It used to work; unfortunately, Apple removed ipfw from recent versions of OS X.<p>The new method uses dummynet and pf but isn&#x27;t reliable and I&#x27;ve never got it to work consistently, despite trying for hours and hours.<p>The only method that works reliably on recent versions of OS X is the free Network Link Conditioner. It is absolutely bulletproof.<p>Edited to add: Network Link Conditioner seems to use pf and dummynet under the hood; you can see the rules appear. But there&#x27;s an interaction with the nlcd daemon that I don&#x27;t understand yet. I want to do protocol-specific bandwidth throttling and I&#x27;ve not got that to work with nlcd interfering. But if you can live with throttling <i>all</i> traffic on the box, NLC works a treat.