linux下ssh端口转发

假设现在有两台服务器client1，client2，他们直接不能直接相互通信，但是他们均能连接上第三台服务器balance，我们可以在client1，client2和balance三台机器之间建立ssh隧道来让client1和client2实现通信。

ssh端口转发有三种实现方式：本地转发，远程转发，和动态转发。

定义简称：发起请求的服务器(简称"startServer")，最终目标服务器(简称“targetServer”)，连接startServer和targetServer的服务器(简称“bridgeServer”)

一. 准备工作

实现目标: startServer能访问bridgeServer但不能直接访问targetServer，bridgeServer可以访问targetServer；startServer通过bridgeServer做端口转发可以间接访问targetServer。

1.1 服务器IP：

startServer：服务器guangzhou-IP  106.55.241.99

targetServer：服务器new2-IP 106.55.171.53

bridgeServer：服务器balance-IP 124.156.143.168

1.2 服务器间通信状态

 服务器guangzhou：

#可访问new2
[root@guangzhou ~]# telnet 106.55.171.53 22
Trying 106.55.171.53...
Connected to 106.55.171.53.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4

#可访问balance
[root@guangzhou ~]# telnet 124.156.143.168 22
Trying 124.156.143.168...
Connected to 124.156.143.168.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4

 服务器balance：

#可访问new2
[root@Balance ~]# telnet 106.55.241.99 22
Trying 106.55.241.99...
Connected to 106.55.241.99.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4

 现在上new2防火墙添加禁止guangzhou访问并重启firewalld服务：

[root@new2 ~]# firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address="106.55.241.99" drop'
success
[root@new2 ~]# firewall-cmd --reload
success 

 登陆guangzhou服务器执行命令: telnet 106.55.171.53 22 ，结果无响应，说明防火墙禁止访问设置成功。

 目前guangzhou无法直连new2，可连接balance，balance可连接new2.

 

二. 配置端口转发

2.1 本地转发

命令：-L localport:remotehost:remotehostport sshserver

说明：localport　　　　　　    本机开启的端口号

         remotehost　　　　　　最终连接机器的IP地址

         remotehostport             转发机器的端口号

         sshserver　　　　　　   转发机器的IP地址

# -L startServerIp:targetServerIp:targetServerPort bridgeServerUser@bridgeServerIp
[root@guangzhou ~]# ssh -L 9001:106.55.171.53:22 root@124.156.143.168
root@124.156.143.168's password:
Last failed login: Thu Oct  8 19:29:00 CST 2020 from 61.135.223.109 on ssh:notty
There were 8 failed login attempts since the last successful login.
Last login: Thu Oct  8 19:26:38 2020 from 106.55.241.99
[root@Balance ~]#

新开窗口打开guangzhou服务器：

[root@guangzhou ~]# ssh -p 9001 root@127.0.0.1
The authenticity of host '[127.0.0.1]:9001 ([127.0.0.1]:9001)' can't be established.
ECDSA key fingerprint is SHA256:huOuuKbfM9TN6+rpCMjB2Hk0HI4GSF1WCj7gIVyu48I.
ECDSA key fingerprint is MD5:0f:55:88:04:62:82:fc:8b:6a:f5:9e:5c:56:e1:0b:cc.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[127.0.0.1]:9001' (ECDSA) to the list of known hosts.
root@127.0.0.1's password:
Last failed login: Thu Oct  8 19:29:28 CST 2020 from 213.154.70.102 on ssh:notty
There were 832 failed login attempts since the last successful login.
Last login: Thu Oct  8 18:41:46 2020 from 106.55.241.99
[root@new2 ~]#

上面可见后面新开窗口通过访问9001端口可以连接上new2服务器。

2.2 远程转发

命令：-R sshserverport:remotehost:remotehostport sshserver

说明：sshserverport           被转发机器开启的端口号

         remotehost       　　 最终连接机器的IP地址

         remotehostport         被转发机器的端口号

         sshserver                 被转发机器的IP地址

#balance服务器上开启端口转发服务
# -R startServerPort:targetServerIp:targetServerPort -fN startServerIp
[root@Balance ~]# ssh -R 9100:106.55.171.53:22  -fN 106.55.241.99
root@106.55.241.99's password:
[root@Balance ~]#

#guangzhou服务器上查看balance端口转发开启的9100端口
[root@guangzhou ~]# ss -ntl
State      Recv-Q Send-Q                    Local Address:Port                                   Peer Address:Port
LISTEN     0      128                                   *:27017                                             *:*
LISTEN     0      511                                   *:6379                                              *:*
LISTEN     0      128                                   *:9100                                              *:*
LISTEN     0      128                                   *:111                                               *:*
LISTEN     0      128                                   *:4369                                              *:*
LISTEN     0      128                                   *:22                                                *:*
LISTEN     0      80                                   :::3306                                             :::*
LISTEN     0      511                                  :::6379                                             :::*
LISTEN     0      128                                  :::111                                              :::*
LISTEN     0      128                                  :::4369                                             :::*
#连接9100端口，确认可以连接上new2服务器
[root@guangzhou ~]# ssh -p 9100 root@127.0.0.1
The authenticity of host '[127.0.0.1]:9100 ([127.0.0.1]:9100)' can't be established.
ECDSA key fingerprint is SHA256:huOuuKbfM9TN6+rpCMjB2Hk0HI4GSF1WCj7gIVyu48I.
ECDSA key fingerprint is MD5:0f:55:88:04:62:82:fc:8b:6a:f5:9e:5c:56:e1:0b:cc.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[127.0.0.1]:9100' (ECDSA) to the list of known hosts.
root@127.0.0.1's password:
Last failed login: Fri Oct  9 11:28:02 CST 2020 from 61.7.235.211 on ssh:notty
There were 3 failed login attempts since the last successful login.
Last login: Fri Oct  9 11:26:16 2020 from 117.136.79.20
[root@new2 ~]#

远程转发就是做了一层请求代理服务，将指定客户端IP和客户端端口的请求转发到指定第三方服务器IP和端口。

2.3动态转发
命令：-D localhost:localport -fN sshserver

# -D startServerPort -fN bridgeServerIp

#guangzhou服务器上关掉所有ssh连接
[root@guangzhou ~]# killall ssh
[root@guangzhou ~]# ssh -D 9200 -fN 124.156.143.168
root@124.156.143.168's password:
[root@guangzhou ~]# curl --socks5 127.0.0.1:9200 http://106.55.171.53
hello~ 

以上通过设置guangzhou服务器9200端口转发已经可以正常请求new2服务器上的web服务。

三. 使用实践

假设guangzhou服务器访问new2服务器的mysql服务，mysql端口为3306，同之前一样new2防火墙增加IP禁止guangzhou访问。

以下是php实现的例子。

#guangzhou服务器使用9001端口通过balance连接new2的3306端口，这里以本地转发为例
[root@guangzhou ~]# ssh -L 9001:106.55.171.53:3306 root@124.156.143.168
root@124.156.143.168's password:
Last failed login: Fri Oct  9 16:10:57 CST 2020 from 124.65.143.22 on ssh:notty
There were 476 failed login attempts since the last successful login.
Last login: Fri Oct  9 15:49:20 2020 from 117.136.79.20

#guangzhou服务器新开窗口mysql命令行链接测试下
[root@guangzhou ~]# mysql -h127.0.0.1 -P9001 -utest1 -p123456
Welcome to the MariaDB monitor.  Commands end with ; or g.
Your MariaDB connection id is 19
Server version: 10.2.31-MariaDB-log MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

MariaDB [(none)]>

[root@guangzhou ~]# cat pdo.php
<?php

$host = "127.0.0.1";
$port = "9001"; 
$username = "root";
$password = "123456";
$dbname = "test";
$charset = "utf8mb4";

$dsn = "mysql:dbname=$dbname;host=$host";

try{
    $pdo = new Pdo($dsn, $username, $password);
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);    // 设置sql语句查询如果出现问题 就会抛出异常
    set_exception_handler("cus_exception_handler");
} catch(PDOException $e){
    die("连接失败: ".$e->getMessage());
}

function cus_exception_handler($e)
{
    die("sql 异常: ".$e->getMessage());
}

//查询数据
$state = $pdo->query("select * from home limit 1");

//  query执行一条SQL语句，如果通过，则返回一个PDOStatement对象,可以直接遍历这个返回的记录集 (query用于select)

$res = $state->fetch(PDO::FETCH_ASSOC);      // 获取结果集中的一行数据

print_r($res);
[root@guangzhou ~]# php pdo.php
Array
(
    [home_id] => 34
    [profile] => test
    [scope] => no
    [product] => no
    [cooperate] => no
    [extension] => n
)

	优点	缺点
本地转发	不用占用bridgeServer机器上新开端口(默认使用22端口)	占用startServer端口，bridgeServer的IP+端口，更换startServer后需要再次执行ssh命令
远程转发	不限制startServer的IP，bridgeServer执行一次可一直使用转发服务	需要bridgeServer持续提供服务的话要启用常住进程，占用bridgeServer机I/O资源
动态转发	不需要bridgeServer提供常住进程服务，无需bridgeServer和targetServer指定端口	需要startServer占用端口，更换startServer后需要再次执行ssh命令

  

总的来说，三种转发各有优缺点，本地转发和远程转发需要时刻保证ssh隧道可用，动态转发则不需要，可以按照自己需求设置即可。

至此，三种ssh端口转发方式实践完毕。