D-Link Router User Manual page 145

Section 5 - Troubleshooting
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 actual MTU size 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 router with the proper MTU size.
To change the MTU rate on your router follow the steps below:
• Navigate to the Internet configuration page (see Internet on page 9 for details).
• To change the MTU, enter the number in the MTU field and click Apply to save your settings.
• Test your email. If changing the MTU does not resolve the problem, continue changing the MTU in increments
of ten.
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