Port 4222 (NATS)

NATS client connections; 6222 is cluster routing and 8222 the HTTP monitoring port.

Registered (user) port, 1024-49151 TCP Message queues Do not expose to the internet

What port 4222 is used for

NATS client connections; 6222 is cluster routing and 8222 the HTTP monitoring port.

Do not expose to the internet. Configure authentication (tokens, NKeys or JWT) and TLS before allowing any external client.

Port 4222 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 4222?

sudo ss -tlnp 'sport = :4222'

Linux / macOS: which process owns the port

sudo lsof -nP -i :4222

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':4222 '

Windows (Command Prompt)

netstat -ano | findstr :4222

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4222 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 4222

From Windows

Test-NetConnection HOST -Port 4222

ufw

sudo ufw deny 4222/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 4222 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 4222 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 4222' -Direction Inbound -Protocol TCP -LocalPort 4222 -Action Block

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