2012 Mac Mini keeps dropping ethernet connection

[fhall1]

2012 Mac Mini i7, (specs in sig). Running OS X 10.10.5. I've owned this since it was released in 2012 and have had no issues with it until a couple weeks ago. There have been no OS updates or other s/w hardware additions that I could attribute to this issue.

I've noticed that a few times a day, a notification will pop up that my wired ethernet connection went down, then back up. Originally it happened so sporadically I just ignored it. But yesterday it happened about 50 times in a row, up down, up down, up down. Usually when it finally would reconnect, the interface would be at 100baseT instead of 1000baseT. Syspref is set to automatically configure.

My home network hasn't changed during this time either. My cable modem (Motorola SB6141) feeds a Cisco (Linksys) router, that feeds an Apple Airport Extreme (latest gen) and another router (I run two separate subnets, one for business, one for home). The AE feeds an 8 port switch that my Mac Mini is plugged into. I've reset the cable modem, the Linksys, the AE, and tried different ports on the switch....note that no other machines on the network exhibit any strange network anomalies.

I did a safe boot yesterday and that seemed to help for a while, but I noticed just now the switch lights for the MacMini port are orange instead of green, indicating 100baseT and sure enough it's verified by the syspref config.

Below is console output related to en0 for today:

2/20/16 8:19:45.000 AM kernel[0]: AppleBCM5701Ethernet [en0]: Link down (womp disabled, proxy idle)
2/20/16 8:19:45.689 AM configd[51]: network changed: v4(utun0:10.105.1.6, en0-:192.168.11.83) DNS! Proxy- SMB-
2/20/16 8:19:49.000 AM kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug [796d,0301,0de1,0300,cde1,3800]
2/20/16 8:19:51.173 AM configd[51]: network changed: v4(en0+:192.168.11.83, utun0) DNS! Proxy+ SMB+
2/20/16 8:29:49.000 AM kernel[0]: AppleBCM5701Ethernet [en0]: Link down (womp disabled, proxy idle)
2/20/16 8:29:49.279 AM configd[51]: network changed: v4(utun0:10.105.1.6, en0-:192.168.11.83) DNS! Proxy- SMB-
2/20/16 8:29:53.000 AM kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug [796d,0301,0de1,0300,cde1,3800]
2/20/16 8:29:55.637 AM configd[51]: network changed: v4(en0+:192.168.11.83, utun0) DNS! Proxy+ SMB+
2/20/16 9:40:19.000 AM kernel[0]: AppleBCM5701Ethernet [en0]: Link down (womp disabled, proxy idle)
2/20/16 9:40:19.961 AM configd[51]: network changed: v4(utun0:10.105.1.6, en0-:192.168.11.83) DNS! Proxy- SMB-
2/20/16 9:40:24.000 AM kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug [796d,0301,0de1,0300,cde1,3800]
2/20/16 9:40:26.216 AM configd[51]: network changed: v4(en0+:192.168.11.83, utun0) DNS! Proxy+ SMB+
2/20/16 9:41:44.000 AM kernel[0]: AppleBCM5701Ethernet [en0]: Link down (womp disabled, proxy idle)
2/20/16 9:41:44.327 AM configd[51]: network changed: v4(utun0:10.105.1.6, en0-:192.168.11.83) DNS! Proxy- SMB-
2/20/16 9:41:47.000 AM kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 1-Gigabit, Full-duplex, Symmetric flow-control, Debug [7949,0021,0de1,0300,0000,0000]
2/20/16 9:41:48.000 AM kernel[0]: AppleBCM5701Ethernet [en0]: Link down (womp disabled, proxy idle)
2/20/16 9:42:01.000 AM kernel[0]: Ethernet [AppleBCM5701Ethernet]: Link up on en0, 100-Megabit, Full-duplex, Symmetric flow-control, Debug [796d,0301,0de1,0300,4de1,0000]
2/20/16 9:42:03.324 AM configd[51]: network changed: v4(en0+:192.168.11.83, utun0) DNS! Proxy+ SMB+

At 9:42 the link changed from 1-Gigabit to 100-Megabit, but I don't see why. Any ideas on what's happening from the console log? Logic board issue? Other?

 

[DJLC]

Have you tried a different Ethernet cable?

Since it's sporadic and only increased recently, I'd tend to look toward a worn or poorly terminated cable. Failing that, I'd start to look at OS X or LoBo issues.

 

[fhall1]

Easy enough to try a different cable. I'll report back.

 

[glutenenvy]

Try the cable and hub/switch first. It is easier than monkeying with software settings. Get a newer hub and place it between the computer and the existing cable. Use a new cable between the newly placed hub and computer. This way you can determine if the central hub or cabling is to blame. Sometimes the fix is just to leave the testing hub in place as the lines up to your computer may have become underpowered through decay or breakdown. I did have an intel server nic where all the welds on the cat connector broke off at the same time. Your mini could be breaking in a similar manor but it is still pretty new for a freak occurrence like that to happen. Don't forget to also try swapping ports at the central hub.

 

[glenthompson]

Cable testers are cheap enough that you might want to have one handy. Very helpful for diagnosing cable problems.

 

[satcomer]

I'm concerned about the proxy changing on it's own. Scan it with the free Malwarebytes for Mac to see if finds anything.

 

[fhall1]

Malwarebytes found nothing. What I did was run a new cable from the switch to my Mac Mini. Hopefully not jinxing it, but it's been a week with no network drops or speed changes. It'll be great if the fix was that easy! Thanks all.

 

[LiveM]

Apple broke the ethernet port with a recent update. Have you checked the fix? It seems this might cause intermitent operation besides total inoperability.

https://support.apple.com/en-us/HT6672

 

[fhall1]

The Apple update was 2 days ago....my issue has been going on for a couple weeks. So far looks like it was a cable that "went bad"