Switch High Availability and the Control Plane

There are various Switch high availability options that can be used to provide redundancy and resiliency to a network. The way these solutions deal with the control plane is an important part of deciding which to use.

VSS and StackWise (including StackWise Virtual) are designed to merge multiple physical switches into one logical unit, but they operate with a single control plane. This means there is only one physical switch that is actively using its control plane, managing the entire stack or VSS system. This provides equipment-level redundancy. If the control plane fails, the whole stack or VSS system is affected. However, this does not mean that the whole logical switch has failed. The other switch or switches will take over control plane operations almost immediately, with little to no downtime.

vPC can also make multiple switches appear as a single logical unit, but with a crucial difference: each switch retains its own control plane. This independent control plane setup provides system-level redundancy because they both operate at the same time. This adds an additional aspect of redundancy.

However, vPC can incorporate no more than two switches in a single vPC arrangement. Also, vPC is only available on Cisco Nexus switches, which are designed for data centers and other high-availability applications. This is why vPC offers a higher level of redundancy compared to VSS or StackWise.

Links

https://networklessons.com/switching/cisco-switch-virtualization