Windows 10 and 11 AlwaysOn VPN - Adjusting MTU for HACC AlwaysOn VPN

This procedure is for adjusting the MTU (Maximum Transmission Unit) on a user’s PC when connected to the HACC AlwaysOn VPN, to ensure better connectivity, especially with T-Mobile’s service.

Prerequisites:

  • Remote administrative access to the user's PC.
  • Access to Windows Shell or PowerShell Command line.
  • HACC AlwaysOn VPN installed and connected.

Procedure:

  1. Launch Command Prompt (CMD):

    • Right-click on CMD and select Run as Administrator.

  2. Check the current MTU setting for HACC AlwaysOn VPN:

    • Type the following command and press Enter:
       
      netsh interface ipv4 show subinterfaces
       
    • The MTU for the HACC AlwaysOn VPN should be displayed. If not, launch the VPN and try again.

  3. Change the MTU size:

    • Type the following command to set the MTU size to 1350:
       
      netsh interface ipv4 set subinterface “HACC AlwaysOn VPN” mtu=1350 store=persistent
       
    • This adjusts the MTU size, as T-Mobile’s service is optimized for this setting when using HACC’s VPN.

  4. Verify the change:

    • Type the following command again to verify the MTU value:
       
      netsh interface ipv4 show subinterfaces
       
    • The output should show the MTU value set to 1350.

  5. Reboot the PC:

    • Restart the user’s PC to apply the changes. After reboot, you can check again using the netsh command to confirm the MTU setting persists.

  6. Exit Remote Session:

    • If the connection seems stable, you can exit the remote session.
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