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VLT Terminology
The following are key VLT terms.
•
Virtual link trunk (VLT) — The combined port channel between an attached device and the VLT peer
switches.
•
VLT backup link — The backup link monitors the vitality of VLT peer switches. The backup link sends
configurable, periodic keep alive messages between the VLT peer switches.
•
VLT interconnect (VLTi) — The link used to synchronize states between the VLT peer switches. Both
ends must be on 10G or 40G interfaces.
•
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. The VLT interconnect
uses either 10G or 40G user ports on the chassis.
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.
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
•
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
•
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.
for guidelines to avoid traffic loss.
Configure Rapid Spanning
Virtual Link Trunking (VLT)
Tree.
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Table of Contents
Troubleshooting
