Users Guide

• Uplinks — An edge port link on the first two aggregation switches in the VLT fabric that connects to
outside the fabric.
• Downlinks — An edge port link that connects the access switches to the access layer. For example,
servers or ToR elements.
• Fabric Interlinks (Fabric Links) — The fabric interlink bandwidth is fixed: 10 Gb or 40 Gb.
– For a one-tier fabric, fabric interlinks connect a pair of aggregation switches.
– For a two-tier fabric, fabric interlinks connect the aggregation switches to the access switches.
– For a three-tier fabric, fabric interlinks connect the core, aggregation, and access switches
together.
VLT Components
VLT peer switches have independent management planes. A VLT interconnect (VLTi) between the VLT
chassis maintains synchronization of Layer 2 and Layer 3 control planes across the two VLT peer
switches. The VLTi uses either 10 Gb or 40 Gb 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
incorrectly identified as VLTi failures by the software. VLT ensures that local traffic on a chassis does not
traverse the VLTi and takes the shortest path to the destination using direct links.
Figure 7. VLT Components
Typical VLT Topology
The VLT domain uses VLTi links between VLT peers and VLT port-channels to connect to a single access
switch, a switch stack, a server supporting LACP on its NIC, or another VLT domain. The backup-link
connects through the OOB management network. Some hosts can connect through the non-VLT ports.
Supported Fabric Types
29