- 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 1991: cisco STUN Priority 2 port
Port 1991 is assigned by IANA to stun-p2 (cisco STUN Priority 2 port).
1991
How stun-p2 works
Voice & chatPort 1991 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 1991 dangerous?
We have no specific security note for port 1991. Its risk depends on the program actually listening on it. General advice for voice & chat services:
IANA registry entries for port 1991
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| stun-p2 | 1991 | TCP, UDP | cisco STUN Priority 2 port | - | - |
// source: IANA service name and port number registry
Which program uses port 1991, and is it reachable?
Linux
sudo ss -ltnup 'sport = :1991' # process listening on 1991
sudo lsof -nP -i :1991macOS
sudo lsof -nP -i :1991
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1991 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 1991 netstat -ano | findstr :1991
From another machine
nmap -p 1991 -sV <host> sudo nmap -sU -p 1991 <host> nc -zv <host> 1991
Block it in the firewall
sudo ufw deny 1991/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 1991" -Direction Inbound -LocalPort 1991 -Protocol TCP -Action Block # Windows
What is port 1991 used for?
Port 1991 is assigned by IANA to stun-p2 (cisco STUN Priority 2 port).
Is port 1991 TCP or UDP?
Port 1991 is registered for TCP and UDP.
Is it safe to open port 1991?
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 1991 is open?
On Linux run "ss -ltnup 'sport = :1991'", on macOS "lsof -nP -i :1991", and on Windows "netstat -ano | findstr :1991" to see the local process. From another machine, "nmap -p 1991 <host>" shows whether it is reachable.