- Use strong credentials and TLS for signalling.
- Rate-limit registrations to stop extension scanning and toll fraud.
- Alert on unexpected chat protocols leaving servers (possible command and control).
Port 11720: H.323 Call Control Signalling Alternate
Port 11720 is assigned by IANA to h323callsigalt (H.323 Call Control Signalling Alternate).
11720
How h323callsigalt works
Voice & chatPort 11720 sets up the call (who calls whom), then the voice travels as a stream of audio packets.
- 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
- Voice & chat
Is port 11720 dangerous?
We have no specific security note for port 11720. Its risk depends on the program actually listening on it. General advice for voice & chat services:
IANA registry entries for port 11720
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| h323callsigalt | 11720 | TCP, UDP | H.323 Call Control Signalling Alternate | - | 2013-01-31 |
// source: IANA service name and port number registry
Which program uses port 11720, and is it reachable?
Linux
sudo ss -ltnup 'sport = :11720' # process listening on 11720
sudo lsof -nP -i :11720macOS
sudo lsof -nP -i :11720
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 11720 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 11720 netstat -ano | findstr :11720
From another machine
nmap -p 11720 -sV <host> sudo nmap -sU -p 11720 <host> nc -zv <host> 11720
Block it in the firewall
sudo ufw deny 11720/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 11720" -Direction Inbound -LocalPort 11720 -Protocol TCP -Action Block # Windows
What is port 11720 used for?
Port 11720 is assigned by IANA to h323callsigalt (H.323 Call Control Signalling Alternate).
Is port 11720 TCP or UDP?
Port 11720 is registered for TCP and UDP.
Is it safe to open port 11720?
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. Use strong credentials and TLS for signalling.
How do I check if port 11720 is open?
On Linux run "ss -ltnup 'sport = :11720'", on macOS "lsof -nP -i :11720", and on Windows "netstat -ano | findstr :11720" to see the local process. From another machine, "nmap -p 11720 <host>" shows whether it is reachable.