Found below by accident:
```
pi@ph5:~ $ man dnsmasq
[..]
--dns-loop-detect
Enable code to detect DNS forwarding loops; ie the situa‐
tion where a query sent to one of the upstream server
eventually returns as a new query to the dnsmasq instance.
The process works by generating TXT queries of the form
<hex>.test and sending them to each upstream server. The
hex is a UID which encodes the instance of dnsmasq sending
the query and the upstream server to which it was sent. If
the query returns to the server which sent it, then the
upstream server through which it was sent is disabled and
this event is logged. Each time the set of upstream
servers changes, the test is re-run on all of them, in‐
cluding ones which were previously disabled.
```
Seems to work just fine if I point my router 10.0.0.1 back to Pi-hole in the WAN DNS settings:
```
pi@ph5:~ $ grep server= -R /etc/dnsmasq.*
/etc/dnsmasq.d/01-pihole.conf:server=9.9.9.10
/etc/dnsmasq.d/01-pihole.conf:server=149.112.112.10
/etc/dnsmasq.d/01-pihole.conf:server=10.0.0.1
/etc/dnsmasq.d/01-pihole.conf:rev-server=10.0.0.0/24,10.0.0.2
/etc/dnsmasq.d/01-pihole.conf:server=/dehakkelaar.nl/10.0.0.2
/etc/dnsmasq.d/01-pihole.conf:server=/use-application-dns.net/
```
```
pi@ph5:~ $ sudo tee /etc/dnsmasq.d/99-my-settings.conf <<< $'dns-loop-detect'
dns-loop-detect
```
```
pi@ph5:~ $ pihole restartdns
[✓] Restarting DNS server
```
```
pi@ph5:~ $ tail -F /var/log/pihole.log
[..]
Oct 22 18:17:41 dnsmasq[17301]: using nameserver 10.0.0.2#53 for domain dehakkelaar.nl
Oct 22 18:17:41 dnsmasq[17301]: using nameserver 10.0.0.2#53 for domain 0.0.10.in-addr.arpa
Oct 22 18:17:41 dnsmasq[17301]: NOT using nameserver 10.0.0.1#53 - query loop detected
Oct 22 18:17:41 dnsmasq[17301]: using nameserver 149.112.112.10#53
Oct 22 18:17:41 dnsmasq[17301]: using nameserver 9.9.9.10#53
```
In the case that FTL is started under root, dnsmasq changes the user to
pihole due to this setting. The shared memory is created before this
switch, and may cause issues such as failing to delete or reallocate
the shared memory.
These config lines were necessary before dnsmasq became part of FTL, but
now since dnsmasq runs under FTL, we can configure the user/group
through FTL.
Signed-off-by: Mcat12 <newtoncat12@yahoo.com>
Prep for using sed to insert user selected DNSs into 01-pihole.conf.
Selections will come from dialog during install script containing the
following choices: Google, DynDNS, and eventually 2 custom DNS servers.
Christian König