Imac OS X El Capitan 10.11.6 - ethernet connection to modem not working

[fluffs]

New Modem can’t connect via ethernet cable - but can wireless - want to connect via ethernet

Checked cable good - iMac port ok - swapped modem port still no - used Dell laptop to connect via ethernet and wireless and all good - so assume somethings blocking me.
Restarted several times during all above processes, also re-started modem several times, and reset.

Read it could of been a software update that breaks the ethernet connection, but patch link no longer works.

http://swcdn.apple.com/content/downloads/47/55/031-52551/djk479pucjbs7r2ln9u3n0573nt31ifb45/AppleKextExcludeList_10_11.pkg

Apparently this was a common problem, with patch, but can’t find fix, please help.

Running a iMac 2011, OS X El Capitan 10.11.6 -
Please don’t suggest update - long story due to programs running

Here’s a link

Apple Security Update mistakenly disables Ethernet ports

Apple today made an error with a security update that could have a high IT support cost.As reported in MacRumors Forums,“Software update 031-51913”, designed...

grahamrpugh.com

 

[Fishrrman]

If you can't find "a software fix", I'm wondering if you could plug in a 3rd-party USB-to-ethernet adapter (many are available, they're cheap), and get a working ethernet connection that way?

Another option:
Download the latest posted el cap 10.11.6 "combo" update, which you can find here:

Download OS X El Capitan 10.11.6 Combo Update - Apple Support

The OS X El Capitan 10.11.6 Combo update improves the stability, compatibility and security of your Mac, and is recommended for all El Capitan users.

support.apple.com

Then, "apply it against" your existing software installation.
It should NOT "hurt anything", and it MIGHT fix the problem.
NO promises, but I would try that...

 

[fluffs]

Apparently can't do "combo" update for some reason.?
.

 

[chrfr]

Apparently can't do "combo" update for some reason.?
.
View attachment 898048

Once you've installed security updates, the operating system is too new to reinstall the Combo update.

 

[Fishrrman]

Yes, what chrfr said makes sense.

OP...

If you don't want to try the USB/ethernet alternative, seems like your only choices at this point are to
- go backward -- wipe the drive and re-install "up to the combo update" (if that's even possible), but then "go no further"
or
- go forward -- I'd suggest trying 10.12 "Low Sierra".

Do you have an EXTERNAL USB3 drive? Use that as your "test platform" for either of the above approaches.
That way, you can experiment without "touching" your existing internal drive.