PPPoE MTU Calculator
PPPoE adds about 8 bytes to every packet, so over a normal 1500-byte link the inner MTU is 1492.
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Encapsulation in the Path
Inner MTU
1500 − 8 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 1452
MTU & MSS Calculator
PPPoE on a 1500-byte link
Overhead8 bytes
Inner MTU1492
TCP MSS (IPv4)1452
TCP MSS (IPv6)1432
Over PPPoE (1492)1484
Testping -M do -s 1464 <host>
If the inner interface keeps an MTU of 1500, packets larger than 1492 bytes are fragmented or dropped. The usual symptom: ping and small requests work, large downloads and TLS handshakes hang.
Set the PPPoE interface's MTU to 1492, or clamp TCP MSS to 1452 on the router.
MTU by Tunnel
Questions
What MTU should I use for PPPoE?
1492 over a standard 1500-byte link; 1484 over PPPoE.
How much overhead does PPPoE add?
About 8 bytes per packet.
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