Service Manual

Figure 119. Enhanced VLT
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.
• 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).
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
trac on a chassis does not traverse the VLTi and takes the shortest path to the destination via directly attached links.
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 Congure Rapid Spanning Tree.
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Virtual Link Trunking (VLT)