Why is my Mac unable to connect to network

I was debugging some iOS apps with Charles Proxy and Charles froze on my Mac. I assume this was symptom of general network problem, so I rebooted my Mac and confirmed that it wasn’t able to connect to any web sites via web browsers or any apps.

The macOS network utilities (in /System/Library/CoreServices/Applications) worked fine, but command line apps like traceroute fail with no useful diagnostics or error messages. Neither WiFi nor wired connection work, though other devices on the network were fine. I rebooted all my network hardware, checked for firmware updates, ran Mac hardware diagnostics (by rebooting while holding down the d key), etc., and the problem persists with no promising leads. The only glimmer of hope is that when I use tethered connection via my iPhone, that works (!).

What is going on?