Is there a way to determine that a DNS server (
dnsmasq) is or is not using 22.214.171.124?
I have a Google Nest Wifi Router, and it seems clear (in the diagnostic report) that it is prepending google's 126.96.36.199 and 188.8.131.52 DNS name servers to the name servers assigned in the cable modem's DHCP. Since the Router is using
dnsmasq, I believe my queries are effectively using quad-8, regardless of the configuration (which can be one of: Google's, ISP's, or Custom/Manual; set in the Google Wifi app).
Since 184.108.40.206 allegedly does not do IP filtering -- and I do not know if Comcast/Xfinity does IP filtering -- I don't know if it's likely I'll find a hostname that knowingly resolves differently in the two servers. I'm comfortable enough with
nslookup to know how to query a particular server (assuming no redirection in the ISP), but I don't know a good way to "know" which server is effectively being used.
I control the zones of two domains (via hostmonster and godaddy). Is there some heuristic to make a zone change and infer which upstream server resolves it? The fact that it will be caching responses makes this a little problematic.
(I have not found any
dnsmasq configuration files in the diagnostic report, and I don't have ssh access to the Router. I don't currently have an easy mechanism to sniff upstream of the Router, though that might be the only authoritative way. OSes on my private network include win10, mac, and linux, and I have remote access to multiple linux hosts elsewhere.)
My ISP's dns servers are 220.127.116.11 and 18.104.22.168 (if that helps).
Diagnostic report. The Google Nest Wifi Router has several API endpoints for providing instantaneous status (json) and a full diagnostic report (gzipped protobuf). Examples:
Prepending. Looking at the diagnostic report, it shows that
/etc/resolv.conflists 22.214.171.124 and 126.96.36.199 first, and one of
dhcpcd's parent processes is
shill --prepend-dns-servers=188.8.131.52,184.108.40.206. The current configuration is
Custom: 220.127.116.11, 18.104.22.168(primarily for this testing).
- Caching. I believe there is no mechanism in DNS to disable cached results. https://serverfault.com/q/372066.