WAN Latency Simulation in Windows

I’m currently working on a project for a client that involves the implementation of Microsoft SQL Server Replication on some very heavily loaded databases. The implementation is to replace an outdated system that cannot keep up with the load and especially high-latency connections such as links from Europe to Asia. To make sure the new architecture will support the needs both load and latency testing need to be performed to make sure that we’re not swapping one bottleneck for another.

The last time I looked at this was a couple of years ago and I ended up with solutions either involving hardware WAN simulators, hacks within VMWare ESX or Linux-based systems. The various Windows implementations I found were particularly flakey.

There are limitations with my client that mean hardware or changes to the ESX host are not viable and as such they need to be done within Windows itself and ideally in a transparent way. My requirement was solely adding latency and applying it across the entire TCP/IP stack to make sure we’re not neglecting anything. I’ve seen plenty of solutions that can act as a proxy and intercept specific ports but I wanted a more blunt instrument and found a wonderful tool

Introducing Clumsy

Demo showing the various modes of operation within Clumsy

This is a fantastic free tool. It uses WinDivert to hook into the Windows networking stack and impact your packets real time. You can filter specific TCP/IP streams or apply it across the board. It also works with loopback connections (with a couple of limitations). There’s nothing extra to install and it “just works”. All you need is admin rights.

If anybody is looking for a really simple tool to simulate WAN latency on Windows then I highly recommend this tool.


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