calc.engineer / Homelab & Networking / Wireguard MTU

Wireguard MTU v1.0.0

Calculate the optimal MTU for a WireGuard VPN tunnel interface with a detailed overhead breakdown. Accounts for WireGuard header (32 bytes), outer IP header (20 bytes IPv4 or 40 bytes IPv6), UDP header (8 bytes), and optional PPPoE encapsulation (8 bytes). Prevents fragmentation and PMTUD black holes by computing the maximum inner packet size that fits within the physical link MTU. Essential for WireGuard setup on residential ISP connections (PPPoE), IPv6 tunnels, and any VPN where incorrect MTU causes slow or stalled connections.

← from tcp_throughput
MTU of the underlying physical or virtual network interface in bytes
Fill in the inputs and Compute to see the structured result.

From an agent (MCP) or the API

curl -X POST https://calc.engineer/api/wireguard_mtu \
  -H "Content-Type: application/json" \
  -d '{"interface_mtu": …, "ipv6": …, "over_pppoe": …}'

MCP: connect to https://calc.engineer/mcp and call wireguard_mtu.

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