The gateway encrypts this response and sends it back to the client encapsulated in the SSH protocol (TCP 22). The remote server thinks it is receiving a request from the SSH Gateway and responds to it. The SSH gateway decrypts the communication and forwards it to the remote server on TCP port 80 (per the option remoteserver:80). The SSH client software intercepts this call and sends it down the encrypted tunnel to the SSH gateway. To connect to the remote server, the client opens their web browser and connects to This instructs the browser to connect to the client machine on port 8080, which is the endpoint that the SSH client application is listening for new connections. the SSH client is now silently listening for new connections on port 8080. The SSH gateway authenticates the user (in our example, username) and establishes a secure, encrypted channel between the client and SSH gateway.īehind the scenes. Ssh -L 8080:remoteserver:80 you run this command on an internet-connected client, it will connect to the external IP address of the firewall (noted in the option above as FirewallExternalInterfaceIP) on SSH (by default TCP port 22), which forwards the SSH traffic to the SSH gateway. ![]() To connect to a remote server, the command looks like: Generally, the OpenSSH server software does not need any special configuration, either.įigure 1: Simple configuration of SSH local port forwarding. In many cases, no other firewall rules are needed and there is no additional port forwarding required. You must configure the firewall to forward SSH network traffic to the device running SSH server software, also called an SSH daemon. In this example, a client connects to a firewall that forwards SSH connections to an SSH gateway that proxies communications with other internal servers and devices through SSH tunneling. Configuring Local Port Forwardingįigure 1 shows a simple example of local port forwarding. ![]() Local port forwarding allows you to make a connection with a remote server and then forward specified network traffic from your client to that server or beyond. You can configure SSH tunneling for local or remote port forwarding. For example, SSH tunneling can be useful for remotely connecting to your home devices. SSH tunneling is useful in specific situations, like where a dedicated VPN solution might be overkill. But as useful as SSH tunneling can be, it does have limitations and it will not provide nearly the number of features of a dedicated virtual private network (VPN) device. Then they can either connect to resources on that server using SSH tunneling or get directed to their destination on the private network. Users connect to this port, authenticate using a certificate, password, or other approved authentication method. For example, your organization might install a hardened SSH server on the internet that only listens on a single port running SSH. SSH implementations like OpenSSH can be centrally managed to provide authentication and encryption capabilities. Tunneling protocols over SSH is very quick and easy to set up and use. For example, some users might use SSH port forwarding to bypass your firewall if its rules block or filter HTTP and HTTPS but not block SSH. As a security operator, you will want to detect and manage SSH usage in a manner consistent with your security policy. Firewalls and other network tools generally will not be able to see inside these tunnels-they will only see the encrypted SSH (TCP port 22) traffic between the client and server (or gateway). The SSH local port forwarding feature allows you to create a tunnel between the client and server that encrypts all communications on a specified port between that client and server. ![]() Using SSH Port Forwarding to Securely Connect to Remote Systems You could also use SSH tunneling to create jump boxes and gateways that allow remote connections into your network without exposing additional network endpoints or ports. For example, you can use SSH tunneling to encrypt and forward web requests to a remote host without exposing that host's web service on the network. A lesser-known feature of SSH is the ability to forward additional, but different network traffic over this same communications channel. For example, it's common to use SSH to log into a Linux server to apply updates, install a new software package, or perform other administrative actions. ![]() Engineers and operators often use SSH to remotely administer their devices and hosts. The command-line tool secure shell (SSH) provides a secure communications channel between a client and a server.
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