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Port 652 (hello-port)

IANA assigns port 652 to hello-port: HELLO_PORT.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
hello-port TCP HELLO_PORT Patrick Cipiere -
hello-port UDP HELLO_PORT Patrick Cipiere -

Check what is listening on port 652

Linux: is anything listening on TCP 652?
sudo ss -tlnp 'sport = :652'
Linux: UDP 652
sudo ss -ulnp 'sport = :652'
Linux / macOS: which process owns the port
sudo lsof -nP -i :652
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':652 '
Windows (Command Prompt)
netstat -ano | findstr :652
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 652 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 652
From Windows
Test-NetConnection HOST -Port 652
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 652

Block port 652 in the firewall

ufw
sudo ufw deny 652/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 652 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 652 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 652' -Direction Inbound -Protocol TCP -LocalPort 652 -Action Block
ufw
sudo ufw deny 652/udp
iptables
sudo iptables -A INPUT -p udp --dport 652 -j DROP
nftables
sudo nft add rule inet filter input udp dport 652 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 652' -Direction Inbound -Protocol UDP -LocalPort 652 -Action Block

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