[lwip-users] ACK missing after SYN, strange high Ack Num

[Jochen Strohbeck]

Hello,
I'm running a Python requests script which aborts after running ca. 30
minutes with timeout > 5s.

Telling from Wireshark, usually SYN is followed by SYN,ACK:

192.168.0.7         192.168.0.100    TCP        66           [TCP Port
numbers reused] 57847 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 WS=256
SACK_PERM=1
192.168.0.100    192.168.0.7         TCP        60           80 → 57847
[SYN, ACK] Seq=0 Ack=1 Win=2920 Len=0 MSS=1460
192.168.0.7         192.168.0.100    TCP        54           57847 → 80
[ACK] Seq=1 Ack=1 Win=64240 Len=0


If the timeout occurs, I see SYN is followed by ACK. First thought was
that the ACK is lost but then I noticed this strange very high Ack
Number which seems to result in a RST:

192.168.0.7         192.168.0.100    TCP        66           [TCP Port
numbers reused] 57848 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 WS=256
SACK_PERM=1
192.168.0.100    192.168.0.7         TCP        60           80 → 57848
[ACK] Seq=1 Ack=4294953032 Win=2762 Len=0
192.168.0.7         192.168.0.100    TCP        54           57848 → 80
[RST] Seq=4294953032 Win=0 Len=0

Any idea about the root cause and how to get rid of this?
Thanks!