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// Other services

Port 9123: Global Relay compliant instant messaging protocol

Port 9123 is assigned by IANA to grcp (Global Relay compliant instant messaging protocol).

9123

How grcp works

Other services
client:9123grcpresponse client:9123grcpresponse

The client sends a request to port 9123 and the grcp service answers.

Transport
TCP
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 9123 dangerous?

We have no specific security note for port 9123. 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 9123

ServicePortTransportDescriptionReferenceUpdated
grcp 9123 TCP Global Relay compliant instant messaging protocol - 2025-06-12
-9123-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 9123, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9123'      # process listening on 9123
sudo lsof -nP -i :9123

macOS

sudo lsof -nP -i :9123

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9123 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9123
netstat -ano | findstr :9123

From another machine

nmap -p 9123 -sV <host>
nc -zv <host> 9123

Block it in the firewall

sudo ufw deny 9123/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9123" -Direction Inbound -LocalPort 9123 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9123 used for?

Port 9123 is assigned by IANA to grcp (Global Relay compliant instant messaging protocol).

Is port 9123 TCP or UDP?

Port 9123 is registered for TCP.

Is it safe to open port 9123?

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 9123 is open?

On Linux run "ss -ltnup 'sport = :9123'", on macOS "lsof -nP -i :9123", and on Windows "netstat -ano | findstr :9123" to see the local process. From another machine, "nmap -p 9123 <host>" shows whether it is reachable.

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