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•
VLT domain — This domain includes both the VLT peer devices, VLT interconnect, and all of the port
channels in the VLT connected to the attached devices. It is also associated to the configuration mode
that you must use to assign VLT global parameters.
•
VLT peer device — One of a pair of devices that are connected with the special port channel known as
the VLT interconnect (VLTi).
VLT peer switches have independent management planes. A VLT interconnect between the VLT chassis
maintains synchronization of L2/L3 control planes across the two VLT peer switches.
A separate backup link maintains heartbeat messages across an out-of-band (OOB) management network.
The backup link ensures that node failure conditions are correctly detected and are not confused with failures
of the VLT interconnect. VLT ensures that local traffic on a chassis does not traverse the VLTi and takes the
shortest path to the destination via directly attached links.
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. Refer to
•
VLT port channel interfaces must be switch ports.
•
If you include RSTP on the system, configure it before VLT. Refer to
•
If you include PVST on the system, configure it before VLT. Refer to
•
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
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.
•
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.
VLT and
Stacking.
Configure Rapid Spanning
PVST
Configuration.
RSTP and VLT
Virtual Link Trunking (VLT)
Tree.
for
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Table of Contents
Troubleshooting
