1

When I look at all the ports that are open on my computer, one of them is 53, which corresponds to DNS.

From what I understand about how DNS stuff works, my computer would normally have to ask someone else about domain name information - my ISP would be my DNS.

But if my DNS port is open (in a LISTEN state), then what does that mean? That I'm a DNS service to some other device? Are other phones on my WiFi trying to reach my computer first for DNS info before they get forwarded to the ISP's DNS, or what?

Improve this question
1
  • But if my DNS port is open (in a LISTEN state), then what does that mean? Dependent by what process is listening.
    – Akina
    May 24, 2019 at 11:34

1 Answer 1

Reset to default
3

It means either your computer is running a DNS server (or proxy or it has been compromised and someone is using it as a mechanism to control/access your system).

If port 53 is only listening on your LAN it's likely you have some computer sharing going on and this woukd be normal on a router. If it is listening on a WAN interface you probably have a problem.

Are other phones on my WiFi trying to reach my computer first for DNS info before they get forwarded to the ISP's DNS, or what?

That depends on those devices. A DNS server cannot "attract" requests by merely running; devices need to be configured to use it first.

(But if you also run a DHCP server, it can provide such configuration automatically, just as with a normal home router.)

Improve this answer
4
  • You're right, i was running a DNS server, turns out nginx runs a DNS for service discovery. nginx.com/blog/dns-service-discovery-nginx-plus
    – Digital Ninja
    May 24, 2019 at 13:49
  • @DigitalNinja: But that article talks about nginx acting as a DNS client, not a server...
    – u1686_grawity
    May 27, 2019 at 4:20
  • @grawity Which means i can afford to close the port. But nginx is what made the port be open on my computer to begin with, when i installed it, no?
    – Digital Ninja
    May 27, 2019 at 5:38
  • The article you linked does not support that theory, because a DNS client never listens on port 53. (Remember that TCP and UDP packets have 'source' and 'destination' ports.) The only reliable way to know what's listening on a port is to ask the OS itself, e.g. using sudo netstat -l -p -t -u -n on Linux, or using netstat -a -n -b on Windows.
    – u1686_grawity
    May 27, 2019 at 5:46

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .