How to Check and Change MTU Size in Windows 11 Using netsh

The Maximum Transmission Unit (MTU) specifies the largest data packet, measured in bytes, that a network interface can transmit without fragmenting the packet into smaller frames. When your local Windows 11 MTU value does not match the optimal packet handling capabilities of your internet service provider or VPN tunnel, network packets become fragmented or dropped. This results in sluggish page loading, latency spikes in online gaming, and reduced throughput. Using the Windows command-line utility netsh, you can query current network interfaces and customise your MTU size for optimal stability.

Understanding Default MTU Values and Fragmentation

Standard Ethernet connections operate with a default MTU of 1500 bytes. However, certain network encapsulations and internet connection types require lower thresholds to accommodate protocol headers:

• Standard Ethernet: 1500 bytes
• PPPoE Connections (common for DSL and some fibre ISPs): 1492 bytes
• VPN Tunnels (WireGuard, OpenVPN, IPsec): Typically 1380 to 1420 bytes to allow for encryption overhead

When packets exceed the maximum MTU of any intermediary router, routers must break packets apart, creating computational overhead and packet retransmissions.

How to Check Current MTU Values in Windows 11

You can view the active MTU assigned to every physical and virtual network adapter using PowerShell or Command Prompt:

1. Right-click the Start button and select Terminal (Admin).
2. Ensure you are in an elevated prompt (PowerShell or Command Prompt).
3. Enter the following command and press Enter:

   netsh interface ipv4 show subinterfaces

4. Review the output table. The command displays three columns: MTU, MediaState, and Interface. Note the exact name of your active adapter (such as Wi-Fi or Ethernet) and its current MTU value.

How to Test for the Optimal MTU Without Packet Fragmentation

Before modifying settings, identify the exact threshold where your packets fragment by executing an ICMP ping test with the “Don’t Fragment” flag enabled:

1. In your elevated terminal, run:

   ping 1.1.1.1 -f -l 1472

2. If you receive the error Packet needs to be fragmented but DF set, lower the packet size by 10 or 12 bytes (for example, 1460, 1452, 1440) until you receive successful ping replies without packet loss.
3. Once you locate the highest working size that does not fragment, add 28 bytes (20 bytes for the IP header and 8 bytes for the ICMP header) to calculate your true optimal MTU. For example, if 1464 bytes succeeds, 1464 + 28 = 1492 MTU.

How to Change MTU Size in Windows 11 Using netsh

Once you know the interface name and targeted MTU value, apply the configuration permanently using netsh:

1. In the elevated terminal window, type the following command, replacing "Wi-Fi" with your exact interface name and 1492 with your calculated MTU:

   netsh interface ipv4 set subinterface "Wi-Fi" mtu=1492 store=persistent

2. Press Enter. You should receive a confirmation message stating Ok.
3. If you also route IPv6 traffic over this interface, apply the matching configuration to the IPv6 stack:

   netsh interface ipv6 set subinterface "Wi-Fi" mtu=1492 store=persistent

4. Verify the change immediately by re-running:

   netsh interface ipv4 show subinterfaces

How to Restore Default MTU Settings in Windows 11

If you experience unexpected connection issues or change internet service providers, restore your interface to standard Ethernet specifications:

1. Open an elevated terminal prompt.
2. Execute:

   netsh interface ipv4 set subinterface "Wi-Fi" mtu=1500 store=persistent

3. Confirm that the adapter reflects 1500 bytes to resume standard operation.