WireGuard MTU Calculator
WireGuard adds about 60 bytes to every packet, so over a normal 1500-byte link the inner MTU is 1440.
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Encapsulation in the Path
Inner MTU
1500 − 60 bytes of headers
TCP MSS (IPv4)
TCP MSS (IPv6)
Largest Ping (IPv4)
Clamp MSS (nftables)
nft add rule inet filter forward tcp flags syn tcp option maxseg size set 1400
MTU & MSS Calculator
WireGuard on a 1500-byte link
Overhead60 bytes
Inner MTU1440
TCP MSS (IPv4)1400
TCP MSS (IPv6)1380
Over PPPoE (1492)1432
Testping -M do -s 1412 <host>
If the inner interface keeps an MTU of 1500, packets larger than 1440 bytes are fragmented or dropped. The usual symptom: ping and small requests work, large downloads and TLS handshakes hang.
Set the WireGuard interface's MTU to 1440, or clamp TCP MSS to 1400 on the router.
MTU by Tunnel
Questions
What MTU should I use for WireGuard?
1440 over a standard 1500-byte link; 1432 over PPPoE.
How much overhead does WireGuard add?
About 60 bytes per packet.
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