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Port 3330 (mcs-calypsoicf)

IANA assigns port 3330 to mcs-calypsoicf: MCS Calypso ICF.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
mcs-calypsoicf TCP MCS Calypso ICF - -
mcs-calypsoicf UDP MCS Calypso ICF - -

Check what is listening on port 3330

Linux: is anything listening on TCP 3330?
sudo ss -tlnp 'sport = :3330'
Linux: UDP 3330
sudo ss -ulnp 'sport = :3330'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3330
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3330 '
Windows (Command Prompt)
netstat -ano | findstr :3330
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3330 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3330
From Windows
Test-NetConnection HOST -Port 3330
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3330

Block port 3330 in the firewall

ufw
sudo ufw deny 3330/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3330 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3330 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3330' -Direction Inbound -Protocol TCP -LocalPort 3330 -Action Block
ufw
sudo ufw deny 3330/udp
iptables
sudo iptables -A INPUT -p udp --dport 3330 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3330 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3330' -Direction Inbound -Protocol UDP -LocalPort 3330 -Action Block

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