Testing for MTU on a Good Line (4)

18. Press the "Test MTU" button and if you get ping responses all is well and you can try another of your frequently visited sites. If you get the "Don't Fragment Bit Set" warning message the site uses a smaller MTU than your ISP which means you will have to try smaller MTU's in the "MTU value to test box". (Remember, if you don't get a response it may be that the server is set to not respond to pings - www.microsoft.com is one such site)
    
19. Continue testing sites/values until you know the largest MTU you can use to reach the sites you visit frequently.
    
20. Set the MTU you have decided on using the procedure detailed earlier then reboot your computer.
    

I am indebted to Malcolm Reeves for detailing a procedure on his website for testing MTUs. The procedure outlined on the previous few pages is developed from Malcolm's procedure and I like to acknowledge the source of my information.