![]() ![]() ![]() -f is optional, requests ssh to go to background just before command execution.This is useful for just forwarding ports. -N is optional, tells ssh to not execute a remote command.You could also use localhost in place of 127.0.0.1, assuming you haven’t modified that entry in your /etc/hosts file. Any connections to 127.0.0.1 on port 4001 will be forwarded to 192.168.20.10 on port 22 through the SSH tunnel. Typically, this will be 22, however there could be some security controls in place that do not allow SSH on the common port. It tells ssh to establish the tunnel on the remote port (destination port) 20622. 172.18.50.100 is the SSH server that we will be connecting to.username is the username to log into the jump host.ssh is the command we are using for our ssh tunnel.Access a network device/server that is only accessible via a jumphost You specify a local port for SSH to listen on, such as 4001, and all connections destined for port 4001 will be tunneled via SSH to a specified remote port, such as 22. What is an SSH Tunnel?Īn ssh tunnel aka ssh port forwarding, allows an encrypted tunnel to be established over an untrusted network between an SSH Client and SSH server. However, as long as you have access to the jumphost, you may be able to use an ssh tunnel to mimic being directly connected to a network with access to the otherwise inaccessible hosts. Now, create this script as hosta:/home/tunnel/check_ssh_tunnel.Do you have a network device or server that can only be reached behind a jumphost? This is not an uncommon scenario, as security best practice often requires such. You might also set some SSH options like the destination port in ~/.ssh/config. Depending on your configuration, you might need to allow the user ‘tunnel’ in /etc/ssh/sshd_config. ssh/authorized_keys # Now paste in the public key for this point you should be able to ssh from to without using a password. Ssh-rsa blahAAAAB3NzaC1yc2EAAAABIwAAAQEA.6BEKKCxTIxgBqjLP create a ‘tunnel’ user on Host B and save the public key for in the authorized_keys file ~]# useradd -d /home/tunnel ~]# passwd tunnel # Set a strong ~]# su - ~]# mkdir ~]# vi. Your public key has been saved in /home/tunnel/.ssh/id_rsa.pub.Ħf:30:b8:e1:36:49:74:b9:32:68:6e:bf:3e:62:d3:c2 cat out the id_rsa.pub file which contains the public key that we will need to put on host b: ~]# cat /.ssh/id_rsa.pub Your identification has been saved in /home/tunnel/.ssh/id_rsa. Now create a public/private key pair: ~]$ ssh-keygenĮnter file in which to save the key (/home/tunnel/.ssh/id_rsa): # hit enter to accept the defaultĮnter passphrase (empty for no passphrase): # don't use a passphrase I’ll refer to the box that initiates the connection as Host A, and the box that we connect to as Host B.Ĭreate a ‘tunnel’ user on Host A: ~]# useradd -d /home/tunnel ~]# passwd tunnel # Set a strong ~]# su - tunnel # Become the user 'tunnel' SSH allows you to map both local and remote ports, so it doesn’t really matter which end of the connection you choose to initiate the connection. That user will then be used to create the tunnel and run a script via cron to ensure that it remains up.įirst, select one of the servers that will initiate the SSH connection. The steps described here will create an unprivileged user named ‘tunnel’ on each server. ![]() The SSH commands for port forwarding can be found in the ssh man page. Google can identify plenty of resources regarding the fundamental SSH commands for port forwarding but I didn’t ever find a good resource for setting up a connection and ensuring that it remains active, which is what I hope to provide here. My need was to allow regular non-encrypted MySQL connections over an encrypted tunnel, but there could be many other uses as well. I recently had a need to create a permanent SSH tunnel between Linux servers. ![]()
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