Frequent Ethernet Disconnects, Probable Cause



Reference close thread, Frequent (Ethernet) Disconnects

Recap from 2019: Late 2013 Mac Pro, frequent IP disconnects under Systems Sierra and Mojave. All Ethernet, NO Wireless involved.

Probable cause found.

BLUF: Brother 6545DW print driver software randomly forced the Mac to disconnect from the LAN, even with printer disconnected.

Much time has passed. Today my main Mac is Studio & System Monterey, and all is well. I think I finally found the likely cause of the frequent disconnects I had with my 2013 Mac Pro under System Sierra and Mojave.

I have a 2012 Mac Mini on the Lan, in a closet for doing some NAS work from time to time. Mac Mini (System Sierra) worked flawlessly for years with no LAN problems ever.

Mac Mini has no keyboard, no mouse, no monitor; I access it via Screen Sharing.

I had a need to print from the Mac Mini to an Ethernet connected Brother 6545DW printer. The brother print driver installer for System Sierra has to identify the printer on the LAN as part of the install procedure. It failed to ID the printer, and kept trying over and over. All the while the Mac mini was continuously disconnecting and reconnecting from the LAN every minute, over and over. I couldn't ping it until it came back up within Screen Sharing.

The Brother printer installer was causing LAN disconnects of the Mac Mini. Only fix was to use App Delete and remove all reminents of Brother software from the Mac Mini and all is well again.

It's the Brother Printer Mac software, not the printer, 'cause when I unplug the Cat5E from the printer, the problem persists. The brother software was literally taking full control of the LAN connect, forcing the Mac to disconnect intermittantly.

Fortunately, today, the Mac Studio, M1 chip, and System Monterey is robust enough to stay connected even if the Brother printer driver attempts to interfere.

It is unlikely or impossible that the 2012 System Sierra Mac Mini will ever be compatible with the Brother 6545DW printer. No big deal for me, as I can make PDF on the Mac Mini and pass it to the Mac Studio for printing. I plan to share this info with the Brother Corporation.

Why don't I just do it all on the Mac Studio? I'm using an "abandon-ware" application on the Mac Mini that's incompatible with higher systems.

Lesson Learned: Be suspicious of other applications that use the LAN.