[Bug 250363] [tcp] data in syn_ack should be ignored

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Wed Feb 17 13:20:57 UTC 2021


--- Comment #2 from Michael Tuexen <tuexen at freebsd.org> ---
(In reply to Richard Scheffenegger from comment #1)
This report is not about TFO... Are you sure it is not allowed? My reading of
RFC 793 is as follows. We are in SYN-SENT. So we are on page 66. The next text
on page 68, which applies is:

If SND.UNA > ISS (our SYN has been ACKed), change the connection
state to ESTABLISHED, form an ACK segment


and send it.  Data or controls which were queued for
transmission may be included.  If there are other controls or
text in the segment then continue processing at the sixth step
below where the URG bit is checked, otherwise return.

Then is step 7, we would process the text and send


So my reading is that the response according to RFC 793 should be
* send an ACK for the SYN in the SYN-ACK, move to established
* send an ACK for the received data.

Is my understanding wrong?

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