[lwip-devel] [bug #36234] LISTEN send RST for incoming ACKs with seqno == ackno + 1

[Esa Hill]

Follow-up Comment #8, bug #36234 (project lwip):

I attached wireshark log and dug little deeper for the reason why we did this
change.

In the log, packet 13 is marked by wireshark as 'TCP ACKed unseen segment'
After that it takes about 17 seconds before Modbus connection is reopened.
This long period might be PC's fault, but if seqno is correct, SYN is sent
right away.

I'm quoting same chapter from RCF as the original bug creator, RFC 793 page
35, state CLOSED:

"1.  If the connection does not exist (CLOSED) then a reset is sent..."

"If the incoming segment has an ACK field, the reset takes its
    sequence number from the ACK field of the segment"

The packet 13 (RST ACK) has seqno=45, when the incoming packet 10 has
ackno=44.

If I have understood RFC correctly, RST ACK should use the ackno from the
received packet. Now it seems to use FIN ACK + 1 (which never left the
device).

I can create new bug for our case if you want, but for me these look like same
case. In both states it should use ackno from last segment.

(file #31421)
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Additional Item Attachment:

File name: seqno_plus_1.pcap              Size:1 KB


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