Real World Example: Setting up a dynamic IP for remote ssh sessions – for free!

Yet another Real World Example (RWE)! I know it has been a while since I have posted one of these, but it is better late than never, right?

The situation: An undisclosed party needed a way to log into their Linux computer from anywhere. Particularly from their home computer, or their cell phone while on the go. This is pretty handy, as an admin can log in, restart/start/stop services, and check on status without driving back to the office. They also didn’t want to spend any money for services, or purchase any new equipment, it just wasn’t in their budget.

The Solution:

The first thing that we had to discuss was what kind of connection they needed. In this case it was an SSH session, which is great as far as bandwidth and setup. However, this scenario would work just as well for Xrdp, vnc, ftp, etc., it just helps that in this case it was a “simple” fix that would be quick to set up.

The second thing that we needed was a way to establish the address of the computer in question. We will refer to the computer that they wish to connect to as the server, and we will refer to the gadget that they are using to connect as their cell phone or home computer. We needed a way to tell the cell phone the ip number of their remote server. Since they do not have a staic WAN IP address assigned to their router, they do not have a hard and fast “set” WAN IP address that does not change, instead they have the dynamically assigned IP address that gets changed potentially every time they connect to the internet, or every DHCP renewal to their router, etc.

The best answer to this problem would be to pay for a static IP address and assosiated Dynamic Name Services (DNS) so that you have a hostname that you type into your home computer or cell phone which always leads to your server. Ths service actually cost money, and hense would be outside of their budget.

So how did we solve this issue? Well, enter No-IP for free ( http://www.noip.com/free ), which is an internet based company that has a few very handy tools to do just that. As we will see from the following, setup was really easy, and FREE. By free, they mean, FREE. Which is pretty nice these days. Now, they do have upgrade options which are not free, but the basic package is completely free.

The first thing that we had to do was register an account for them. Once registered, we added a “hostname” for them. They have many to choose from, such as “myhostname.ddydns.org” and “myhostname.zapto.net”. We will not discuss their actual choice to protect the innocent, but for this example I will continue with myhostname.zapto.net.

Second, we set up the computer with their DUC (dynamic updater client) which we downloaded from their website. It comes as a tar file, which we unzipped, and then we ran make install to put the files where they needed to be. It was really pretty simple and had a few straitforward questions in the config file, as well as instructions on how to start and stop the service, and how often it should update.

This DUC tool is what makes it all work. The DUC tool finds out what your router’s dynamic (changing) WAN IP address is at any given moment, and sends a packet to the No-IP server to tell it your present dynamic IP address. So when you connect to myhostname.zapto.net, it is actually asking No-IP’s server what the current WAN IP address is for your server. Pretty slick trick actually.

Once that was done, we of course needed to do the basics, such as installing the SSH server. In this case we chose to:

$ sudo apt-get install openssh-server

Which istalled OpenSSH Server. Now I don’t want to get too deep into the details of their setup, for security purposes, but I will cover the basics here. I highly recommend that you choose an arbitrary port other than 22 for your SSH connections, to help trick those who do wrong from attempting the connection. It may even be wise to pick a port that is used for something else. For the remainder of this explanation, though, I will explain what we did using the standard SSH port 22.

For security reasons, you should also not allow root logins, but rather use a special user who can then sudo or switch user to root with a password. This double door password feature will likely save your bacon if someone gets in. You should also use an obscure username, not something like admin, ssh, maintenance, or server. Finally, you should have a really complicated password, one that is as complicated as you can remember. In this case, we actually had to change their password to something a little tougher, because theirs was too short and a dictionary word, which is bad. Also be sure to properly set up your firewall, which is something we will not talk about here.

The next step on the bucket list was to configure the router. Which has several smaller steps, but which were easy to manage locally. Their server already had a static IP on the Local Area Network, but if you are setting this up for yourself, say at home, be sure to give your server a local static IP address from your home router. This is usually done based on the server’s mac address. In this case, consider it 192.168.2.41.

After all that, we were down to the final step, which is to configure the router for port forwarding. Most routers have a web gui that is fairly intuitive, and you will need a guide for your router to complete this step. In this case, we assigned anything coming in on port 22 to be forwarded to the local IP address of the server computer, or 192.168.2.41:22. Note that the :22 means to send it to port 22 of the local computer.

Now the setup was done and it was time to test it. Which I did from my cell phone. Having an Android phone running SlimLP (5.1.1) I used an app called JuiceSSH. It is a really great app that is well constructed, looks snazzy, and works flawlessly. It also allows screen rotation, and even has special keys such as tab and ctrl. So in the app, I chose to set up a new connection to myhostname.zapto.net, port 22, with the appropriate username and credentials. Once I clicked connect, I was greeted by some scrolling information about echanging keys, passwords, etc., and eventually the remote server’s command prompt. Success!

All told, that was a pretty simple fix for a complex problem! Not to mention it was completely free. One down side to the free option, however, is the need to renew your free hostname every 30 days. That’s a pretty easy trade off for the free service though. Also, the free package only includes 3 dynamic addresses. So if you want to do this for a large business, you are better off with a paid package.

Linux – Keep it simple.

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