Q I laid away one of the last old-design Mac Pros, and have just hooked it up to my network, with a BT modem-router and AirPort Extreme base station.

However every time I start the Mac Pro up it cancels out my Internet connection. The Mac has been checked by the supplier, who insists that it is working fine. Is my modem-router too old for this new computer?

A No. However you will need to check your network configuration carefully before it will work. Chances are that you are running two DHCP servers, which will cause chaos.

Open the configuration screens for your modem-router and turn its DHCP server off, leaving the AirPort base station to hand out IP addresses.

Open the Network pane on your Mac Pro, and set it to use a fixed IP address on the same sub-net as the modem-router. For example, if the modem-router has an IP address of 192.168.1.1, set the Mac Pro to use a fixed IP address of 192.168.1.10, perhaps. Set the Subnet mask to 255.255.255.0, with DNS Servers as the modem-router’s IP address first, followed by the two DNS servers for your ISP.

Comments You will also need to restrict the range of IP addresses which the base station uses, so that they do not clash with the fixed addresses of your modem-router or Mac Pro.

General network troubleshooting is detailed here, and simple network setup here.

Updated from the original, which was first published in MacUser volume 30 issue 02, 2014.