A little while ago, our ISP decided to switch from a perfectly functioning direct TCP/IP connection to PPPoE. I asked them why they were doing this and received a less than coherent response which basically boiled down to "we can manage things easier". Fine for them, but of course it caused problems for their customers.

One of the problems is the MTU (Maximum Transmission Unit) setting commonly required for PPPoE (1492) which is not the default MTU setting for Mac OS (1500). When this setting is mismatched, one typically experiences problems which manifest themselves as timeouts on some web page loads and the retrieval of email.

The ISP's tech support didn't know anything about this, but after a small amount of digging I came up with the method for changing the MacOS MTU setting following a reboot. Without further ado, here is the procedure for others who run into this problem. This procedure applies specifically to the AirPort connection.

• Launch Terminal
• Browse to the following directory: /System/Library/SystemConfiguration/Kicker.bundle/Contents/Resources
• Use your favorite text editor to edit the file: enable-network
• Add this line before the 'exit' line: ifconfig en1 mtu 1492
• The AirPort card's MTU will now be set to 1492 when the system boots.