Frequent (Ethernet) Disconnects

Internet connection goes offline frequently, and this is not about wifi. :)

Here's the setup:
Mac Pro (the Late 2013)
System Sierra 10.12.6
Firefox 62.0.b11
Static IP
Ethernet (not wireless)
Pace Uverse Modem with wifi always OFF.
Downstream ASUS router for Apple TV and other IOT things.

The Situation and Problem:

--Mac Pro only, other stuff on network is normal.
--Internet connection drops random about 6-10 times per hour
--Apple Network Diagnostics Control Panel (found on System Sierra and below)
- - Ethernet Green
- - Network Settings Green
- - ISP, Internet, and Server becomes either yellow or red, and the Mac won't ping out.
-- Connection will not return until I do something.

My Mac Pro setup:

Static IP is primary, although I tried DHCP.
Lan cables are tested and ok.
Nearby (Ethernet) windoze box is always up. (Same router)

Steps needed to get back online:

What I have to do, about every 10-15 minutes.
--Reboot or Physically disconnect ethernet from Mac, wait 10 minutes, reconnect, status returns to normal.
-- Network settings, manual.
Switch off (unplug) Ethernet
Change 4th octet AND DNS to something else
then switch ON Ethernet
I have to do this about 3-4 times trying various DNS's and static IPs. IP never comes back on the first try.

Network Radar tells me that my static IP choices are not in collision with something else.

Sometimes I change it to DHCP but results are usually fail.

Then I tried wireless, and wireless usually holds up a few minutes longer than ethernet, before the inevitable ISP, Internet and Server control panel indicators become yellow or red and I cannot ping out.

Changing the Cat port on the Mac made no difference.

Trying and changing DNS's

I've tried over 15 DNS's, including the AT&T DNSs and none are any better than each other, It's the changing of the DNS several times, that usually brings the Mac to all green for a while.
The always-up windoze box uses or Making these DNSs primary on the Mac fails to solve the frequent internet failures. I have a long list of DNS's that I've tried, none better than the other.

Rebooting the Pace Uverse modem will bring status back for a while, but its no better than changing the Network DNS settings. Nothing's wrong with the Pace router 'cause all other things on the LAN remain full up internet.

Running all the Onyx cleaning functions, especially the Onyx internet tab, made no difference. SMC and Pram reset bootups made no difference.

In the end, I get about 10 minutes of internet followed by 5 minutes of DNS and 4th octet changes needed to restore IP. 10-20 minutes later, I have to repeat the process to get back online.

Searches for the problem within the Apple website return problems and solutions for wifi only, with nothing useful about frequent Ethernet involved dropouts.

There has got to be something painfully obvious that I overlooked.
Any advice will be most appreciated.


In Geostationary Orbit
You need to first clean out massive Internet caches because it will give you the option to find where these old plugins reside! So use the mostly free YASU (Yet Author System Utility). It will show if and older plugin is causing the problem. The program doesn’t delete anything, it just points to the actual folder location to manually delete! Just let the program reboot your Mac if you delete old program plugins!
Hi, Have you tried checking if the problem lies on your network or computer? Use another computer or other devices that can connect to the same Internet connection. If all these devices on your network encountered the same problem with the Internet it is likely an issue with the cable or DSL modem, network router, or ISP. But, if only one computer is disconnecting and reconnecting, it's likely a problem with the computer. Try checking for hardware failures in the computer or issues with the operating system, as these types of issues can result in Internet connection problems.
Hi Satcomer, thanks for the YASU advice. I now use it upon every end of day shutdown. The disconnects occur less often, like randomly about every hour or two, instead of every 10 minutes. Either YASU is solving something, something that doesn't stay solved, or theres something else.
Thanks much, Satcomer, for your reply.
.......if only one computer is disconnecting and reconnecting, it's likely a problem with the computer.....
Hi Lovely K. Yes, I agree. a Pee Cee on the same LAN continues normally during Mac disconnects. Ethernet cables, connectors are tested and good. Apple Menu, about this Mac, System Report, all normal. When the disconnect happens, there are only 2 ways I can reconnect.
(1) Full reboot
(2) Changing the System Preferences, Network, Manual IP and top listed DNS to something else, then Apply
and then doing it again. and sometimes 3 - 4 times.

It used to be said that most network problems are with the DNS, and changing the top listed DNS to another well-known DNS several times, sometimes works. The Pee Cee is set to the Sony DNS and it never misses a beat, and the Apple TV is set to and it stays up.
Thanks much, Lovely K., for your insights.