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Port 2123 (gtp-control)

IANA assigns port 2123 to gtp-control: GTP-Control Plane (3GPP).

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
gtp-control TCP GTP-Control Plane (3GPP) Alessio Casati -
gtp-control UDP GTP-Control Plane (3GPP) Alessio Casati -

Check what is listening on port 2123

Linux: is anything listening on TCP 2123?
sudo ss -tlnp 'sport = :2123'
Linux: UDP 2123
sudo ss -ulnp 'sport = :2123'
Linux / macOS: which process owns the port
sudo lsof -nP -i :2123
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':2123 '
Windows (Command Prompt)
netstat -ano | findstr :2123
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 2123 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 2123
From Windows
Test-NetConnection HOST -Port 2123
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 2123

Block port 2123 in the firewall

ufw
sudo ufw deny 2123/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 2123 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 2123 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 2123' -Direction Inbound -Protocol TCP -LocalPort 2123 -Action Block
ufw
sudo ufw deny 2123/udp
iptables
sudo iptables -A INPUT -p udp --dport 2123 -j DROP
nftables
sudo nft add rule inet filter input udp dport 2123 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 2123' -Direction Inbound -Protocol UDP -LocalPort 2123 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.