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Port 423 (opc-job-start)

IANA assigns port 423 to opc-job-start: IBM Operations Planning and Control Start.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
opc-job-start TCP IBM Operations Planning and Control Start - -
opc-job-start UDP IBM Operations Planning and Control Start - -

Check what is listening on port 423

Linux: is anything listening on TCP 423?
sudo ss -tlnp 'sport = :423'
Linux: UDP 423
sudo ss -ulnp 'sport = :423'
Linux / macOS: which process owns the port
sudo lsof -nP -i :423
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':423 '
Windows (Command Prompt)
netstat -ano | findstr :423
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 423 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 423
From Windows
Test-NetConnection HOST -Port 423
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 423

Block port 423 in the firewall

ufw
sudo ufw deny 423/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 423 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 423 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 423' -Direction Inbound -Protocol TCP -LocalPort 423 -Action Block
ufw
sudo ufw deny 423/udp
iptables
sudo iptables -A INPUT -p udp --dport 423 -j DROP
nftables
sudo nft add rule inet filter input udp dport 423 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 423' -Direction Inbound -Protocol UDP -LocalPort 423 -Action Block

Related ports

421ariel2422ariel3424opc-job-track425icad-el

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