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// Other services

Port 2123: GTP-Control Plane (3GPP)

Port 2123 is assigned by IANA to gtp-control (GTP-Control Plane (3GPP)).

2123

How gtp-control works

Other services
client:2123gtp-controlresponse client:2123gtp-controlresponse

The client sends a request to port 2123 and the gtp-control 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
Registered (1024-49151)
Category
Other services
01 Security

Is port 2123 dangerous?

We have no specific security note for port 2123. 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 2123

ServicePortTransportDescriptionReferenceUpdated
gtp-control 2123 TCP, UDP GTP-Control Plane (3GPP) - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 2123, and is it reachable?

Linux

sudo ss -ltnup 'sport = :2123'      # process listening on 2123
sudo lsof -nP -i :2123

macOS

sudo lsof -nP -i :2123

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 2123 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 2123
netstat -ano | findstr :2123

From another machine

nmap -p 2123 -sV <host>
sudo nmap -sU -p 2123 <host>
nc -zv <host> 2123

Block it in the firewall

sudo ufw deny 2123/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 2123" -Direction Inbound -LocalPort 2123 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 2123 used for?

Port 2123 is assigned by IANA to gtp-control (GTP-Control Plane (3GPP)).

Is port 2123 TCP or UDP?

Port 2123 is registered for TCP and UDP.

Is it safe to open port 2123?

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 2123 is open?

On Linux run "ss -ltnup 'sport = :2123'", on macOS "lsof -nP -i :2123", and on Windows "netstat -ano | findstr :2123" to see the local process. From another machine, "nmap -p 2123 <host>" shows whether it is reachable.

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