outside the VLT domain.) VLT provides Layer 2 multipathing, creating redundancy through increased bandwidth,
enabling multiple parallel paths between nodes and load-balancing traffic where alternative paths exist.
For information about VLT, see the FTOS Configuration Guide for either the S4810 or the Z9000 at https://
www.force10networks.com/CSPortal20/KnowledgeBase/Documentation.aspx. For more information about VLT, see
Selecting a VLT Fabric Design
.
Virtual link trunking offers the following benefits:
•
Allows a single device to use a LAG across two upstream devices
•
Eliminates Spanning Tree protocol (STP) - blocked ports
•
Provides a loop-free topology
•
Uses all available uplink bandwidth
•
Provides fast convergence if either the link or a device fails
•
Optimized forwarding with Virtual Router Redundancy Protocol (VRRP)
•
Provides link-level resiliency
•
Assures high availability
CAUTION:
Dell Networking recommends not enabling Stacking and VLT simultaneously.
If both are enabled at the same time, unexpected behavior occurs.
Multi-domain VLT
An multi-domain VLT (mVLT) configuration allows two different VLT domains connected by a standard Link Aggregation
Control protocol (LACP) LAG to form a loop-free Layer 2 topology in the aggregation layer. This configuration supports a
maximum of 4 units, increasing the number of available ports and allowing for dual redundancy of the VLT. For more
information about mVLT deployments, see
Selecting a Layer 2 VLT Fabric Design
.
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 health of VLT peer switches. The backup link sends
configurable, periodic keep alive messages between 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 VLT peer devices, the 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 must be used 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 Layer 2/ Layer 3 control planes across the two VLT peer switches. The VLT interconnect uses either
10G or 40G user ports on the switch.
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
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