SWMBO's iMac has stopped talking to the LAN.

No matter which router port I plug her Ethernet cable into, that port's activity light on the router stays off, and she has no LAN connection. My computer talks to the LAN when connected to any one of the four router ports, so the problem is probably not the router.

I temporarily connected the iMac to the router with a known-good Ethernet cable (very awkward cable routing because the temporary cable was too short for usable ergonomics) and the non-connect problem remained unchanged. The last time she used the computer (two nights ago) she had connectivity.

My knowledge of LAN connectivity extends about as far as plugging the Ethernet cables into the receptacles right side up. What should I look for to try and solve this problem?

tanstaafl.

Apple slipped up and sent out a security update that accidentally blacklisted the ethernet driver for a short period of time in several Macs.

Connect the iMac via WiFi and it will fix it's self after about a day. Or follow the more involved steps in this support article.

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

About three hours after connecting with WiFi the problem is solved, the "Incompatible Kernel Extension Configuration Data" now shows v3.28.2, the router blinkies are shining, and all is right with the world.

Thank you Tom!

But I have to wonder... why is there not a big outcry on the internet about this problem? Wouldn't there be millions of computers affected? Or do they roll these updates out in little batches and find and fix the surprises before they can affect very many people, and SWMBO was one of the "lucky" ones?

tanstaafl.

There was some coverage:

http://9to5mac.com/2016/02/28/apple-conf...res-how-to-fix/

https://www.reddit.com/r/apple/comments/47tfos/warning_software_update_03151913_breaks_ethernet/

http://www.techinsider.io/apple-confirms...e-update-2016-2

http://www.ubergizmo.com/2016/02/apple-fixes-mac-ethernet-port/

But yes, a surprisingly small amount of outrage, compared to normal. I suspect that the vast majority of Macs are using wifi rather than Ethernet nowadays, so of the subset of Mac users who were using machines hit by this only a fraction of them would have noticed.

More coverage is coming out today. The problem seemed to hit at the perfect quiet time for the press going into the weekend. At least this is actual Apple news, I'm sure we will be back to random rumors of how unreleased products have been renamed or how unreleased products lack ports pretty quickly.

And agreed on why it wasn't a big outrage event in the Mac community. OS X setup helps configure WiFi, many users probably have it set up even if they also use ethernet. Interestingly it did blacklist the Thunderbolt ethernet adapters too. Apple's support side probably had a number of people contact them. Warranty or no, people were likely advised of the support article above.

My home Mac Pro is on both ethernet and 802.11ac WiFi, so that it can take advantage of all the Continuity features. The brief usage I had on the computer this weekend did cause it to pull down the bad update, leading to it switching over to WiFi as default. Later it pulled the fix down over WiFi and ethernet returned.

One theory someone on Twitter had: It was an accidental release intended only after 10.11.4 ships. It's possible some sort of security vulnerability is sitting in the current driver. This page will have an update once 10.11.4 exits it's current beta phase: https://support.apple.com/en-us/HT201222