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Port 3901 (nimsh)

IANA assigns port 3901 to nimsh: NIM Service Handler.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
nimsh TCP NIM Service Handler Paul B Finley -
nimsh UDP NIM Service Handler Paul B Finley -

Registry dates for this port: registered 2003-10.

Check what is listening on port 3901

Linux: is anything listening on TCP 3901?
sudo ss -tlnp 'sport = :3901'
Linux: UDP 3901
sudo ss -ulnp 'sport = :3901'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3901
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3901 '
Windows (Command Prompt)
netstat -ano | findstr :3901
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3901 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3901
From Windows
Test-NetConnection HOST -Port 3901
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3901

Block port 3901 in the firewall

ufw
sudo ufw deny 3901/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3901 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3901 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3901' -Direction Inbound -Protocol TCP -LocalPort 3901 -Action Block
ufw
sudo ufw deny 3901/udp
iptables
sudo iptables -A INPUT -p udp --dport 3901 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3901 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3901' -Direction Inbound -Protocol UDP -LocalPort 3901 -Action Block

Related ports

3899itv-control3900udt-os, udt_os3902nimaux3903charsetmgr

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.