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Port 3666 (eserver-pap)

IANA assigns port 3666 to eserver-pap: IBM eServer PAP.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
eserver-pap TCP IBM eServer PAP Dave Gimpl -
eserver-pap UDP IBM EServer PAP Dave Gimpl -

Registry dates for this port: registered 2003-01.

Check what is listening on port 3666

Linux: is anything listening on TCP 3666?
sudo ss -tlnp 'sport = :3666'
Linux: UDP 3666
sudo ss -ulnp 'sport = :3666'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3666
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3666 '
Windows (Command Prompt)
netstat -ano | findstr :3666
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3666 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3666
From Windows
Test-NetConnection HOST -Port 3666
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3666

Block port 3666 in the firewall

ufw
sudo ufw deny 3666/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3666 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3666 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3666' -Direction Inbound -Protocol TCP -LocalPort 3666 -Action Block
ufw
sudo ufw deny 3666/udp
iptables
sudo iptables -A INPUT -p udp --dport 3666 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3666 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3666' -Direction Inbound -Protocol UDP -LocalPort 3666 -Action Block

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