Using SSH Port Forwarding To Build SSH Tunnel On GNU/Linux

出於安全考慮，公司的服務器需通過跳板機(front)主機才能登陸。但在實際操作過程中遇到一些不便之處，如無法直接從本地上傳文件到目標主機。故而想實現在本機通過跳板機直接連接目標主機，實現文件的上傳、下載和命令操作。本文嘗試使用SSH通過跳板主機在本機與目標主機之間建立Tunnel(隧道)，實現遠程連接。相關實現方式可參考What’s ssh port forwarding and what’s the difference between ssh local and remote port forwarding。

Simple Operation

April 26,2019更新，通過如下方式更爲簡單、快捷

在ssh配置文件~/.ssh/config進行如下配置

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# https://infosec.mozilla.org/guidelines/openssh.html
# Directives Explanation Start
# - port forward, execute 'ssh -fNg'
# LocalForward [127.0.0.1:]8080 127.0.0.1:80  --  forward remote host tcp port '80' to local host tcp port '8080' over the secure channel
# RemoteForward [127.0.0.1:]80 127.0.0.1:8080  --  forward local host tcp port '80' to remote host tcp port '8080' over the secure channel
# DynamicForward 127.0.0.1:8888  --  create a socks5 secure channel at local host which socks5 port is '8888', the application protocol is then used to determine where to connect to from the remote machine

# - login internal host via jump host (Host remote_jump_host)
# https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts
# ProxyJump remote_jump_host1[,remote_jump_host2,...]  -- ProxyJump add in OpenSSH 7.3
# ProxyCommand ssh remote_jump_host -W %h:%p %r  -- recommended way if has no ProxyJump
# ProxyCommand ssh remote_jump_host nc %h %p %r  -- need install pack 'nc' in internal host
# ProxyCommand nc -X 5 -x localhost:9050 %h %p    -- SSH over Tor, need install netcat, netcat-openbsd
# Directives Explanation End


# Sample Start
# execute 'ssh sample_internal_host1' to directly login internal host 'sample_internal_host1' via jump host 'sample_jump'
# Host sample_jump
# 	HostName 122.144.200.62
# 	Port 22000
# 	IdentityFile /PATH/jump_key
#
# Host sample_internal_*
# 	#ProxyJump sample_jump
# 	#ProxyCommand ssh sample_jump nc %h %p %r
# 	ProxyCommand ssh sample_jump -W %h:%p %r
#   # /PATH/internal_key is ssh keygen own by host sample_jump
# 	IdentityFile /PATH/internal_key
#
# Host sample_internal_host1
#     HostName 192.168.6.8
#     User user_1
#     Port 22222
# Sample End

例如

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Host digital_ocean
    User root
    HostName 104.131.148.149
    DynamicForward 127.0.0.1:9999
    #LocalForward 127.0.0.1:9050 127.0.0.1:9050
    #LocalForward 127.0.0.1:8080 127.0.0.1:8080

配置完成後，只需執行ssh -fNg digital_ocean即可成功創建端口轉發。

以下內容爲原始內容

Preparation

本文中的所有實驗都在 Digital Ocean 的VPS中進行，因本機使用的是CentOS 7.2，為保證環境一致，故而VPS的操作系統也選擇CentOS 7.2，登陸VPS的SSH Key保存在本地主機用戶家目錄的~/.ssh中。

注意：所有操作都是在root用戶下進行。

SSH的配置和使用可參考本人之前Blog

如何生成SSH-Keygen Key，可參考文中的Generating SSH-Keygen Keys部分。

Environmental Design

本地主機可通過SSH連接遠程主機Front的外網IP，而遠程主機Target則只能與遠程主機Front進行內網通信，即防火牆規則中只允許遠程主機Target的內網IP通過。

先爲遠程主機Target設置root用戶密碼可通過密碼登陸，之後在安裝SSH-Keygen Key，使之可以通過ssh -i免密碼登陸。

Server Info

以下是本地主機、遠程主機的相關信息

本地主機

item	detail
Operating System	`CentOS Linux release 7.2.1511 (Core)`
Kernel Version	`3.10.0-327.28.3.el7.x86_64`
Time Zone	`Asia/Shanghai (CST, +0800)`
OpenSSH Version	`OpenSSH_6.6.1p1`

遠程主機

Machine	Host Name	Outer IP	Inner IP	SSH Port
跳板機	`Front`	`104.131.148.149`	`10.134.5.221`	`22`
目標主機	`Target`	`104.131.150.251`	`10.134.12.148`	`22`

Configuration

遠程主機配置主要包括以下方面

更改遠程主機Front、Target的時區為Asia/Shanghai，安裝chrony服務自動同步時間；
為遠程主機Target設置root密碼，默認是通過SSH Key連接；
在遠程主機Target上安裝iptables防火牆，並設置只允許遠程主機Front訪問主機Target的22號端口；

Digital Ocean的VPS默認SELinux服務被禁用，firewalld服務未啟用，iptables服務未安裝。

Front & Target

分別在遠程主機Front、Target中執行如下命令

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# 禁用SELinux
sed -i -r '[email protected][email protected][email protected];[email protected](SELINUXTYPE=targeted)@#\[email protected]' /etc/selinux/config
setenforce 0

# 關閉firewalld
systemctl stop firewalld
systemctl disable firewalld

#設置時區
timedatectl set-timezone Asia/Shanghai

#安裝chrony服務並啟用
yum install -y chrony
systemctl start chronyd
systemctl enable chronyd

操作完成後可通過timedatectl命令查看時區信息，信息顯示如下

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# Front
[[email protected] ~]# timedatectl
      Local time: Fri 2016-08-26 09:08:20 CST
  Universal time: Fri 2016-08-26 01:08:20 UTC
        RTC time: Fri 2016-08-26 09:08:20
       Time zone: Asia/Shanghai (CST, +0800)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: yes
      DST active: n/a

Warning: The system is configured to read the RTC time in the local time zone.
         This mode can not be fully supported. It will create various problems
         with time zone changes and daylight saving time adjustments. The RTC
         time is never updated, it relies on external facilities to maintain it.
         If at all possible, use RTC in UTC by calling
         'timedatectl set-local-rtc 0'.
[[email protected] ~]#


# Target
[[email protected] ~]# timedatectl
      Local time: Fri 2016-08-26 09:08:26 CST
  Universal time: Fri 2016-08-26 01:08:26 UTC
        RTC time: Fri 2016-08-26 09:08:25
       Time zone: Asia/Shanghai (CST, +0800)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: yes
      DST active: n/a

Warning: The system is configured to read the RTC time in the local time zone.
         This mode can not be fully supported. It will create various problems
         with time zone changes and daylight saving time adjustments. The RTC
         time is never updated, it relies on external facilities to maintain it.
         If at all possible, use RTC in UTC by calling
         'timedatectl set-local-rtc 0'.
[[email protected] ~]#

Target Only

在遠程主機Target中執行如下命令

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# 設置root密碼為 axdlog.com
echo "axdlog.com" | passwd --stdin root

#安裝、啓用iptables服務，並添加規則
yum install -y iptables iptables-services
systemctl start iptables

#查看現有的規則
iptables -L -n

# 關閉iptables服務
systemctl stop iptables

#清除已有規則
iptables -F
iptables -X
iptables -Z

# 保存規則
service iptables save

#只允許遠程主機Front的內網IP通信
iptables -A INPUT -s 10.134.5.221 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -d 10.134.5.221 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

#保證yum服務能正常使用
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -m udp --sport 53 -j ACCEPT
iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p udp -m udp --dport 53 -j ACCEPT

#關閉所有端口(因是通過SSH連接修改iptable規則，如果執行會導致SSH連接斷開)
# iptables -P INPUT DROP
# iptables -P OUTPUT DROP
# iptables -P FORWARD DROP

#保存規則
service iptables save

#重啟iptables服務
systemctl restart iptables

再次嘗試從本地主機連接遠程主機Target已經無法連接

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[[email protected] ~]$ ssh [email protected]
ssh: connect to host 104.131.150.251 port 22: Connection timed out
[[email protected] ~]$

從遠程主機Front可通過遠程主機Target的內網IP進行連接

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[[email protected] ~]# ssh [email protected]
The authenticity of host '10.134.12.148 (10.134.12.148)' can't be established.
ECDSA key fingerprint is 7b:39:56:00:5b:ff:f6:b2:b6:53:7f:3c:c7:7b:6b:f0.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '10.134.12.148' (ECDSA) to the list of known hosts.
[email protected]'s password:
Last failed login: Fri Aug 26 09:23:42 CST 2016 from 220.181.167.182 on ssh:notty
There were 9 failed login attempts since the last successful login.
Last login: Fri Aug 26 09:12:19 2016 from 10.134.5.221
[[email protected] ~]# hostname
Target
[[email protected] ~]# exit
logout
Connection to 10.134.12.148 closed.
[[email protected] ~]# exit
logout
Connection to 104.131.148.149 closed.
[[email protected] ~]$

Port Forwarding

SSH端口轉發主要分為三種

Local Port Forwarding
Remote Port Forwarding
Dynamic Port Forwarding

具體的命令形式

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# Local Port Forwarding
ssh -C -f -N -g -L 127.0.0.1:6666:10.134.12.148:22 -p 22 -i ~/.ssh/id_rsa [email protected]

# Remote Port Forwarding
ssh -C -f -N -g -R 127.0.0.1:7777:10.134.12.148:22 -p 22 -i ~/.ssh/id_rsa [email protected]

# Dynamic Port Forwarding
ssh -C -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected]  2>/dev/null

相關參數解釋

-C: Requests compression of all data (including stdin, stdout, stderr, and data for forwarded X11 and TCP connections).
-f: Requests ssh to go to background just before command execution.
-N: Do not execute a remote command (protocol version 2 only).
-g: Allows remote hosts to connect to local forwarded ports.
-L [bind_address:]port:host:hostport: Specifies that the given port on the local (client) host is to be forwarded to the given host and port on the remote side.
-R [bind_address:]port:host:hostport: Specifies that the given port on the remote (server) host is to be forwarded to the given host and port on the local side.
-D [bind_address:]port: Specifies a local “dynamic” application-level port forwarding.
-i identity_file: Selects a file from which the identity (private key) for public key authentication is read.
-p port: Port to connect to on the remote host.

注意：tunnel(隧道)的建立需要一定時間，請耐心等待。

Local Port Forwarding

Using Password

執行如下命令，會在本地主機上創建端口號為6666的端口，將該端口號的數據通過Front(104.131.148.149)轉發到Target內網IP(10.134.12.148)的22號端口。

執行如下命令建立SSH Tunnel實現本地端口轉發

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# Local Port Forwarding
ssh -C -f -N -g -L 127.0.0.1:6666:10.134.12.148:22 -p 22 -i ~/.ssh/id_rsa [email protected]

在本地主機執行如下命令

`1`	`ssh -p 6666 [email protected]`

即可正常登陸遠程主機Target

以下是操作過程

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[[email protected] ~]$ ssh -p 6666 [email protected]
The authenticity of host '[127.0.0.1]:6666 ([127.0.0.1]:6666)' can't be established.
ECDSA key fingerprint is 7b:39:56:00:5b:ff:f6:b2:b6:53:7f:3c:c7:7b:6b:f0.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[127.0.0.1]:6666' (ECDSA) to the list of known hosts.
Last login: Fri Aug 26 09:28:12 2016 from 10.134.5.221
[[email protected] ~]# hostnamectl
   Static hostname: target
   Pretty hostname: Target
Transient hostname: Target
         Icon name: computer-vm
           Chassis: vm
        Machine ID: c3f4abf4b4024198ade2d41e6f26652d
           Boot ID: a890b11a7cc84ec9b6a63359ac21a014
    Virtualization: kvm
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-327.28.2.el7.x86_64
      Architecture: x86-64
[[email protected] ~]# echo 'This is Target Host' > /tmp/hostInfo.txt
[[email protected] ~]# cat /tmp/hostInfo.txt
This is Target Host
[[email protected] ~]# exit
logout
Connection to 127.0.0.1 closed.
[[email protected] ~]$

在遠程主機Target的/tmp下創建文件hostInfo.txt，內容為This is Target Host。

注：可使用如下命令在本地主機查看端口6666相關信息

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ss -tnl | grep 6666

ps -ef | awk '$0~/6666/&&$0!~/grep/'

sudo netstat -apn | awk '$0~/6666/&&$0~/LISTEN/'

# 獲取父進程信息
ps -ef | grep `sudo netstat -apn | awk '$0~/6666/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'`

# 獲取父進程ID
ps -ef | grep `sudo netstat -apn | awk '$0~/6666/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'` | awk '{print $2}'

# 通過Kill命令終止父進程實現該端口的關閉
ps -ef | grep `sudo netstat -apn | awk '$0~/6666/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'` | awk '{print $2}' | xargs kill -s 9

SFTP Connection

通過sftp連接遠程主機Target

sftp命令格式如下

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sftp [-1246aCfpqrv] [-B buffer_size] [-b batchfile] [-c cipher] [-D sftp_server_path] [-F ssh_config]
          [-i identity_file] [-l limit] [-o ssh_option] [-P port] [-R num_requests] [-S program]
          [-s subsystem | sftp_server] host
sftp [[email protected]]host[:file ...]
sftp [[email protected]]host[:dir[/]]
sftp -b batchfile [[email protected]]host

注意：指定端口在ssh命令中是小寫字母-p，而在sftp中是大寫字母-P；

執行如下命令即可以ftp形式進入遠程主機Target

`1`	`sftp -P 6666 [email protected]`

操作過程

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[[email protected] ~]$ sftp -P 6666 [email protected]
Connected to 127.0.0.1.
sftp> cd /tmp/
sftp> ls
hostInfo.txt    
sftp> exit
[[email protected] ~]$

get data

在stfp中使用get命令可將遠程主機中的文件下載到本地主機

命令格式

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get [-afPpr] remote-path [local-path]

Retrieve the remote-path and store it on the local machine. If the local path name is not specified, it is given the same name it has on the remote machine. remote-path may contain glob(3) characters and may match multiple files. If it does and local-path is specified, then local-path must specify a directory.

此處將文件hostInfo.txt下載到本地主機的/tmp目錄下，並更名爲SaveToLocalHost.txt，操作過程

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[[email protected] ~]$ ls -lh /tmp/SaveToLocalHost.txt
ls: cannot access /tmp/SaveToLocalHost.txt: No such file or directory
[[email protected] ~]$ sftp -P 6666 [email protected]
Connected to 127.0.0.1.
sftp> cd /tmp/
sftp> ls
hostInfo.txt    
sftp> get hostInfo.txt /tmp/SaveToLocalHost.txt
Fetching /tmp/hostInfo.txt to /tmp/SaveToLocalHost.txt
/tmp/hostInfo.txt                             100%   20     0.0KB/s   00:00    
sftp> exit
[[email protected] ~]$ cat /tmp/SaveToLocalHost.txt
This is Target Host
[[email protected] ~]$

put data

在stfp中使用put命令可將本地主機中的文件上傳到遠程主機中

命令格式

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put [-fPpr] local-path [remote-path]

Upload local-path and store it on the remote machine. If the remote path name is not specified, it is given the same name it has on the local machine. local-path may contain glob(3) characters and may match multiple files. If it does and remote-path is specified, then remote-path must specify a directory.

此處將本地主機目錄/home/flying/Downloads中的文件Linux From Scratch-Version7.9.pdf上傳到遠程主機的/tmp目錄下，操作過程

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[[email protected] ~]$ namei -l ~/Downloads/Linux\ From\ Scratch-Version7.9.pdf
f: /home/flying/Downloads/Linux From Scratch-Version7.9.pdf
dr-xr-xr-x root   root   /
drwxr-xr-x root   root   home
drwx------ flying flying flying
drwxr-xr-x flying flying Downloads
-rw-rw-r-- flying flying Linux From Scratch-Version7.9.pdf
[[email protected] ~]$ sftp -P 6666 [email protected] to 127.0.0.1.
sftp> cd /tmp/
sftp> ls
hostInfo.txt    
sftp> put /home/flying/Downloads/Linux\ From\ Scratch-Version7.9.pdf /tmp
Uploading /home/flying/Downloads/Linux From Scratch-Version7.9.pdf to /tmp/Linux From Scratch-Version7.9.pdf
/home/flying/Downloads/Linux From Scratch-Ver 100% 1696KB 106.0KB/s   00:16    
sftp> ls
Linux From Scratch-Version7.9.pdf       hostInfo.txt                            
sftp> exit
[[email protected] ~]$

Using SSH-Keygen Key

重要：如果遠程主機Front是通過SSH Key形式連接遠程主機Target，則在連接時，命令ssh -p 6666 [email protected]是無法連接成功的，可添加參數-vvv查看具體信息。它需要的是跳板機Front的私鑰。故而需將遠程主機Front目錄/root/.ssh/下的id_rsa(私鑰)、id_rsa.pub(公鑰)保存到本地主機中，且文件讀寫權限設置為600，然後通過參數-i指定，形式如下

`1`	`ssh -p 6666 -i /LOCALHOST/PATH/Front/id_rsa [email protected]`

這樣才能正常登入遠程主機Target

在遠程主機Front中執行如下命令，創建SSH-Keygen並安裝到遠程主機Target中

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# 生成密鑰，設置passphrase爲 grepsedawk
ssh-keygen -t rsa -b 4096 -C 'SSH Tunnel Testing'

# 安裝ssh-keygen key
ssh-copy-id -i ~/.ssh/id_rsa.pub -p 22 [email protected]
#或執行該命令
cat ~/.ssh/id_rsa.pub | ssh -p 22 [email protected] 'umask 077; test -d .ssh|| mkdir .ssh; cat >> .ssh/authorized_keys'

操作過程

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[[email protected] ~]$ ssh [email protected]
Last failed login: Fri Aug 26 09:55:00 CST 2016 from 116.31.116.8 on ssh:notty
There were 12 failed login attempts since the last successful login.
Last login: Fri Aug 26 09:52:32 2016 from 116.228.89.242
[[email protected] ~]# ssh-keygen -t rsa -b 4096 -C 'SSH Tunnel Testing'
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):

#指定passphrase，相當於爲ssh-keygen key再加一層安全保護
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
ca:1c:f6:bb:2a:34:e9:09:03:83:ca:e4:4c:3f:95:4a SSH Tunnel Testing
The key's randomart image is:
+--[ RSA 4096]----+
|                 |
|                 |
|.     .          |
|+o E o           |
|Boo o.o S        |
|.+o+++ +         |
|   =.o+ .        |
|    +    .       |
|     ...o.       |
+-----------------+
[[email protected] ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub -p 22 [email protected]
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
[email protected]'s password:
# 此處輸入的是遠程主機Target的root用戶的登陸密碼

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh -p '22' '[email protected]'"
and check to make sure that only the key(s) you wanted were added.

#此處輸入的是創建ssh-keygen時設置的passphrase
[[email protected] ~]# ssh -p 22 [email protected]
Enter passphrase for key '/root/.ssh/id_rsa':
Last login: Fri Aug 26 09:35:57 2016 from 10.134.5.221
[[email protected] ~]# tail -1 ~/.ssh/authorized_keys
ssh-rsa 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 LempStacker.com SSH Tunnel Testing
[[email protected] ~]# exit
logout
Connection to 10.134.12.148 closed.
[[email protected] ~]# exit
logout
Connection to 104.131.148.149 closed.
[[email protected] ~]$

將遠程主機Front目錄~/.ssh中的密鑰文件下載到本地主機中，以保存到目錄/tmp/front中爲例

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[[email protected] ~]$ mkdir /tmp/front
[[email protected] ~]$ sftp -P 22 [email protected]
Connected to 104.131.148.149.
sftp> cd .ssh/
sftp> ls
authorized_keys     id_rsa              id_rsa.pub          known_hosts         
sftp> get id
id_rsa       id_rsa.pub
sftp> get id_rsa /tmp/front/
Fetching /root/.ssh/id_rsa to /tmp/front/id_rsa
/root/.ssh/id_rsa                             100% 3326     3.3KB/s   00:01    
sftp> get id_rsa.pub /tmp/front/
Fetching /root/.ssh/id_rsa.pub to /tmp/front/id_rsa.pub
/root/.ssh/id_rsa.pub                         100%  760     0.7KB/s   00:00    
sftp> exit
[[email protected] ~]$ ls -lh /tmp/front/
total 8.0K
-rw------- 1 flying flying 3.3K Aug 26 10:16 id_rsa
-rw-r--r-- 1 flying flying  760 Aug 26 10:16 id_rsa.pub

#修改文件讀寫權限爲600
[[email protected] ~]$ chmod 600 /tmp/front/id_rsa*
[[email protected] ~]$ ls -lh /tmp/front/
total 8.0K
-rw------- 1 flying flying 3.3K Aug 26 10:16 id_rsa
-rw------- 1 flying flying  760 Aug 26 10:16 id_rsa.pub
[[email protected] ~]$

執行如下命令kill使用端口6666的進程

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ps -ef | grep `sudo netstat -apn | awk '$0~/6666/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'` | awk '{print $2}' | xargs kill -s 9

再次執行如下命令創建SSH Tunnel

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# Local Port Forwarding
ssh -C -f -N -g -L 127.0.0.1:6666:10.134.12.148:22 -p 22 -i ~/.ssh/id_rsa [email protected]

root password

在本地主機執行如下命令,會要求輸入root用戶密碼，才能正常登陸遠程主機Target

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ssh -p 6666 [email protected]

sftp -P 6666 [email protected]

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[[email protected] ~]$ ssh -p 6666 [email protected]
[email protected]'s password:
Last failed login: Fri Aug 26 10:33:47 CST 2016 from 10.134.5.221 on ssh:notty
There was 1 failed login attempt since the last successful login.
Last login: Fri Aug 26 10:29:20 2016 from 10.134.5.221
[[email protected] ~]# hostname
Target
[[email protected] ~]# exit
logout
Connection to 127.0.0.1 closed.
[[email protected] ~]$

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[[email protected] ~]$ sftp -P 6666 [email protected]
[email protected]'s password:
Connected to 127.0.0.1.
sftp> exit
[[email protected] ~]$

ssh-keygen key

在本地主機執行如下命令,指定從遠程主機Front下載下來的ssh-keygen key，會要求輸入passphrase密碼，才能正常登陸遠程主機Target

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ssh -p 6666 -i /tmp/front/id_rsa [email protected]

sftp -P 6666 -i /tmp/front/id_rsa [email protected]

操作過程

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[[email protected] ~]$ ssh -p 6666 -i /tmp/front/id_rsa [email protected]
Enter passphrase for key '/tmp/front/id_rsa':
Last login: Fri Aug 26 10:34:54 2016 from 10.134.5.221
[[email protected] ~]# exit
logout
Connection to 127.0.0.1 closed.
[[email protected] ~]$ sftp -P 6666 -i /tmp/front/id_rsa [email protected]
Enter passphrase for key '/tmp/front/id_rsa':
Connected to 127.0.0.1.
sftp> exit
[[email protected] ~]$

Actual Case

遠程主機Target是內網主機，只有遠程主機Front能與之連接通信，本地主機可以連接遠程主機Front。在遠程主機Target中安裝Nginx服務，並設置只允許遠程主機Front能訪問80端口。現通過遠程主機Front建立SSH Tunnel，將遠程主機Target的80端口映射到本地主機的8080端口，實現在本地瀏覽器URL中輸入http://localhost:8080/即可訪問遠程主機Target的Web服務。

Preparation

在遠程主機Front中執行如下操作

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# 安裝epel源
yum install -y epel-release

# 安裝epel源後安裝Nginx，在epel源中
yum install -y nginx

# 啓動Nginx服務
systemctl start nginx

# 查看80端口是否啓用
ss -tnl | grep -w 80

# 添加iptables規則
iptables -A INPUT -s 10.134.5.221/32 -p tcp -m tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -d 10.134.5.221/32 -p tcp -m tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

# 保存iptables規則
service iptables save

# 創建Web頁面
tee /usr/share/nginx/html/index.html <<-'EOF'
<h1>This is Target Host <strong>axdlog.com</strong> on CentOS 7!</h1>
EOF

在本地主機中執行如下命令創建SSH Tunnel

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ssh -C -c aes256-ctr -o StrictHostKeyChecking=no -f -N -g -L 127.0.0.1:7777:10.134.12.148:80 -p 22 -i ~/.ssh/id_rsa [email protected]

Operation Process

在遠程主機Front中可以正常訪問該服務

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[[email protected] ~]# curl http://10.134.12.148:80
<h1>This is Target Host <strong>axdlog.com</strong> on CentOS 7!</h1>
[[email protected] ~]# curl -I http://10.134.12.148:80
HTTP/1.1 200 OK
Server: nginx/1.6.3
Date: Fri, 26 Aug 2016 07:31:21 GMT
Content-Type: text/html
Content-Length: 75
Last-Modified: Fri, 26 Aug 2016 07:29:13 GMT
Connection: keep-alive
ETag: "57bfefc9-4b"
Accept-Ranges: bytes

[[email protected] ~]#

在本地主機使用127.0.0.1:7777

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[[email protected] ~]$ curl http://127.0.0.1:7777
<h1>This is Target Host <strong>axdlog.com</strong> on CentOS 7!</h1>
[[email protected] ~]$ curl -I http://127.0.0.1:7777
HTTP/1.1 200 OK
Server: nginx/1.6.3
Date: Fri, 26 Aug 2016 07:37:00 GMT
Content-Type: text/html
Content-Length: 75
Last-Modified: Fri, 26 Aug 2016 07:29:13 GMT
Connection: keep-alive
ETag: "57bfefc9-4b"
Accept-Ranges: bytes

[[email protected] ~]$

可以看到在本機能正常訪問遠程主機FrontWeb服務中的內容。

Remote Port Forwarding

~~遠程端口轉發尚未完全理解，暫時擱置~~

本地主機可通過外網IP連接遠程主機Front，遠程主機Target可連接遠程主機Front，但遠程主機Front無法直接連接本地主機。即本地主機和遠程主機Target都沒有公網IP，但都能連接遠程主機Front。

Scenario 1

情境設置：我在自己電腦的本地開發環境中開發了一個項目，想給外地的客戶或朋友看，他們無法直接在我電腦上看。但是我有一臺有獨立外網IP的VPS，我可以在自己的電腦上通過SSH創建遠程端口轉發，將本地的80端口的數據轉發到VPS(104.131.148.149)上的指定端口7777。身在外地的客戶或朋友直接在瀏覽器中輸入http://104.131.148.149:7777即可看到我電腦上的Web項目。

重要：使用遠程主機進行端口轉發，必須在VPS的/etc/ssh/sshd_config文件中設置

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GatewayPorts yes

然後執行如下命令重啓sshd服務

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systemctl restart ssh
# systemctl restart sshd

在本地主機執行如下命令

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ssh -C  -c aes256-ctr -o StrictHostKeyChecking=no -f -N -g -R 7777:127.0.0.1:80 -p 22 -i ~/.ssh/id_rsa [email protected]

在遠程主機Target中即可查到已經監聽了7777端口。

測試過程

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[[email protected] ~]$ cat /usr/share/nginx/html/index.html
This is Local Host. axdlog.com
[[email protected] ~]$ curl http://104.131.148.149:7777/
This is Local Host. axdlog.com
[[email protected] ~]$ curl -I http://104.131.148.149:7777/
HTTP/1.1 200 OK
Server: nginx
Date: Fri, 26 Aug 2016 11:20:36 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 36
Last-Modified: Fri, 26 Aug 2016 11:20:07 GMT
Connection: keep-alive
ETag: "57c025e7-24"
Accept-Ranges: bytes

[[email protected] ~]$

Scenario 2

情景設置：兩臺分處於不同地域的主機，主機無獨立IP，通過路由器分配內網地址聯網。如果一臺主機A想通過SSH連接到另一臺主機B，因彼此無獨立IP，無法直接連接，可通過VPS實現。

將VPS中/etc/ssh/sshd_config的GatewayPorts指令設置爲yes，若文件內無該指令，在末尾添加即可，重啓sshd服務。

VPS主機的IP爲104.131.148.149，登錄用戶名爲user_vps，SSH爲的33333號端口。主機B的SSH端口爲22222，登錄用戶名爲user_b。

在主機B中執行如下命令，在VPS中創建遠程端口，此處假設要創建的端口號爲1080。

`1`	`ssh -f -N -g -R 1080:127.0.0.1:22222 -p 33333 [email protected]`

在VPS中通過ss -tnl查看端口1080是否已經監聽。如果已經監聽，在主機A中執行如下命令登錄主機B

`1`	`ssh -p 1080 [email protected]`

注意：執行該命令時，指定的端口號爲創建的遠程轉發端口1080，用戶名是主機B的用戶名user_b，而主機IP則是VPS的主機。

如果啓用了防火牆，須對該遠程轉發端口進行放行。

Dynamic Port Forwarding

-D [bind_address:]port: Specifies a local “dynamic” application-level port forwarding.

在本地主機執行如下命令，為本地主機指定一個本地的動態的應用程序級別的端口轉發，端口號是8888，所有從此端口發出的數據都會轉發到遠程主機Front的22號端口中，可成功穿越firewall。

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# Dynamic Port Forwarding
ssh -C -c aes256-ctr -o StrictHostKeyChecking=0 -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected]  2>/dev/null

在系統或瀏覽器代理中設置Socks Host：主機127.0.0.1，端口號8888，即可實現全局代理。在瀏覽器中查看，此時本機的IP已經變成遠程主機Front的IP(104.131.148.149)。

重要：如果想在後臺執行該命令，可通過setsid或nohup命令實現，具體命令爲

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#setsid
ssh -C -c aes256-ctr -o StrictHostKeyChecking=no -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected] | setsid 2>/dev/null

#nohup
nohup ssh -C -c aes256-ctr -o StrictHostKeyChecking=no -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected] 2> /dev/null &

注：可使用如下命令在本地主機查看端口8888相關信息

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ss -tnlp | grep 8888

ps -ef | awk '$0~/8888/&&$0!~/grep/'

sudo netstat -apn | awk '$0~/8888/&&$0~/LISTEN/'

# 獲取父進程信息
ps -ef | grep `sudo netstat -apn | awk '$0~/8888/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'`

# 獲取父進程ID
ps -ef | grep `sudo netstat -apn | awk '$0~/8888/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'` | awk '{print $2}'

ss -tnlp | awk 'match($4,/8888/){print gensub(/.*,pid=(.*),.*/,"\\1"," ",$6)}'


# 終止父進程
ps -ef | grep `sudo netstat -apn | awk '$0~/8888/&&$0~/LISTEN/{print $NF}' | awk -v FS='/' '{print $1}'` | awk '{print $2}' | xargs kill -s 9

ss -tnlp | awk 'match($4,/8888/){print gensub(/.*,pid=(.*),.*/,"\\1"," ",$6)}' | xargs kill -s 9

Error Occurring

Error 1 (未解決)

執行

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# Dynamic Port Forwarding
ssh -C -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected]

建立Dynamic Port Forwarding後，使用本地IP和Port進行全局代理上網，使用瀏覽器時，CLI中會報如下錯誤信息

open failed: administratively prohibited: open failed

參考

修改遠程主機/etc/ssh/sshd_config中的參數AllowTcpForwarding、GatewayPorts爲yes，但無效，仍舊報錯。

最後只能參考

how to solve the “open failed: administratively prohibited: open failed” when using a SSH tunnel proxy

將報錯信息寫入/dev/null，即命令更改成

`1`	`ssh -C -f -N -g -D 127.0.0.1:8888 -p 22 -i ~/.ssh/id_rsa [email protected] 2>/dev/null`

References

Change Logs

2016.08.26 00:55 Fri Asia/Shanghai
- 初稿完成
2016.08.26 19:35 Fri Asia/Shanghai
- 完善實驗過程
2016.10.18 10:05 Tue Asia/Shanghai
- 添加setsid實現後臺執行
2017.07.14 16:58 Fri Asia/Shanghai
- 爲Remote PortForwarding添加Scenario2，實現SSH連接彼此無獨立IP，但能連接外網的主機
2017.09.09 19:01 Sat Asia/Shanghai
- 添加How to understand SSH perfectly?
2019.04.26 16:50 Fri America/Boston
- 勘誤，添加Simple Operation一節

Table of Contents

Simple Operation

Preparation

Environmental Design

Server Info

Configuration

Front & Target

Target Only

Port Forwarding

Local Port Forwarding

Using Password

SFTP Connection

get data

put data

Using SSH-Keygen Key

root password

ssh-keygen key

Actual Case

Preparation

Operation Process

Remote Port Forwarding

Scenario 1

Scenario 2

Dynamic Port Forwarding

Error Occurring

Error 1 (未解決)

References

Change Logs