This all started years ago when I was wondering why my laptop could see my Wemos D1 mini OTA while my wired desktop could not. I put it down to general quirk from having 2 versions of python inside as well as close to a decade of computer use without a reformat.
In February this year I finally made the upgrade from an old i5 750 (first gen) system to an Intel 8700K which meant a brand new install.
Long story short, as I was (re)setting up my desktop, I happened to connect to WiFi instead of the wired network. I noticed straight up that my Arduino IDE could see my D1 minis.
Cut to a few days later, when I was back on wired, I noticed that it was missing again. Reconnecting to the WiFi confirmed my theory that mDNS packets were not traversing the gap between the WiFi and the wires.
After a long time spent ruling out my router as the cause, I finally came to the realisation that my network switches were to blame.
After a long time searching and playing with IGMP snooping options (they don’t need to be on for this to work), I happened to come across a self answered question saying the the Anti DoS feature of TP-Link routers blocks mDNS, specifically, the Blat Attack subfeature.
I turned it off, and I started receiving packets again.
I did also need to explicitly allow UDP packets on port 5353 on my computer’s firewall too though.