google path mtu?

Matthew Luckie mjl at
Tue Jan 20 17:14:30 CET 2015

> No, the minimum MTU is a requirement on links, not hosts. Hosts are
> always allowed to send smaller packets than the MTU if they want
> to. Also, the MSS includes TCP options, so it might be 1208 on a
> 1280-byte link.

There are conflicting RFCs, but the consensus seems to be the MSS is
computed using the minimum size IP and TCP headers (without options).
If a host sends packets with options, it is expected to count those
against the packet size it sends.
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