从zom3y3大佬ppt上看到后，直觉告诉可以基于这玩意好好研究...

安装conntrack

#Ubuntu/Debian
sudo apt-get install conntrack
#CentOS
sudo yum install conntrack-tools libnetfilter_conntrack
#execute
sudo conntrack -L

修改代码

dport = int(os.popen("sudo conntrack -L |grep \"src=%s\"  | grep tcp | grep \"sport=%d\"| tail -n 1" % (ip, port,)).read().split("dport=", 1)[1].split(" ", 1)[0])