Deployment Guide

Figure 123. Multi-Domain VLT Example
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 congurable, 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 conguration 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).
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
• VLT port channel interfaces must be switch ports.
• If you include RSTP on the system, congure it before VLT. Refer to RSTP Conguration.
• 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.
Virtual Link Trunking (VLT)
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