WAN emulator

This post talks about making a WAN emulator from a Raspberry Pi. As the Pi runs a derivative of the Debian Linux operating system which has native packet shaping features it was an ideal choice for making a WAN emulator. The aim was to connect the Pi between a client PC and the network and allow me to simulate things like packet delay or loss. I could then get the customer to repeat transaction on the client PC and we could observe/time the effect of different network characteristics. Not only a good tool for investigation but an ideal tool for demonstrating the effect of network latency for people considering data center moves or dismissive about complaints about poor performance for users in the “regions”

I had a RaspberryPI Model B but need a few things for the WAN emulation.

  • Additional Ethernet port – the Pi has only 1 ethernet port so I needed a Ethernet to USB device. A simple eBay purchase for a few quid
  • Screen – Again another ebay purchase for a 7 inch screen with separate PSU. The screen is a bit bulky compared to the rest of the kit and I have noticed recently that there are 5 inch screen that connect direct to the Pi with no PSU needed.
  • Keyboard – Another ebay purchase of a 7″ keyboard with MicroUSB and tablet case.
  • Finally I need a HDMI connector and a MicroUSB to USB converter

The kit is all connected together and can be seen in the picture below.

 

Next you have to create a bridge between the two Ethernet adapters. This is done with the follow commands, which I have in a .sh file and run once the Pi is booted. This turns the Pi into a transparent bridge between WAN and Client PC.
ifconfig eth0 0.0.0.0
ifconfig eth1 0.0.0.0
brctl addbr bridge0
brctl addif bridge0 eth0
brctl addif bridge0 eth1
ifconfig bridge0 up

Next you can use tc to inject delay and packet loss. For example to add a 50ms delay

tc qdisc add dev eth0 root netem delay 50ms

It has been a few months since I built this and I apologies if I have forgotten any steps around installation but I found a quick google solved any problems.

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