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Port 33331 (diamondport)

IANA assigns port 33331 to diamondport: DiamondCentral Interface.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
diamondport TCP DiamondCentral Interface Edward Browdy -
diamondport UDP DiamondCentral Interface Edward Browdy -

Registry dates for this port: registered 2002-07.

Check what is listening on port 33331

Linux: is anything listening on TCP 33331?
sudo ss -tlnp 'sport = :33331'
Linux: UDP 33331
sudo ss -ulnp 'sport = :33331'
Linux / macOS: which process owns the port
sudo lsof -nP -i :33331
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':33331 '
Windows (Command Prompt)
netstat -ano | findstr :33331
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 33331 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 33331
From Windows
Test-NetConnection HOST -Port 33331
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 33331

Block port 33331 in the firewall

ufw
sudo ufw deny 33331/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 33331 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 33331 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 33331' -Direction Inbound -Protocol TCP -LocalPort 33331 -Action Block
ufw
sudo ufw deny 33331/udp
iptables
sudo iptables -A INPUT -p udp --dport 33331 -j DROP
nftables
sudo nft add rule inet filter input udp dport 33331 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 33331' -Direction Inbound -Protocol UDP -LocalPort 33331 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.