It’s called NAT loopback!

Posted on June 14, 2013 in Εxperiences

I don’t consider myself an expert when it comes to networks, but my knowledge is above average. That said, I often find myself struggling with network problems that even the experts can’t answer. Apparently there are experts and… gurus! And personally the only guru I know is Google. So here’s my latest problem and what I’ve learned from it.

My Internet provider: OTE, gave me a ZTE W300 router which isn’t all that bad. It kinda misses a few features but it does the job, not to mention that it’s stable and locks to a decent ADSL speed. But users like me, most of the times aren’t happy with anything in its default state. So from day one I installed a Netgear modem/router with all the bells and whistles a geek can ask. I setup my firewall, my port forwardings etc. and everything seemed to work. At least for a few months. Netgear at first started acting strange with my LAN printer. There were times when all my computers could see the printer with no problems, but most of the times he was lost… as in lost in my local network. Besides that, I noticed that all the online games that I’ve tried suffer from latency issues, even though the rest of my Internet was pretty fast with zero problems.

Installing the ZTE modem/router solved the printing problems as well as the game latency issues. So it’s pretty obvious that something is wrong with my Netgear. But ZTE isn’t flawless either. I’m running a few services on my server that I want to be able to access them by using my external IP no matter if I’m home or if I’m using the Internet. The Netgear router seemed to handle this just fine by default. The ZTE though doesn’t allow a local LAN user to access a local service by using the external IP or a hostname service like Dyn.

After several hours of testing various suggestions from friends, I stumbled upon a “magic” forum post. Obviously there were others with the same problem but a real guru was able to understand the problem and solve the mystery. The ZTE W300 doesn’t support the feature NAT Loopback.

NAT Loopback allows you to access the external IP address from inside your home or office network. This is useful when you run a server inside your network. It allows you to use the same public IP address (and hence hostname) to access the server from both your home or office network as well as from the Internet.

That’s when I realised that I was looking for a solution to a missing problem. My ZTE doesn’t’ even support the feature that I thought was having a problem! And here I am writing this post for people that might come up to a similar problem. Of course I took my problem to a new series of searching, like how can I enable NAT loopback to a ZTE W300! And the funny thing is that I did find someone mentioning a telnet command that can enable this feature. But I wasn’t surprised when I found out that another problem was waiting for me.

Doing a telnet to my routers IP resulted in a username and password request. I believe I tried every single thing I found on the Internet regarding default password on ANY router brand! Nothing worked. And when I finally called OTE to tell them my problem, not only they didn’t know the telnet account for the router they provided me, they also said that there is no way to turn on NAT loopback on that device and that I should buy a newer one.

I really hope that no one ever runs into the above problem. But if you do and you actually figure out how to enable NAT loopback to the ZTE W300, I would love to know how. Even though I’ll probably be getting a new router that supports ALL my needs!

    • JP

      Some modems don’t support NAT loopback, therefore you cannot solve it. Probably your ZTE is one of them! I know for a fact that there are a “few” routers in the market that fully support NAT and they are sold by Cisco, which means that you’ll need above 100€. Anyways, in case you haven’t tried it set the modem on bridge mode, that way you’ll might solve your problem. Then you can put an old computer after the router, install Linux and NAT over that.

      • Thanks for your suggestion JP. I’ll keep it in mind for future reference. For now, a new firmware update fixed all my problems with the Netgear modem/router that I had. So until the Netgear dies, I’ll try not to fiddle too much with my network.

    • Federico

      Hi!

      I, as you, had the same problem, came upon you blog, and almost cried for a while, but wasn’t about to give up yet, so kept trying, and the result was that, well, the ZTE W300 does have NAT LOOPBACK.

      The trick is to, as you say, be able to telnet. To my luck, I had the router admin password that my ISP uses (is the same you use to log in to the web admin interface). The full list of commands is:

      1- $: telnet x.x.x.x
      2- (INPUT PASSWORD
      3- ZTE > ip nat loopback on
      4- ZTE > exit

      Done, loopback works.

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