MAC addresses in a VSS cluster

As you might know, creating a VSS on Cisco Catalyst 4500-X switches is pretty easy and there are many many guides with information how to do this. I think THIS guide is one of the best to do this.

However, there is one additional note which is not mentioned on that (and other) blogs if you are planning to use multiple Catalyst 4500-X VSS clusters. This is related to the switch MAC address.

By default, all MAC addresses used by the Catalyst 4500-X VSS cluster is automatically generated and is based on the VSS domain ID. But what does this mean?

If you’re planning to use multiple VSS clusters in the same network and in the same VLAN(s), you’ll end up with duplicate MAC addresses. I’m sure I don’t have to tell you that this is something you don’t want: it brakes a lot of things in your network.