Skip to content

Dirt Cheap Oracle step #5(a) of 6: Port Forwarding & DDNS

September 24, 2007

[Previous]

Disclaimer: don’t blame me if you follow any of the instructions here and get yourself into a right mess – think of me as a helpful but aloof guide who occasionally gets his words mixed up :)

I can access Apex from the Linux box, but not from my WinXP machine across the network. This is because the firewall in Linux by default blocks most ports. I’ve got Apex (using EPG) listening on port 8080, and Apache web server (for the static web pages and images) listening on port 8000, so I open up those two ports (System menu -> Administration -> Security Level & Firewall).

The router, by default, assigns IP addresses dynamically via DHCP to each device that connects to it; in order that I don’t have to keep logging into the router to see what today’s IP address is, I need to tell the router to reserve an IP address for the Linux box. To do that I log into the router’s administration page (for mine it’s http://10.1.1.1), and examine the DHCP settings page. There I find that two devices are connected, each with a unique MAC address, and with the IP address currently assigned to them. One is the WinXP machine, the other is the Linux box. I happen to know which one is which, but I suppose if I didn’t know I could have just disconnected one of them and seen which one disappeared from the router. Anyway, I copy the MAC address and tell the router to assign it a static IP address (in my case, 10.1.1.3) (a word of advice: on some routers you have to also change the settings that specify the range of dynamic IP addresses that can be assigned by DHCP, so that they don’t conflict with the static IP addresses; in my case, my router does not work that way).

By the way, if my explanation of this doesn’t help you, just google “static IP address” – you’ll find heaps of guides around – keep reading, and it’ll all make sense…

Now I can access it from WinXP via http://10.1.1.3. For convenience I add a line like the following to C:\windows\system32\drivers\etc\hosts:

10.1.1.3        linuxpc        linuxpc

This means I can access it via http://linuxpc, at least from WinXP. The equivalent file on linux, used in exactly the same way, is /etc/hosts [Wikipedia: Hosts file].

What I want now is for friends and family to get to it from the outside. For security reasons there’s a number of things blocking that access which I need to take care of. Also, I want the URL that I give out to be relatively simple; a longish URL with strange numbers and characters can be intimidating and easy to get wrong. Also, at least one of my friends works at a place that seems to block different ports (e.g. 8000). So I want them to get in on port 80, which is the default for HTTP and doesn’t need to be specified in their browser.

At the moment the router ignores mosts requests from the outside world; it only exists to serve the little network connected locally to it and couldn’t care less about my friends and family. I need to make it just a little more friendly. First thing, I need to get a port mapped. In my router admin I navigate to the Port Forwarding (called “Virtual Server” on my router; on your router it might appear in “Network Address Translation (NAT/NAPT/PAT)” or “DMZ host”) section, and select the LAN IP I wish to map the port to (in my case, 10.1.1.3). This router gives me a whole lot of preset ports for various games and applications, but I want to do something different, so I select “User” and click “Add”. Here is where I can create a Rule for mapping ports. I want the router to accept TCP traffic on port 80 (the default for web stuff) but send it to port 8000 on the Linux box. So I give it a name (e.g. something imaginative like “Port80to8000″), select TCP for the Protocol, put in 80 for both Port Start and Port End, and pop in 8000 for the Port Map. I don’t need a range so Port Map End stays blank, and click Apply. Now, I just Add my new rule (Port80to8000) to the list of rules for 10.1.1.3, click Apply, and reboot the router. Now, traffic coming in from the outside on port 80 should be sent to port 8000 on the Linux box.

We’re not out of the woods yet, though, there’s a few more things blocking external access. Firstly, iiNet by default block any incoming traffic on port 80, as well as a few other ports, which is good from a security point of view, but doesn’t help me much, so I go into my account management page and switch this option off.

(Once that’s all done, I can test that external access to the port is working, by logging into the machine I want to test, and plugging 80 into this online tool: CanYouSeeMe.org – Open Port Check Tool.)

Finally, and this is the biggy, to get to my site from the outside, people need a URL; or at least, an IP address they can use (that won’t change from day to day). Now, I don’t have a domain name, nor do I have a static IP address – all I get is a dynamic (i.e. can change without notice) IP address assigned by iiNet. I could upgrade to a business broadband account with a static IP address along with a nice domain name, but I want to do this on the cheap, so I don’t.

Instead, I use DDNS (Dynamic DNS). I learned about this from an excellent article by Nathan Taylor in PC User magazine (May 2007). There’s a few sites out there that do this, the one I use is www.no-ip.com which provides a basic service for free. I sign up, get a domain name of my own (I won’t tell you what it is but it looks like mycomputer.no-ip.info), and plug in the settings into the DDNS page on my router.

The way this works is: whenever someone types in my domain name (e.g. http://mycomputer.no-ip.info) into their web browser, the request goes to no-ip.com. Their computer looks up their database for the current IP address for “mycomputer.no-ip.info”, and then forwards the request on to it. This process is pretty much seamless and without any overhead that I’ve noticed. Whenever iiNet change my IP address, my router sends a message back to no-ip.com with the new IP address and their database is updated so that future requests are passed on correctly.

If your router doesn’t support DDNS, don’t worry – you can get software that will run on a computer on your network, and it will do the same job – whenever the IP address changes, it will notify no-ip.com of the change.

After all that fun, I tried to test it from my WinXP box, but I just couldn’t get it to work. As it turns out, you just can’t access the local network using the external address from within that network – apart from using www.canyouseeme.org to check the port, you have to test your web site from outside your network. So I used my “phone a friend” lifeline and got him to try it out.

You guessed it, it worked first time. Ha! Well,… if I said that I’d be lying. It didn’t work first time, the actual process of working all of the above out was a little bit more bumpy than I’ve made out; but in the end it was all working, and I learned a great deal in the process.

There’s one more thing (oh no, I hear you moan…). You’ll notice I’ve only mapped port 80 to port 8000, which is the Apache web server, and not port 8080, which is Apex. That’s the subject of tomorrow’s post, so stay tuned!

[Next]

About these ads
Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 201 other followers

%d bloggers like this: