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.

There are a few options to get rid of these duplicate MAC addresses. The most easy (and my personal recommend this for most cases) is simply by using a different VSS domain ID for every VSS cluster. The MAC addresses can still be automatically generated as it is by default, and you will not end up with duplicate MACs.

There are two additional options:

  • Use the system MAC address
  • Use a manual configured MAC address

Configuration is done inside the “switch virtual domain” configuration. This table shows all the options, where “use-virtual” is configured by default.

Switch(config)# switch virtual domain domain_id 

Switch(config-vs-domain)# mac-address use-virtual 

Switch(config-vs-domain)# mac-address mac-address 

Switch(config-vs-domain)# mac-address chassis