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Explanation: MTU

This setting toggles on or off manual configuration of the MTU value. If disabled, it allows you to enter a custom value.

Maximum transmission unit (MTU) defines the largest data packet that can be transmitted over your internet connection. In essence, it can be compared to the height limit of tunnels for cars and trucks. Just like a car or a truck can't fit through the tunnel if they exceed the height limit, a packet that is larger than the MTU cannot pass through the network.

When you download anything from the Internet, such as a website, the content breaks down into several smaller "chunks" and are then sent over the network to your device. Once downloaded, your computer will reassemble these packets and you can then view the content.

A data packet contains two main parts: the header and the payload. Much like when you send a package in the mail, the header contains information about the packet's source and destination address, while the payload holds the actual packet's content.

Packets sent over the internet travel across multiple networks, switches, routers, and servers. If the packet size is too large at any of these points, the packet becomes fragmented (split into smaller chunks). If fragmenting a packet isn't possible, it will instead be discarded.

If packets become fragmented, you may notice that websites take longer to load, or aren't loaded at all.

When your traffic becomes encrypted by a VPN, the VPN adds an additional header to the package and encrypts the original packet. The MTU setting in the client control the size of the VPN packet to ensure that the total size of the VPN packet does not exceed the set value. In most cases, the default value works great. However, some networks (such as PPPoE) may need a lower value of MTU.

The default MTU value of OpenVPN is 1500 and for WireGuard it is 1420. If you have issues with certain websites or your VPN connection occasionally drops, try changing the MTU value. The MTU value you need to set differs depending on OpenVPN or WireGuard. Some common MTU values you can try for WireGuard are 1412, 1400, and 1372.