How to access SSH when Pi is connected to the internet through PC?

Question

I have my Raspberry Pi (Model B Rev. 2 UK) connected to my PC through an Ethernet cable, which provides the Pi with an internet connection and allows me to SSH into it. It took me a few hours to get this working (pinging raspberrypi in the Windows console could not find the hostname and Pi finding software did not work, static IPs of 192.168.1.2 allowed me to connect if I set my LAN to 192.168.1.1 but the network did not work, I have no HDMI screen so I needed to edit the SD Card files in a Linux VM, etc.) and now I can finally connect and SSH.

My computer to which the Pi is connected is connected to the internet via WiFi and has the IP 192.168.0.5 on the Wifi card and 192.168.137.1 on the Ethernet card.

The Pi can access the network, but I would like to access the Pi outside of my house. My port 22 is portforwarded and my Connection sharing of my Wifi adapter has an SSH entry added.

Edit: here is my /etc/network/interfaces file:

iface eth0 inet static

    address 192.168.137.2
    netmask 255.255.255.0
    gateway 192.168.137.1

Answer 1

Here's a diagram of your network:

Router <---> PC <---> Pi

First off, your Pi is connected to your computer, which is connected to your router. I'm not sure why, but here's one way it can be done:

1. Make sure your router's port forward is pointed to your PC (192.168.0.5) and not the Pi (192.168.137.2). This is because packets cannot magically skip a router when jumping between subnets. Therefore, your PC has to act as a router. I assume you have a subnet mask of 255.255.255.0.

2. Now that your primary router knows where to forward traffic, your PC should now be receiving packets on port 22. The problem is that your PC doesn't know what to do with them, so treating your PC as a router, you somehow have to "port forward" 192.168.137.2 port 22 on your PC.

If you're on Linux, it should be a breeze. If you're on Windows, you somehow need to find an equivalent of these Linux commands:

iptables -t nat -A PREROUTING -p tcp -i wlan0 --dport 22 -j DNAT --to-destination 192.168.137.2:22
iptables -A FORWARD -p tcp -d 192.168.137.2 --dport 22 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT

These basically mean if traffic is coming from wlan0 (wifi) port 22 and is heading to 192.168.137.2:22, accept it, NAT it, then forward it.

I haven't tried bridging the two connections (WiFi and Ethernet) right away. If that's the case, simply point the port forward to the Pi directly on your main router. (or at least that's how I think Windows networking works.)

Visualizing the network first really helps with coming up with a solution, hence the diagram.