WANatronic 10001: An extremely simple WAN emulator

14Jul/110

WANatronic 10001: An extremely simple WAN emulator

This article discusses a new free, WAN emulator to rival others like WANem.

Features of the WANatronic 10001 virtual appliance (you can run on VMware Workstation, and probably ESX and Fusion as well):

Traffic sent directly to WANatronic 10001 is sent right back to whatever host it originated from. If you ping WANatronic 10001 you’re actually pinging yourself. Same with SSH, etc.
Packaged as a VM needing 32MB and a download size of about 170MB, which unfortunately is small as far as virtual appliances go.
There are 4 things you can configure. If you’re lazy and don’t configure anything, WANatronic 10001 will still work.
That’s pronounced WAN-a-tron-ic ten-thousand-one in case you were wondering. Just try to forget that name. See? You can’t do it.

Using WANatronic 10001

Possibly the most interesting thing, and the thing I think I’ll use it most for, is simulating slow links on a single host. In this case there is nothing you need to do on your computer. In the screenshot above my WANatronic is at 10.24.0.13. Any traffic I send to that IP is sent right back to me. So if I have two processes on my host that I want talking slowly, let’s say one is on port 8000 and one is on port 9000, all I do is tell the first application that its peer is on 10.24.0.13:9000 and tell the second one its peer is on 10.24.0.13:8000. Done.

WANatronic can also function as a router-on-a-stick, all you need to do is route traffic through WANatronic. For example Google’s free DNS is located at 8.8.8.8. If you want to simulate being on a slow network between here and there run:

ip route add 8.8.8.8 via 10.24.0.13

Your IP address will be different from mine, check the console to see what it is. You may need to adjust that command based on your OS. With that set up, ping 8.8.8.8 to see the effect of latency and packet loss.

Last but not least, configuration is via the console since there is no way to remotely connect to WANatronic. Changes are automatically saved and applied.

Technical Mumbo Jumbo

WANatronic uses Ubuntu 8.04 JEOS as a base. I used this older distro to cut down on the size of the virtual appliance, which unfortunately is still huge. For the most part WANatronic is a very basic use of the iptables and tc utilities. The WANatronic source code is hosted on GitHub.

There is one exception that required a little bit of science. I really wanted any traffic sent to WANatronic to be NATted directly back to me. Without this I would need to use multiple network interfaces which I wanted to avoid. As far as I can tell there’s no way to do that with iptables, so I made a custom version of the iptables NETMAP target that would replace the packet’s destination address with its source address in PREROUTING. After that the packet is NATted so it appears to originate from WANatronic. This is the magic that lets you talk to yourself on what appears to be a very crappy link. Perfect for a demo that needs to reside completely on a single laptop.