On 26 February 2016, Apple pushed an update to the Incompatible Kernel Extension which came with a bug blocking the loading of the kernel extension responsible for implementing the Ethernet port on many Macs. Its effect was to completely disable and vanish that Ethernet port when an affected Mac was next started up. Apple didn’t push a fixed update until two days later, and neither apology nor explanation was ever provided.
Diagnosing that and other network problems isn’t easy. We tend to try a few things at random, hoping that we can guess right quickly. Although this can solve some problems simply, when they prove more obscure we often don’t know what to do next. Using a more systematic approach is then essential, and the subject of this article.
Key tools for working with network problems are the Network and Sharing panes where services are configured, and the Wireless Diagnostics app. As I’ve recently explained its use in detail, I won’t repeat that here. One important collection of tools, Network Utility, has now been removed from macOS Monterey; the best third-party replacement for that is Bryan Christianson’s superb and superior WhatRoute, which I’ll use here.
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