I ran an “nmap -sUV -F” on my droplet, from the outside, and it returned the following:
Port state service version
53/udp open domain dnsmasq 2.90
Im running Debian 12. My firewall is solid. I first thought may be my outgoing rules to connect to the digitalocean dns servers was causing it. I removed the rules that allow for dns lookups and even tested it with an apt update and it failed like it should. So I did a “netstat -tulnp | grep 53” and got the following results:
udp 0 0 127.0.0.54:53 0.0.0.0:* 401/systemd-resolve
udp 0 0 127.0.0.53:53 0.0.0.0:* 401/systemd-resolve
udp 0 0 0.0.0.0:5355 0.0.0.0:* 401/systemd-resolve
My research indicates that the culprit is 127.0.0.53:53 through systemd-resolve process. But how is the outside world getting a response from a loopback address since the all addresses setting 0 0.0.0.0:5355 is port 5355 an not port 53 ? I don’t want to start messing with dnsmasq or editing the /etc/systemd/resolved.conf. Does any one know the answer?
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