How to setup tagged VLANs on Mac OS X

1. From the Apple menu (upper left corner of your desktop) choose System Preferences…
2. Open Network
3. In the toolbar below all of your network interfaces, click the gear wheel to access a dropdown menu
4. From that dropdown menu, select Manage Virtual Interfaces…
5. Click on + to access another dropdown menu
6. From that dropdown menu, select New VLAN…
7. Enter an appropriate name for your new VLAN, e.g. DMZ
8. Enter the desired tag, e.g. 23
9. Choose the correct physical interface, normally Ethernet
10. Click Create
11. Click Done
12. Configure your new VLAN interface as you would configure a physical interface, e.g. assign it an IP address, network mask, etc.
13. Click Apply
14. Close the network preferences window.

Weitere Informationen: http://www.ogris.de/howtos/macosx-tagged-vlans.html