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Port 3333 (dec-notes)

IANA assigns port 3333 to dec-notes: DEC Notes.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dec-notes TCP DEC Notes Kim Moraros -
dec-notes UDP DEC Notes Kim Moraros -

Check what is listening on port 3333

Linux: is anything listening on TCP 3333?
sudo ss -tlnp 'sport = :3333'
Linux: UDP 3333
sudo ss -ulnp 'sport = :3333'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3333
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3333 '
Windows (Command Prompt)
netstat -ano | findstr :3333
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3333 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3333
From Windows
Test-NetConnection HOST -Port 3333
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3333

Block port 3333 in the firewall

ufw
sudo ufw deny 3333/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3333 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3333 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3333' -Direction Inbound -Protocol TCP -LocalPort 3333 -Action Block
ufw
sudo ufw deny 3333/udp
iptables
sudo iptables -A INPUT -p udp --dport 3333 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3333 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3333' -Direction Inbound -Protocol UDP -LocalPort 3333 -Action Block

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3331mcs-messaging3332mcs-mailsvr3334directv-web3335directv-soft

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