How to Establish the Allowable MTU Size When You Are Using Internet Connection Sharing on PPPoE (Q314100)

IMPORTANT : This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the “Restoring the Registry” Help topic in Regedit.exe or the “Restoring a Registry Key” Help topic in Regedt32.exe.

This article describes how to establish the maximum transmission unit (MTU) size for using Internet Connection Sharing (ICS) if your outbound connection uses Point-to-Point Protocol over Ethernet (PPPoE). If the setting for MTU size is too high, clients that are using the ICS connection may not be able to browse some Web sites or send messages that contain attachments.

PPPoE is a method for establishing Point-to-Point Protocol (PPP) connections through Ethernet network adapters. PPPoE requires that, on all client computers, you lower the setting for maximum transmission unit (MTU) size to a value no higher than 1,492. (The default is 1,500.) In some cases, a value lower than 1,492 may be necessary.

Click here for the kb article from Microsoft.