I have been having intermittent problems connecting to the internet. When I find what I think is a resolution it works OK for a bit and then I lose connectivity again. The next "fix" seems to work and then off we go again. (I have detailed below the various things I have tried).
I am using an iMac with Sierra. The DNS setting is 10.8.0.1. I have tried updating to something more stable (eg. 126.96.36.199 and 188.8.131.52) but it reverts to 10.8.0.1 - sometimes as I am updating the setting, always within a minute or two. I have several other internet connected devices that do not have this problem so I am confident the problems lies with this computer. They were all using the same flakey DNS but have allowed me to update them to the google ones.
I have run malwarebytes, but that hasn't detected anything.
To begin with all I had to do was switch wifi off and on again and it would be ok, Once that stopped resolving the issue I needed to shut down the mac. Next I ran
sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder.
Starting in safe mode worked a few times.
Then a PRAM reset worked for a couple of times.
Then unloading and reloading mDNSResponder.plist worked a couple of days ago.
Now I try all and any combination of the above (plus swearing at it a lot), sometimes it connects other times it doesnt so I just give up!
Please help, let me know if you need anything else or if I should be posting this elsewhere