Windows 10 DNS oddity

General
1

I have had a DNS problem which I don't understand so I am turning to the experts here.

I am running a pi on my domestic network which is hosting DHCP, pihole and a backup service. Pihole version is: Pi-hole Version v4.4 (Update available!) Web Interface Version v4.3.3 (Update available!) FTL Version v4.3.1 (Update available!)

On Thursday evening I had an oddity. My Dell laptop (Windows 10) just could not access the Internet. I could access lan services like the NAS and the router etc. I could ping 192.168.x.y addresses and 8.8.8.8 (an external DNS server) but not google.com.
An ipconfig/flushdns and laptop reboots did not help, nor a reboot of the pi.

However, every other device in the house worked fine. Phones, ipad, Android tablet, Mythtv, TV and the other Windows 10 system all worked normally and were able to access Internet. To my mind this exonerates pihole.

Friday morning, I had the same problem but on power up in the afternoon all was working fine again.

I cannot find the google pings in the pihole log, but the laptop it did have accesses to fallback.nos-avg.cz (unexpected) and accesses to the Avast site su.ff.avast.com (quite expected). The avg ones were two every 30 to 40 secs.

I am running Avast but not AVG. It looks just as if something on the laptop was hi-jacking DNS requests!

An Avast virus scan of the laptop is clear and I've now blocked fallback.nos-avg.cz.

Can anyone explain all this? I'd appreciate any insight into this oddity.

Phil

2

Check your AVAST for a feature called RealSite, which will have your laptop use a DNS server owned and operated by AVAST in addition to Pi-hole. It's worth noting that you may expose your DNS history to AVAST this way.

Normally, we receive complaints about RealSite providing DNS resolution for domains blocked by Pi-hole (see e.g. Hilfe: Windows löst Hostname auch ohne PiHole auf? - #26 by Chris80).
But if their DNS server is down or you have blocked access to their server, then DNS resolution may also fail in circumstances.

Try disabling AVAST RealSite and see if this solves your issue.

1 Like
3

Thanks or the reply. That's interesting.
I'm using the free version of Avast which does not include that feature and the control panel confirms that.
However, I'm inclined to believe that the feature might be used during updates and Avast is still my chief suspect!
Computer is still back to normal.
Phil.

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