假設現在有兩台服務器client1，client2，他們直接不能直接相互通信，但是他們均能連接上第三台服務器balance，我們可以在client1，client2和balance三台機器之間建立ssh隧道來讓client1和client2實現通信。
ssh端口轉發有三種實現方式：本地轉發，遠程轉發，和動態轉發。
定義簡稱：發起請求的服務器(簡稱"startServer")，最終目標服務器(簡稱“targetServer”)，連接startServer和targetServer的服務器(簡稱“bridgeServer”)
一. 准備工作
實現目標: startServer能訪問bridgeServer但不能直接訪問targetServer，bridgeServer可以訪問targetServer；startServer通過bridgeServer做端口轉發可以間接訪問targetServer。
1.1 服務器IP：
startServer：服務器guangzhou-IP 106.55.241.99
targetServer：服務器new2-IP 106.55.171.53
bridgeServer：服務器balance-IP 124.156.143.168
1.2 服務器間通信狀態
服務器guangzhou：
#可訪問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 #可訪問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
服務器balance：
#可訪問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
現在上new2防火牆添加禁止guangzhou訪問並重啟firewalld服務：
[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
登陸guangzhou服務器執行命令: telnet 106.55.171.53 22 ，結果無響應，說明防火牆禁止訪問設置成功。
目前guangzhou無法直連new2，可連接balance，balance可連接new2.
二. 配置端口轉發
2.1 本地轉發
命令：-L localport:remotehost:remotehostport sshserver
說明：localport 本機開啟的端口號
remotehost 最終連接機器的IP地址
remotehostport 轉發機器的端口號
sshserver 轉發機器的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 ~]#
新開窗口打開guangzhou服務器：
[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 ~]#
上面可見后面新開窗口通過訪問9001端口可以連接上new2服務器。
2.2 遠程轉發
命令：-R sshserverport:remotehost:remotehostport sshserver
說明：sshserverport 被轉發機器開啟的端口號
remotehost 最終連接機器的IP地址
remotehostport 被轉發機器的端口號
sshserver 被轉發機器的IP地址
#balance服務器上開啟端口轉發服務
# -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服務器上查看balance端口轉發開啟的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 :::* #連接9100端口，確認可以連接上new2服務器
[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 ~]#
遠程轉發就是做了一層請求代理服務，將指定客戶端IP和客戶端端口的請求轉發到指定第三方服務器IP和端口。
2.3動態轉發
命令：-D localhost:localport -fN sshserver
# -D startServerPort -fN bridgeServerIp
#guangzhou服務器上關掉所有ssh連接
[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~
以上通過設置guangzhou服務器9200端口轉發已經可以正常請求new2服務器上的web服務。
三. 使用實踐
假設guangzhou服務器訪問new2服務器的mysql服務，mysql端口為3306，同之前一樣new2防火牆增加IP禁止guangzhou訪問。
以下是php實現的例子。
#guangzhou服務器使用9001端口通過balance連接new2的3306端口，這里以本地轉發為例
[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服務器新開窗口mysql命令行鏈接測試下
[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); // 設置sql語句查詢如果出現問題 就會拋出異常 set_exception_handler("cus_exception_handler"); } catch(PDOException $e){ die("連接失敗: ".$e->getMessage()); } function cus_exception_handler($e) { die("sql 異常: ".$e->getMessage()); } //查詢數據 $state = $pdo->query("select * from home limit 1"); // query執行一條SQL語句，如果通過，則返回一個PDOStatement對象,可以直接遍歷這個返回的記錄集 (query用於select) $res = $state->fetch(PDO::FETCH_ASSOC); // 獲取結果集中的一行數據 print_r($res); [root@guangzhou ~]# php pdo.php Array ( [home_id] => 34 [profile] => test [scope] => no [product] => no [cooperate] => no [extension] => n )
| 優點 | 缺點 | |
| 本地轉發 | 不用占用bridgeServer機器上新開端口(默認使用22端口) | 占用startServer端口，bridgeServer的IP+端口，更換startServer后需要再次執行ssh命令 |
| 遠程轉發 | 不限制startServer的IP，bridgeServer執行一次可一直使用轉發服務 | 需要bridgeServer持續提供服務的話要啟用常住進程，占用bridgeServer機I/O資源 |
| 動態轉發 | 不需要bridgeServer提供常住進程服務，無需bridgeServer和targetServer指定端口 | 需要startServer占用端口，更換startServer后需要再次執行ssh命令 |
總的來說，三種轉發各有優缺點，本地轉發和遠程轉發需要時刻保證ssh隧道可用，動態轉發則不需要，可以按照自己需求設置即可。
至此，三種ssh端口轉發方式實踐完畢。