Take the following steps if you need to find out what MAC addresses are on the PBX:

1. Login to your PBX using your administrator account
2. Go to menu option 'System' and choose 'Diagnostics'
3. Click on 'Generate report' followed by 'Download'
4. Save the logfiles to your desktop and open it (using an unzip tool such as WinZIP)
5. Open the 'diag' file using your texteditor (such as wordpad/notepad) and scroll to 'Network Interfaces'

You will see all MAC addresses and other network related information in this section of the diag file.