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Port 1720 (h323hostcall)

IANA assigns port 1720 to h323hostcall: H.323 Call Control Signalling.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
h323hostcall TCP H.323 Call Control Signalling ITU-T -
h323hostcall UDP H.323 Call Control Signalling ITU-T -
h323hostcall SCTP H.323 Call Control ITU-T -

Registry dates for this port: registered 2014-07-30, last modified 2013-01-31.

Check what is listening on port 1720

Linux: is anything listening on TCP 1720?
sudo ss -tlnp 'sport = :1720'
Linux: UDP 1720
sudo ss -ulnp 'sport = :1720'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1720
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1720 '
Windows (Command Prompt)
netstat -ano | findstr :1720
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1720 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1720
From Windows
Test-NetConnection HOST -Port 1720
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1720

Block port 1720 in the firewall

ufw
sudo ufw deny 1720/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1720 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1720 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1720' -Direction Inbound -Protocol TCP -LocalPort 1720 -Action Block
ufw
sudo ufw deny 1720/udp
iptables
sudo iptables -A INPUT -p udp --dport 1720 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1720 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1720' -Direction Inbound -Protocol UDP -LocalPort 1720 -Action Block

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All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.