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SSH: My Favorite Tool

Explore the power and versatility of SSH, the essential tool for secure remote access.

Lock, Key, and Command: The Magic of Secure Shell

Secure Shell (SSH) is a cryptographic network protocol used for secure data communication, remote shell services, and command execution. It's an indispensable tool for system administrators, developers, and anyone who needs secure remote access to servers and other networked devices. With SSH, you can manage your servers from anywhere in the world, transfer files securely, and even tunnel traffic through encrypted channels, all with robust authentication mechanisms and encryption to ensure your data remains private and protected. SSH is my favorite tool because it provides a secure, efficient, and versatile way to manage and interact with remote systems, making it an essential part of any IT professional's toolkit.

Using socat for Port Exposure vs Port Forwarding

socat is commonly used to make services reachable when they are bound only to localhost.

Option 1 – Expose a local-only service to the entire machine

sudo socat TCP-LISTEN:8001,fork,bind=0.0.0.0 TCP:127.0.0.1:8000
What it does
  • Listens on all network interfaces (0.0.0.0:8001)
  • Forwards traffic to a service bound to localhost (127.0.0.1:8000)
  • Requires sudo because it exposes the service system-wide
When to use
  • The application only listens on 127.0.0.1
  • You want the service accessible from other machines on the network
  • Very common for dev tools, dashboards, scoreboards, internal web apps

This is the most commonly used pattern, because many services bind to localhost by default and just need to be exposed.

Option 2 – Redirect traffic to another host or IP

socat -dd tcp4-listen:8001,fork,reuseaddr tcp4:IP:8000
What it does
  • Listens on IPv4 only
  • Forwards traffic to another IP or host
  • -dd enables verbose debug output
  • reuseaddr allows fast restarts
When to use
  • Acting as a simple TCP proxy
  • Forwarding traffic to a remote machine
  • Debugging or tracing TCP connections

This is less common for local services, and more useful when relaying traffic between hosts.

In practice:
Most people use the first command because it exposes a local-only service to the whole machine, which is the typical need.

Most commonly used methods of connections (click to expand)

  • Copy Paste - SSH -X option enables X11 forwarding, allowing you to run graphical applications on the remote server and have their display output on your local machine.

    ssh macpro -X
    Needs to set X11Forwarding yes

  • SSH -J option specifies a jump host, allowing you to connect to a remote server through an intermediate server.

    ssh -J first-user@IP 2-user@192.168.100.246

  • Local Port Forwarding ssh -L



    Access to resources that I can't access, like internet Database, RDP

                
            	Tambien funciona con socat
socat -dd tcp4-listen:8080,fork,reuseaddr tcp4:IP:8080

            		**** ssh configuration on XPS server needs to have: ***
            	****  AllowTcpForwarding yes  ****


curl localhost:8888
curl: (7) Failed to connect to localhost port 8888 after 0 ms: Couldn't connect to server 
        
ssh -L 8888:192.168.80.246:8080 xps
        
curl localhost:8888
Internal server web
flag:as1ds5a6d1a65

  • Remote Port Forwarding ssh -R

    I want my own server be access to anyone

                
            	**** ssh configuration on public server needs to have: ***
            	**** GatewayPorts yes ***


❯ ip r
default via 192.168.88.1 dev eth0 
192.168.88.0/24 dev eth0 proto kernel scope link src 192.168.88.68 
❯ curl http://192.168.88.93:8888/
curl: (7) Failed to connect to 192.168.88.93 port 8888 after 0 ms: Couldn't connect to server 

#This is execute on XPS        
ssh -R 8888:192.168.80.246:8080 public@192.168.88.93 
        
curl http://192.168.88.93:8888/
Internal server web
flag2:E2lsa3aasd5A

  • SSH -D 1080 proxy

    Setting up foxyproxy

                
**** ssh configuration on public server needs to have: ***
            	**** AllowTcpForwarding yes ***

             
        
ssh -D 1080 user@192.168.88.13 -p 2246