Port 4200 (Angular dev server)

Default port of ng serve (Angular CLI). IANA lists 4200-4299 for VRML multi-user systems.

Registered (user) port, 1024-49151 TCP Development tools Localhost or LAN only

What port 4200 is used for

Default port of ng serve (Angular CLI). IANA lists 4200-4299 for VRML multi-user systems.

Localhost or LAN only. Development only; keep it on localhost.

Port 4200 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 4200?

sudo ss -tlnp 'sport = :4200'

Linux / macOS: which process owns the port

sudo lsof -nP -i :4200

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':4200 '

Windows (Command Prompt)

netstat -ano | findstr :4200

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4200 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 4200

From Windows

Test-NetConnection HOST -Port 4200

ufw

sudo ufw deny 4200/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 4200 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 4200 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 4200' -Direction Inbound -Protocol TCP -LocalPort 4200 -Action Block

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