MTU Setting

Defguard client supports manual MTU configuration to ensure stable VPN connections on mobile and carrier-grade networks. These networks often enforce lower MTU limits, which can cause VPN traffic to be dropped even though the tunnel appears connected.

Adjusting the MTU reduces packet size so traffic fits within network constraints, improving reliability without server-side changes. Typical working values are in the 1300-1500 range.

How to find MTU setting?

1. If you don't have Defguard in full view mode, open Defguard from tray view, and click Open Defguard

1. Go to settings tab.

1. Find MTU setting

When to adjust the MTU

Consider lowering the MTU when the tunnel connects successfully but you experience symptoms such as:

• Connections that hang or time out even though the client shows as connected.

• Web pages that start loading and then stall, or large downloads that stall.

• Traffic working over some networks (for example, home Wi-Fi) but not others (for example, mobile hotspots or hotel Wi-Fi).

These are classic signs of packets being too large for the underlying network path.

How to choose a value

If the default value doesn't work, try progressively lower values within the 1300-1500 range until the connection is stable. A common safe value for problematic networks is 1280. Lowering the MTU too far reduces throughput, so use the highest value that keeps the connection reliable.

If lowering the MTU does not resolve your issue, see the troubleshooting guide Client connects but cannot reach VPN servers (MTU).

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