Alter the MTU on Mac OS X 10.3 (Panther)
Aim of this article:
This document provides a guide to altering the MTU settings of an Ethernet card on Apple Mac OS X 10.3 (Panther). It may be necessary to alter the MTU if you are having problems with speed or access to some Web sites.
Altering the MTU:
Begin by clicking 
-> System Preferences.
Double click Network.
Select the drop down options for Show and then click Built-in Ethernet.
Select Ethernet.
Select the menu for Configure and click Manually(Advanced).
Beneath the Maximum Packet Size (MTU) heading select Custom and then enter a MTU value. The following settings are often used to resolve problems:
