Dnsmasq binds to all interfaces and conflicts with systemd-resolved on Debian systems

[mrmarkuz]

Dnsmasq binds to all interfaces by default.
On Debian systems systemd-resolved binds to 127.0.0.53%lo:53 and 127.0.0.54:53 which conflicts with our current Dnsmasq implementation:

udp   UNCONN 0      0         127.0.0.54:53        0.0.0.0:*    users:(("systemd-resolve",pid=516,fd=20))
udp   UNCONN 0      0      127.0.0.53%lo:53        0.0.0.0:*    users:(("systemd-resolve",pid=516,fd=18))
tcp   LISTEN 0      4096   127.0.0.53%lo:53        0.0.0.0:*    users:(("systemd-resolve",pid=516,fd=19))
tcp   LISTEN 0      4096      127.0.0.54:53        0.0.0.0:*    users:(("systemd-resolve",pid=516,fd=21))

Steps to reproduce

• Install dnsmasq on a system where systemd-resolved is enabled (Debian)
• Configure and enable DNS

Expected behavior

Dnsmasq should run and provide DNS

Actual behavior

Dnsmasq conflicts with systemd-resolved and doesn't start

Proposed solution

Add the "bind-interfaces" option to expand-config in dnsmasq to just bind on the selected interfaces:

file.write("bind-interfaces\n")

Components

• Dnsmasq 1.3.0

See also

https://mattermost.nethesis.it/nethserver/pl/ad5t5ktyfj8j8jkeck5kc54m4w