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// Other services

Port 533: for emergency broadcasts

Port 533 is assigned by IANA to netwall (for emergency broadcasts).

533

How netwall works

Other services
client:533netwallresponse client:533netwallresponse

The client sends a request to port 533 and the netwall service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 533 dangerous?

We have no specific security note for port 533. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 533

ServicePortTransportDescriptionReferenceUpdated
netwall 533 TCP, UDP for emergency broadcasts - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 533, and is it reachable?

Linux

sudo ss -ltnup 'sport = :533'      # process listening on 533
sudo lsof -nP -i :533

macOS

sudo lsof -nP -i :533

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 533 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 533
netstat -ano | findstr :533

From another machine

nmap -p 533 -sV <host>
sudo nmap -sU -p 533 <host>
nc -zv <host> 533

Block it in the firewall

sudo ufw deny 533/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 533" -Direction Inbound -LocalPort 533 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 533 used for?

Port 533 is assigned by IANA to netwall (for emergency broadcasts).

Is port 533 TCP or UDP?

Port 533 is registered for TCP and UDP.

Is it safe to open port 533?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 533 is open?

On Linux run "ss -ltnup 'sport = :533'", on macOS "lsof -nP -i :533", and on Windows "netstat -ano | findstr :533" to see the local process. From another machine, "nmap -p 533 <host>" shows whether it is reachable.

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