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MTU settings for slow or fragmented connections

3 min read·Updated April 5, 2026

Adjusting MTU can fix slow speeds and packet fragmentation through the VPN tunnel.

MTU (Maximum Transmission Unit) defines the largest packet size that can be sent through a network. VPN encryption overhead can cause packets to exceed the network's MTU, causing fragmentation and slowdowns.

# Windows — find optimal MTU (Command Prompt, run as admin)
ping -f -l 1400 8.8.8.8
# Decrease size until you stop seeing "Packet needs to be fragmented"
# Optimal MTU = last working size + 28
  1. 1Go to Settings → Advanced → MTU
  2. 2Change from "Auto" to "Manual"
  3. 3Enter the value you calculated (typically 1280–1420)
  4. 4Click Save and reconnect

Start with 1300 if unsure — this works for most connections. WireGuard typically needs MTU of 1420 or lower.

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