CyberHunter
Local dataset, no network
// Other services

Port 900: OMG Initial Refs

Port 900 is assigned by IANA to omginitialrefs (OMG Initial Refs).

900

How omginitialrefs works

Other services
client:900omginitialrefsresponse client:900omginitialrefsresponse

The client sends a request to port 900 and the omginitialrefs 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 900 dangerous?

We have no specific security note for port 900. 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 900

ServicePortTransportDescriptionReferenceUpdated
omginitialrefs 900 TCP, UDP OMG Initial Refs - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 900, and is it reachable?

Linux

sudo ss -ltnup 'sport = :900'      # process listening on 900
sudo lsof -nP -i :900

macOS

sudo lsof -nP -i :900

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 900 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 900
netstat -ano | findstr :900

From another machine

nmap -p 900 -sV <host>
sudo nmap -sU -p 900 <host>
nc -zv <host> 900

Block it in the firewall

sudo ufw deny 900/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 900" -Direction Inbound -LocalPort 900 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 900 used for?

Port 900 is assigned by IANA to omginitialrefs (OMG Initial Refs).

Is port 900 TCP or UDP?

Port 900 is registered for TCP and UDP.

Is it safe to open port 900?

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 900 is open?

On Linux run "ss -ltnup 'sport = :900'", on macOS "lsof -nP -i :900", and on Windows "netstat -ano | findstr :900" to see the local process. From another machine, "nmap -p 900 <host>" shows whether it is reachable.

05 Related
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