My mid 2011 mac running high sierra 10.13.06 keeps dropping me off the internet

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

Do you have any Bus powered USB devices plugged in?

Is your WiFi router or your Mac sitting next to a USB3 device? A poorly electrically shielded USB3 device or cable can cause WiFi interference.

A 2.4GHz cordless phone or 2.4GHz baby monitor can cause WiFi interference. These could be your own, or a neighbor if you live very close by (or in a condo/apartment).

A Microwave oven operates at 2.4GHz (it is the frequency water vibrates at, and one of the reason WiFi was giving the 2.4GHz band, as water vapor in the air interferes with long range 2.4GHz communications). Anyway, a Microwave oven that is leaking 2.4GHz microwaves could interfere, or if your router is sitting on top of or next to your Microwave and you are using the Microwave.

Make a New Location, Using network locations in Mac OS X ...

http://support.apple.com/kb/HT2712


System Preferences>Network, top of window>Locations>Edit Locations, little plus icon, give it a name.

System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.

The interface that connects to the Internet should be dragged to the top of the list.


If using Wifi, instead of joining your Network from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.

System Preferences>Network>choose interface>Advanced>Proxies Tab, make sure none are set, like for HTTP & HTTPS.

System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9

Apply.

OK, thanks for the report! :)