Port 9900 (iua)

IANA assigns port 9900 to iua: IUA.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

iua TCP IUA Lyndon Ong 2 -

iua UDP IUA Lyndon Ong 2 -

iua SCTP IUA Lyndon Ong 2 -

Linux: is anything listening on TCP 9900?

sudo ss -tlnp 'sport = :9900'

Linux: UDP 9900

sudo ss -ulnp 'sport = :9900'

Linux / macOS: which process owns the port

sudo lsof -nP -i :9900

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':9900 '

Windows (Command Prompt)

netstat -ano | findstr :9900

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9900 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 9900

From Windows

Test-NetConnection HOST -Port 9900

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 9900

ufw

sudo ufw deny 9900/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 9900 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 9900 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 9900' -Direction Inbound -Protocol TCP -LocalPort 9900 -Action Block

ufw

sudo ufw deny 9900/udp

iptables

sudo iptables -A INPUT -p udp --dport 9900 -j DROP

nftables

sudo nft add rule inet filter input udp dport 9900 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 9900' -Direction Inbound -Protocol UDP -LocalPort 9900 -Action Block

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