本机16688端口不开放，如何转发到已经开放的端口上，如下：

1、查看端口使用的情况

[root@tstest ~]# netstat -ntal

Active Internet connections (servers and established)

Proto Recv-Q Send-Q Local Address               Foreign Address             State

tcp        0      0 127.0.0.1:9000              0.0.0.0:*                   LISTEN

tcp        0      0 0.0.0.0:3306                0.0.0.0:*                   LISTEN

tcp        0      0 0.0.0.0:80                  0.0.0.0:*                   LISTEN

tcp        0      0 192.168.2.177:53            0.0.0.0:*                   LISTEN

tcp        0      0 192.168.2.35:53             0.0.0.0:*                   LISTEN

tcp        0      0 127.0.0.1:53                0.0.0.0:*                   LISTEN

tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN

tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN

tcp        0      0 127.0.0.1:953               0.0.0.0:*                   LISTEN

tcp        0      0 192.168.2.35:22             192.168.2.165:49574         ESTABLISHED

tcp        0      0 :::8080                     :::*                        LISTEN

tcp        0      0 :::22                       :::*                        LISTEN

tcp        0      0 ::1:25                      :::*                        LISTEN

tcp        0      0 ::1:953                     :::*                        LISTEN

2、启用gate转发

编辑/etc/sysctl.conf，设置

net.ipv4.ip_forward = 1

执行：

# sysctl -p

3、例：添加*nat规则，连接服务器的1668端口，转发到22端口上

*nat

:PREROUTING ACCEPT [0:0]

:POSTROUTING ACCEPT [0:0]

:OUTPUT ACCEPT [0:0]

-A PREROUTING -p tcp -i eth0 -d 192.168.2.35 --dport 16688 -j DNAT --to 192.168.2.35:22

COMMIT

4、telnet 测试

5、以上只是使用了在外面的情况，但如果在服务器里边是使用不到43999端口的。

[root@tstest ~]# ssh 192.168.2.35 -p 16688

ssh: connect to host 192.168.2.35 port 16688: Connection refused

6、这里我们还可以在里边进行设置本地转发。

iptables -t -A OUTPUT -p tcp -d 192.168.2.35 --dport 16688 -j DNAT --to 127.0.0.1:22

7、再从本地进行测试，也是可以连接了，虽然端口是没有开启的。

ssh 192.168.2.35 -p 16688

The authenticity of host '[192.168.2.35]:16688 ([192.168.2.35]:16688)' can't be established.

RSA key fingerprint is 13:02:d6:d5:49:e7:05:ce:48:c8:56:d9:b8:b2:06:38.

Are you sure you want to continue connecting (yes/no)?