HTTPfy

Port 533 (netwall)

IANA assigns port 533 to netwall: for emergency broadcasts.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
netwall TCP for emergency broadcasts Andreas Heidemann -
netwall UDP for emergency broadcasts Andreas Heidemann -

Check what is listening on port 533

Linux: is anything listening on TCP 533?
sudo ss -tlnp 'sport = :533'
Linux: UDP 533
sudo ss -ulnp 'sport = :533'
Linux / macOS: which process owns the port
sudo lsof -nP -i :533
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':533 '
Windows (Command Prompt)
netstat -ano | findstr :533
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 533 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 533
From Windows
Test-NetConnection HOST -Port 533
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 533

Block port 533 in the firewall

ufw
sudo ufw deny 533/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 533 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 533 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 533' -Direction Inbound -Protocol TCP -LocalPort 533 -Action Block
ufw
sudo ufw deny 533/udp
iptables
sudo iptables -A INPUT -p udp --dport 533 -j DROP
nftables
sudo nft add rule inet filter input udp dport 533 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 533' -Direction Inbound -Protocol UDP -LocalPort 533 -Action Block

Related ports

531conference532netnews534windream535iiop

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