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// Other services

Port 4503: M-Bus-OMS over UDP

Port 4503 is assigned by IANA to m-bus-oms (M-Bus-OMS over UDP).

4503

How m-bus-oms works

Other services
client:4503m-bus-omsresponse client:4503m-bus-omsresponse

The client sends a request to port 4503 and the m-bus-oms service answers.

Transport
UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 4503 dangerous?

We have no specific security note for port 4503. 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 4503

ServicePortTransportDescriptionReferenceUpdated
m-bus-oms 4503 UDP M-Bus-OMS over UDP - 2025-05-19
-4503-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 4503, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4503'      # process listening on 4503
sudo lsof -nP -i :4503

macOS

sudo lsof -nP -i :4503

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4503 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4503
netstat -ano | findstr :4503

From another machine

nmap -p 4503 -sV <host>
sudo nmap -sU -p 4503 <host>
nc -zv <host> 4503

Block it in the firewall

sudo ufw deny 4503/udp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4503" -Direction Inbound -LocalPort 4503 -Protocol UDP -Action Block  # Windows
04 FAQ
What is port 4503 used for?

Port 4503 is assigned by IANA to m-bus-oms (M-Bus-OMS over UDP).

Is port 4503 TCP or UDP?

Port 4503 is registered for UDP.

Is it safe to open port 4503?

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 4503 is open?

On Linux run "ss -ltnup 'sport = :4503'", on macOS "lsof -nP -i :4503", and on Windows "netstat -ano | findstr :4503" to see the local process. From another machine, "nmap -p 4503 <host>" shows whether it is reachable.

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