Checking if a port is open using Nmap doesn't work

FabArd08

I'm running NetBSD 11.0 RC4 and I want to check whether port 5353 on a host on my network is open for the UDP protocol. I'm using the following command:
nmap -sU -p 5353 192.168.1.225
I'm not getting any results.
Just to clarify, the npf firewall is not active.
Could someone tell me why this isn't working?

Jay

FabArd08 hi. Are you using sudo or directly trying with root account?

rvp

FabArd08 It works as far as I can see. What's the difference that you're seeing?

Script started on Thu Jun  4 12:25:43 2026
CoreBook# uname -mr
11.99.6 amd64

CoreBook# nmap -V
Nmap version 7.98 ( https://nmap.org )
Platform: x86_64--netbsd
Compiled with: openssl-3.5.6 libssh2-1.11.1 libz-1.3.1 libpcre2-10.47 libpcap-1.10.6 nmap-libdnet-1.18.0 ipv6
Compiled without: liblua
Available nsock engines: kqueue poll select

CoreBook# nmap -sU -p 53 192.168.68.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 12:26 +0000
Nmap scan report for gateway.local (192.168.68.1)
Host is up (0.0033s latency).

PORT   STATE SERVICE
53/udp open  domain
MAC Address: D8:47:32:A8:B2:88 (TP-Link Technologies)

Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds

CoreBook# nmap -sU -p 555 192.168.68.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 12:26 +0000
Nmap scan report for gateway.local (192.168.68.1)
Host is up (0.0037s latency).

PORT    STATE  SERVICE
555/udp closed dsf
MAC Address: D8:47:32:A8:B2:88 (TP-Link Technologies)

Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds

CoreBook# ^D

Script done on Thu Jun  4 12:26:55 2026

(The session above was run on 11.99.6, but, the output is the same for 11.0_RC4/amd64 in QEMU.)

FabArd08

I use it as root with the su- command

FabArd08

I tried it on a fresh 10.1 installation, and it doesn't work there either.

FabArd08

uname -mr
10.1 amd64

nmap -v
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 15:10 +0200
Read data files from: /usr/pkg/bin/../share/nmap
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 0.08 seconds
           Raw packets sent: 0 (0B) | Rcvd: 0 (0B)

nmap -sU -p 53 192.168.1.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 15:18 +0200
^C

I exited the command with CTRL-C because it wasn't displaying anything

nmap -sU -p 555 192.168.1.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 15:33 +0200
^C

I exited the command with CTRL-C because it wasn't displaying anything

The only IP address that works is 127.0.0.1:

nmap -sU -p 53 127.0.0.1
Starting Nmap 7.98 ( https://nmap.org ) at 2026-06-04 15:35 +0200
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000033s latency).

PORT    STATE SERVICE
53/udp closed domain

Nmap done: 1 IP address (1 host up) scanned in 1.31 seconds

Just to clarify, I'm using the iwn0 network interface