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Port 104 (acr-nema)

IANA assigns port 104 to acr-nema: ACR-NEMA Digital Imag. & Comm. 300.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
acr-nema TCP ACR-NEMA Digital Imag. & Comm. 300 Patrick McNamee -
acr-nema UDP ACR-NEMA Digital Imag. & Comm. 300 Patrick McNamee -

Check what is listening on port 104

Linux: is anything listening on TCP 104?
sudo ss -tlnp 'sport = :104'
Linux: UDP 104
sudo ss -ulnp 'sport = :104'
Linux / macOS: which process owns the port
sudo lsof -nP -i :104
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':104 '
Windows (Command Prompt)
netstat -ano | findstr :104
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 104 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 104
From Windows
Test-NetConnection HOST -Port 104
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 104

Block port 104 in the firewall

ufw
sudo ufw deny 104/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 104 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 104 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 104' -Direction Inbound -Protocol TCP -LocalPort 104 -Action Block
ufw
sudo ufw deny 104/udp
iptables
sudo iptables -A INPUT -p udp --dport 104 -j DROP
nftables
sudo nft add rule inet filter input udp dport 104 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 104' -Direction Inbound -Protocol UDP -LocalPort 104 -Action Block

Related ports

102Siemens S7 (ISO-TSAP)103gppitnp105cso, csnet-ns1063com-tsmux

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