- 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 1720: H.323 Call Control Signalling
Port 1720 is assigned by IANA to h323hostcall (H.323 Call Control Signalling).
1720
How h323hostcall works
Voice & chatPort 1720 sets up the call (who calls whom), then the voice travels as a stream of audio packets.
- Transport
- TCP · UDP · SCTP
- 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 1720 dangerous?
We have no specific security note for port 1720. Its risk depends on the program actually listening on it. General advice for voice & chat services:
IANA registry entries for port 1720
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| h323hostcall | 1720 | TCP, UDP, SCTP | H.323 Call Control Signalling | - | 2013-01-31 |
// source: IANA service name and port number registry
Which program uses port 1720, and is it reachable?
Linux
sudo ss -ltnup 'sport = :1720' # process listening on 1720
sudo lsof -nP -i :1720macOS
sudo lsof -nP -i :1720
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1720 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 1720 netstat -ano | findstr :1720
From another machine
nmap -p 1720 -sV <host> sudo nmap -sU -p 1720 <host> nc -zv <host> 1720
Block it in the firewall
sudo ufw deny 1720/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 1720" -Direction Inbound -LocalPort 1720 -Protocol TCP -Action Block # Windows
What is port 1720 used for?
Port 1720 is assigned by IANA to h323hostcall (H.323 Call Control Signalling).
Is port 1720 TCP or UDP?
Port 1720 is registered for TCP and UDP and SCTP.
Is it safe to open port 1720?
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 1720 is open?
On Linux run "ss -ltnup 'sport = :1720'", on macOS "lsof -nP -i :1720", and on Windows "netstat -ano | findstr :1720" to see the local process. From another machine, "nmap -p 1720 <host>" shows whether it is reachable.