What is MTU (Maximum Transmission Unit)?

In networking, maximum transmission unit (MTU) is a measurement representing the largest data packet that a network-connected device will accept.

MTU is measured in bytes — a “byte” is equal to 8 bits of information, meaning 8 ones and zeroes. 1,500 bytes is the maximum MTU size.

What is Jumbo Frame?

A jumbo frame is an Ethernet frame with a payload greater than the standard maximum transmission unit (MTU) of 1,500 bytes. Jumbo frames are used on local area networks that support at least 1 Gbps and can be as large as 9,000 bytes. It also depends on Vendor to Vendor.

What is the ideal MTU size?

Add 28 to that number (IP/ICMP headers) to get the optimal MTU setting. For example, if the largest packet size from ping tests is 1462, add 28 to 1462 to get a total of 1490 which is the optimal MTU setting.

How to check permitted MTU size?

You can check permitted MTU by doing ping sweep with Packet size value:

  1. In Windows, go to Start and select Run.
  2. Type in cmd Hit the enter key or click OK. The DOS prompt should open.
  3. At the DOS prompt, type in ping http://www.google.com -f -l 1492 and hit the Enter key:
  • The results above indicate that the packet needs to be fragmented. Repeat this test, lowering the size the packet in increments of +/-10 (e.g. 1472, 1462, 1440, 1400) until you have a packet size that does not fragment:

In this case fragment size set to 1270 Byte:

  1. Begin increasing the packet size from this number in small increments until you find the largest size that does not fragment. Add 28 to that number (IP/ICMP headers) to get the optimal MTU setting. For example, if the largest packet size from ping tests is 1462, add 28 to 1462 to get a total of 1490 which is the optimal MTU setting.
  2. Change the MTU on the routers WAN Setup.

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