HTTPfy

Port 9999 (distinct)

IANA assigns port 9999 to distinct.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
distinct TCP distinct Anoop Tewari -
distinct UDP distinct Anoop Tewari -

Check what is listening on port 9999

Linux: is anything listening on TCP 9999?
sudo ss -tlnp 'sport = :9999'
Linux: UDP 9999
sudo ss -ulnp 'sport = :9999'
Linux / macOS: which process owns the port
sudo lsof -nP -i :9999
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':9999 '
Windows (Command Prompt)
netstat -ano | findstr :9999
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 9999 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 9999
From Windows
Test-NetConnection HOST -Port 9999
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 9999

Block port 9999 in the firewall

ufw
sudo ufw deny 9999/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 9999 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 9999 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 9999' -Direction Inbound -Protocol TCP -LocalPort 9999 -Action Block
ufw
sudo ufw deny 9999/udp
iptables
sudo iptables -A INPUT -p udp --dport 9999 -j DROP
nftables
sudo nft add rule inet filter input udp dport 9999 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 9999' -Direction Inbound -Protocol UDP -LocalPort 9999 -Action Block

Related ports

9997Splunk forwarder receiving9998distinct3210000Webmin10001scp-config

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