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MTU troubleshooting article from Cisco for a brief overview of the problem.
DrTCP can be used to lower the MTU on almost any server available and a step by step guide is shown below.
Download DrTCP and open the application. Select the proper network adapter from the pull down menu and change the MTU to 1400 bytes. Important Note: There may be more than one network adapter showing in the pull down menu. You must make sure you change the MTU on the correct network adapter associated with your secure server. If there is any doubt as to which adapter is the correct one, change the MTU on all adapters. Restart the Server. The changes will not be set unless your completely restarted your Server.
Picture by Andy Houtz
After the PC has restarted, open a HTTPS session and test your connectivity to the server as well as any applications.
Repeat Steps 1 and 2 but increase your MTU to 1420 bytes. Continue to repeat Steps 1 and 2 (increasing your MTU by 20 bytes each time) until your session does not function correctly and back the MTU down to the last known fully functional MTU size. Remember you must restart the PC/Server after every MTU change.
If your HTTPS session does not work correctly at 1400 bytes
Repeat Steps 1 and 2 but decrease your MTU to 1380 bytes. Continue to repeat Steps 1 and 2 (decreasing your MTU by 20 bytes each time) until your session functions correctly. Remember you must restart the PC/Server after every MTU change.
If you have a network with more than one server, all NICs, adapters, and router(s) should have the same MTU setting.
Andy Houtz DSL