帮服务器上某个端口转发到远端另一个端口
iptables -t nat -A PREROUTING -p tcp --dport 7890 -j DNAT --to-destination 192.168.1.100:7890任何访问服务器的 7890端口的请求都会转发到 192.168.1.100:7890
iptables -t nat -A PREROUTING -p tcp --dport 7890 -j DNAT --to-destination 192.168.1.100:7890