Why Can't Change the DNS?

FreePBX Networking
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1

Hi guys,

Does anyone know what this DNS server (100.100.100.100) is and how I can change it?

Every time I save the default DNS settings, they automatically revert to this IP address.Any ideas on how to stop this from happening?

Screenshot 2026-11-11 at 16.03.39
Screenshot 2026-11-11 at 16.03.39837×357 13.2 KB

FreePBX-17
Debian - 12.15
core - 17.0.18.56
sysadmin - 17.0.3.10
framework - 17.0.33.4

Thanks!

2

What is 100.100.100.100? · Tailscale Docs What is 100.100.100.100? · Tailscale Docs
What trouble is it causing?

3

Oh yes, I do have Tailscale VPN enabled.
I haven’t noticed any issues, but normally I would expect to be able to choose which DNS servers I want to use, whether public or private, and have my settings saved without them automatically reverting.

Is this behaviour controlled by Tailscale?

Thanks!

4

Correction Sip Trunk connection tailscaled dns effected.. Stopped service and SipTrunk via FQDN registred..

5

The IP 100.100.100.100 is a Carrier-Grade NAT (CGNAT) / Cloud Provider internal resolver (frequently pushed by cloud VPS providers like Alibaba Cloud via DHCP).

Every time your network interface renews its DHCP lease or restarts NetworkManager, the cloud DHCP client overwrites /etc/resolv.conf, reverting whatever you typed in FreePBX System Admin.

Here is how to lock your preferred DNS permanently via SSH:

Option A: Force DHCP client to override DNS

Edit /etc/dhcp/dhclient.conf and add:

supersede domain-name-servers 8.8.8.8, 1.1.1.1;

Then restart the network service.

Option B: Lock /etc/resolv.conf with immutable attribute

Write your nameservers directly into /etc/resolv.conf:

cat << 'EOF' > /etc/resolv.conf
nameserver 8.8.8.8
nameserver 1.1.1.1
EOF
chattr +i /etc/resolv.conf

The +i attribute prevents DHCP scripts from modifying the file on reboot.