Network Link Conditioner – Simulating a BAD Network

Last week, I wrote an article about Building a BAD Network with Dummynet. While the goal of that article was to document a flexible “drop-in” solution that would create performance issues on a given Ethernet segment, this week’s article will introduce a simple way to simulate a poor network connection for applications on a Mac. The product that I want to introduce is called Network Link Conditioner and is available for OSX.

Obtaining and Installing Network Link Conditioner

To find this product takes a little bit of digging. It is located as an “additional tool” in the Xcode section of the Apple development site. This can be found by going to the following URL and choosing the applicable link.

Download Network Link Conditioner

After choosing the download link, Apple will require a login. While an account is required, it does not have to be a paid account. Network Link Conditioner is part of the “Hardware and IO Tools” package and is considered a developer tool. The current package is dated October 2013.

Using Network Link Conditioner

After downloading and installing, I recommend doing a reboot. Although it might not be required, my installation didn’t seem to work correctly at first. After installing, there is an option in System Preferences for Network Link Conditioner. Opening this reveals a Window similar to the following.

Network Link Conditioner

Network Link Conditioner may be toggled on and off simply with the switch on the left. Different network profiles can be selected by using the drop down box on the right. Changes take effect immediately.

Network Link Conditioner From Good to BAD

Advanced Profile Settings

To add to the flexibility, developers and users can create their own network profiles by choosing “Manage Profiles”. The parameters that may be tweaked are shown in the right two thirds of the image below.

Network Link Conditioner Profile Settings


Although Apple’s Network Link Conditioner is not as flexible as the solution outlined in last week’s article, it is a very effective. More importantly it is easy to use and implement. Network Link Conditioner can be a very effective solution for testing application performance with varying network conditions in a Mac environment.

This article was meant to introduce users to the Apple Network Link Conditioner utility. If you are a current user and have use cases or comments, please share them below. I love hearing from PacketU readers and fellow network professionals.

About Paul Stewart, CCIE 26009 (Security)

Paul is a Network and Security Engineer, Trainer and Blogger who enjoys understanding how things really work. With over 15 years of experience in the technology industry, Paul has helped many organizations build, maintain and secure their networks and systems.
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