To find the properSize, you’ll have to do a special ping of the destination you’re trying to go to. A destination could be another computer, or a URL.
Step 1 Click on Start and then click Run.
Step 2 Windows NT, 2000, and XP users type in cmd and press Enter (or click OK).
Step 3 Once the window opens, you’ll need to do a special ping. Use the following syntax:
ping [url] [-f] [-l] [value]
Example: ping yahoo.com -f -l 1472
You should start at 1472 and work your way down by 10 each time. Once you get a reply, go up by 2 until you get a fragmented packet. Take that value and add 28 to the value to account for the various TCP/IP headers. For example, lets say that 1452 was the proper value, the actualsize would be 1480, which is the optimum for the network we’re working with (1452+28=1480).
Once you find your MTU, you can now configure your with the proper MTU size.