HTTPfy

Port 4000 (terabase)

IANA assigns port 4000 to terabase: Terabase.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
terabase TCP Terabase
Potential Conflict of ports PORT 4000 also used by ICQ <www.icq.com> Thor Olson -
terabase UDP Terabase
Potential Conflict of ports PORT 4000 also used by ICQ <www.icq.com> Thor Olson -

Check what is listening on port 4000

Linux: is anything listening on TCP 4000?
sudo ss -tlnp 'sport = :4000'
Linux: UDP 4000
sudo ss -ulnp 'sport = :4000'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4000
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4000 '
Windows (Command Prompt)
netstat -ano | findstr :4000
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4000 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4000
From Windows
Test-NetConnection HOST -Port 4000
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4000

Block port 4000 in the firewall

ufw
sudo ufw deny 4000/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4000 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4000 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4000' -Direction Inbound -Protocol TCP -LocalPort 4000 -Action Block
ufw
sudo ufw deny 4000/udp
iptables
sudo iptables -A INPUT -p udp --dport 4000 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4000 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4000' -Direction Inbound -Protocol UDP -LocalPort 4000 -Action Block

Related ports

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