802.1Q VLAN MTU Calculator
802.1Q VLAN adds about 4 bytes to every packet, so over a normal 1500-byte link the inner MTU is 1496.
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Encapsulation in the Path
Inner MTU
1500 − 4 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 1456
MTU & MSS Calculator
802.1Q VLAN on a 1500-byte link
Overhead4 bytes
Inner MTU1496
TCP MSS (IPv4)1456
TCP MSS (IPv6)1436
Over PPPoE (1492)1488
Testping -M do -s 1468 <host>
If the inner interface keeps an MTU of 1500, packets larger than 1496 bytes are fragmented or dropped. The usual symptom: ping and small requests work, large downloads and TLS handshakes hang.
Most switches and NICs carry the 4-byte VLAN tag without lowering the MTU, so this only matters on kit that does not.
Questions
What MTU should I use for 802.1Q VLAN?
1496 over a standard 1500-byte link; 1488 over PPPoE.
How much overhead does 802.1Q VLAN add?
About 4 bytes per packet.
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