Note the use tcpdump

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1, if you use tcpdump to view seq and ack when this command is best used with the -S

sudo tcpdump -S -i ens33 -v host proxy.tencent.com

And when no added -S -S, ack different three-way handshake
without -S below, returned when the third handshake ack is always 1 (this is a relative value)

after the addition of third handshake is displayed ack normal

Reference article
https://blog.csdn.net/qq_32503701/article/details/53559759#commentBox