VLT peer switches operate as separate chassis with independent control and data planes for devices attached on non-VLT ports.
• One chassis in the VLT domain is assigned a primary role; the other chassis takes the secondary role. The primary and secondary
roles are required for scenarios when connectivity between the chassis is lost. VLT assigns the primary chassis role according to the
lowest MAC address. You can congure the primary role.
• In a VLT domain, the peer switches must run the same Dell Networking OS software version.
• Separately congure each VLT peer switch with the same VLT domain ID and the VLT version. If the system detects mismatches
between VLT peer switches in the VLT domain ID or VLT version, the VLT Interconnect (VLTi) does not activate. To nd the reason
for the VLTi being down, use the show vlt statistics command to verify that there are mismatch errors, then use the show
vlt brief command on each VLT peer to view the VLT version on the peer switch. If the VLT version is more than one release
dierent from the current version in use, the VLTi does not activate.
• The chassis members in a VLT domain support connection to orphan hosts and switches that are not connected to both switches in
the VLT core.
• VLT interconnect (VLTi)
• The VLT interconnect must consist of either 10 GbE or 40 GbE ports. A maximum of eight 10 GbE or four 40 GbE ports is
supported. A combination of 10 GbE and 40 GbE ports is not supported.
• A VLT interconnect over 1G ports is not supported.
• The port channel must be in Default mode (not Switchport mode) to have VLTi recognize it.
• The system automatically includes the required VLANs in VLTi. You do not need to manually select VLANs.
• VLT peer switches operate as separate chassis with independent control and data planes for devices attached to non-VLT ports.
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Virtual Link Trunking (VLT)