If Apple hasn’t yet made the Ethernet network port on your Mac obsolete by not including it, as is the case with most Macs sold today, then it may have accidentally broke the port last week in an OS X kernel extension update. Many users complained about the issue online: they had randomly found their Macs no longer connecting to the Internet and their Ethernet port simply not working. Apple has now officially acknowledged the problem on its support pages. Luckily, the software problem isn’t permanent and the bug can, usually, be easily resolved.
Apple has already fixed the Ethernet software problem for users going forward. Here’s the fix if you were affected ..