Find Maximum Transfer Unit(MTU) of a network using MTU Path Commandline tool

MTU Path command line tool is used to find the path MTU size of a network.

Features:

  • Supports IPv4 and IPv6 networks.
  • Leverages multiple measurement strategies to account for a variety of network conditions.
  • Find IPv4 path MTU thru misconfigured PMTU black hole routers.
  • Warning messages alert of inconsistent results or exceptional conditions potentially affecting the path size estimate.
  • Partial path estimate is possible if the destination host offline.
  • Windows XP, Vista, 7/8/10 platforms

More details about the MTU Path tool: MTU Path

This tool is useful in finding the optimal MTU or a network path. The size of MTU is in bytes.

The MTU value found by this tool is the maximum value MTU that could pass through the network without being defragmented.

Mtupath Tool Usage

-4 : This is used to find the MTU of IPv4 packets

-6 : This is used to find the MTU of IPv6 packets

Download and install the MTU path tool

  1. First download the MTU path tool from the website: https://www.iea-software.com/products/mtupath/
  2. Copy the mtupath.exe to the Windows OS folder “C:\Windows\System32“

Run Command Prompt(CMD) or PowerShell

Command prompt or Powershell can be used to run the command line tool mturoute.exe.

To run the Command prompt in Administrator mode do the following:

  • Click on the Start menu and type “cmd”.
  • Right-click on Command prompt app and select “Run as administrator“.

To run the Powershell in Administrator mode do the following:

  • Open Windows Start Menu > Windows Powershell.
  • Right-click the Windows Powershell and select “Run as Administrator“.

Check the MTU of the Network Interface Card

Before using MTUpath tool make sure the MTU for the Network Interface Card is 1500.

  • Open Command Prompt or Powershell.
  • To show the MTU of IPv4 packets for each network adapter use the command: netsh interface ipv4 show subinterface
  • To show the MTU of IPv6 packets for each network adapter use the command: netsh interface ipv6 show subinterface

Make sure the MTU for the Network adapter which is used to connect to the internet is 1500.

Find optimal MTU of the Internet using the mtupath tool

Things to note before using the mtupath tool:

  1. The Network Interface card(NIC) is used to connect to the internet. It could be Ethernet NIC or a wireless NIC. The Network Interface card(NIC) must be a physical card and not a virtual one.
  2. The website/IPv4/IPv6 address of the remote host on the internet. It’s better that you choose a website/IPv4/IPv6 address that is located farthest from your location. When a website hosted on another continent is used the route includes multiple routers which are helpful in finding the optimal path MTU.
  3. Internet Service Provider(ISP): You may have subscribed to multiple ISPs for an Internet connection. Each of the ISP networks may have a different MTU. In this case, if the Network Interface card(NIC) connects to the internet using various ISP’s services will you must find out MTU for each of the ISPs. You will have to set the MTU for the Network Interface card(NIC) which is the lowest among multiple ISPs.

Example_1

My computer connects to the internet using two ISP. My Wireless network Interface Card is used to connect to both of the ISPs. So I Need to find the MTU of IPv4 packets for both ISPs. Then I will use the lowest MTU.

To find the MTU of Ipv4 packets for ISP_1, use the following command:

  • Connect to the Internet using ISP_1.
  • Start Command Prompt or Powershell.
  • Run the command: mtupath -4 http://www.bing.com

Run the command: mtupath -4 8.8.8.8.

Path MTU of ISP_1: 1480 bytes

To find the MTU of Ipv4 packets for ISP_2, use the following command:

  • Connect to the Internet using ISP_2.
  • Start Command Prompt or Powershell.
  • Run the command: mtupath -4 http://www.bing.com

Run the command: mtupath -4 8.8.8.8

Path MTU of ISP_2: 1400 bytes

The optimal size of MTU for IPv4 packets that should be used for my Network Interface Card is 1400 bytes.

Example_2

My computer connects to the internet using two ISP which are capable of IPv6 traffic. My Wireless network Interface Card is used to connect to both of the ISPs. I Need to find the MTU of IPv6 packets for both ISPs. Then I will use the lowest MTU out of both.

To find the MTU of Ipv6 packets for ISP_1, use the following command:

  • Connect to the Internet using ISP_1.
  • Start Command Prompt or Powershell.
  • Run the command: mtupath -6 http://www.google.com
  • Run the command: mtupath -6 2001:4860:4860:0:0:0:0:8888

Path MTU of ISP_1: 1400 bytes

To find the MTU of Ipv6 packets for ISP_2, use the following command:

  • Connect to the Internet using ISP_2.
  • Start Command Prompt or Powershell.
  • Run the command: mtupath -6 http://www.google.com

Run the command: mtupath -6 2001:4860:4860:0:0:0:0:8888

Path MTU of ISP_2: 1400 bytes

The optimal size of MTU for IPv6 packets that should be used for my Network Interface Card is 1400 bytes.