SSH服务器实现telnet请求转发

本次实验做的工作如下图：

中间一台CentOS6通过SSH转发两边两台CentOS7的telnet通信。

• 首先，在右侧CentOS7上安装telnet服务

  [root@Shining ~]# yum install -y telnet telnet-server

• 启动telnet服务

  [root@Shining ~]# systemctl start telnet.socket 
  [root@Shining ~]# systemctl status telnet.socket 
  ● telnet.socket – Telnet Server Activation Socket 
  Loaded: loaded (/usr/lib/systemd/system/telnet.socket; disabled; vendor preset: disabled) 
  Active: active (listening) since Sun 2016-12-04 10:57:10 CST; 20min ago 
  Docs: man:telnetd(8) 
  Listen: [::]:23 (Stream) 
  Accepted: 2; Connected: 1

  Dec 04 10:57:10 Shining.ACG systemd[1]: Listening on Telnet Server Activation S…t. 
  Dec 04 10:57:10 Shining.ACG systemd[1]: Starting Telnet Server Activation Socket. 
  Dec 04 11:17:18 Shining.ACG systemd[1]: Listening on Telnet Server Activation S…t. 
  Hint: Some lines were ellipsized, use -l to show in full.

• 关闭防火墙：

  [root@Shining ~]# iptables -F

• 在左侧CentOS7上也安装telnet

  [root@Shining ~]# yum install -y telnet telnet-server

• 开启ssh转发：

  [root@Shining ~]# ssh -L 9527:172.16.252.100:23 -fN 172.16.252.157

格式为：ssh -L 本地端口:telnet服务器ip：telnet服务器端口 -fN 转发主机ip 
其中-f指后台运行，-N指不打开新的shell

• 连接远程telnet服务器：

  [root@Shining ~]# telnet 127.0.0.1 9527

• 实现ssh转发telnet

左侧CentOS7：

[root@Shining ~]# ss -tn
State      Recv-Q Send-Q Local Address:Port               Peer Address:Port              
ESTAB      0      52     172.16.253.159:22                 172.16.254.183:7220               
ESTAB      0      0      172.16.254.39:47615              172.16.252.157:22

中间CentOS6：

[root@localhost /etc/yum.repos.d]# ss -tn
State      Recv-Q Send-Q          Local Address:Port            Peer Address:Port 
ESTAB      0      0              172.16.252.157:41111         172.16.252.100:23    
ESTAB      0      0              172.16.252.157:22             172.16.254.39:47615 
ESTAB      0      64             172.16.252.157:22            172.16.254.183:7221

右侧CentOS7：

 [root@Shining ~]# ss -tn
State      Recv-Q Send-Q Local Address:Port               Peer Address:Port              
ESTAB      0      52     172.16.252.100:22                 172.16.254.183:7515               
ESTAB      0      0      ::ffff:172.16.252.100:23                 ::ffff:172.16.252.157:41111

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