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Port 25901 (niobserver)

IANA assigns port 25901 to niobserver: NIObserver.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
niobserver TCP NIObserver Roman Oliynyk -
niobserver UDP NIObserver Roman Oliynyk -

Check what is listening on port 25901

Linux: is anything listening on TCP 25901?
sudo ss -tlnp 'sport = :25901'
Linux: UDP 25901
sudo ss -ulnp 'sport = :25901'
Linux / macOS: which process owns the port
sudo lsof -nP -i :25901
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':25901 '
Windows (Command Prompt)
netstat -ano | findstr :25901
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 25901 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 25901
From Windows
Test-NetConnection HOST -Port 25901
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 25901

Block port 25901 in the firewall

ufw
sudo ufw deny 25901/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 25901 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 25901 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 25901' -Direction Inbound -Protocol TCP -LocalPort 25901 -Action Block
ufw
sudo ufw deny 25901/udp
iptables
sudo iptables -A INPUT -p udp --dport 25901 -j DROP
nftables
sudo nft add rule inet filter input udp dport 25901 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 25901' -Direction Inbound -Protocol UDP -LocalPort 25901 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.