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Port 661 (hap)

IANA assigns port 661 to hap: HAP.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
hap TCP HAP Igor Plotnikov -
hap UDP HAP Igor Plotnikov -

Check what is listening on port 661

Linux: is anything listening on TCP 661?
sudo ss -tlnp 'sport = :661'
Linux: UDP 661
sudo ss -ulnp 'sport = :661'
Linux / macOS: which process owns the port
sudo lsof -nP -i :661
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':661 '
Windows (Command Prompt)
netstat -ano | findstr :661
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 661 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 661
From Windows
Test-NetConnection HOST -Port 661
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 661

Block port 661 in the firewall

ufw
sudo ufw deny 661/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 661 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 661 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 661' -Direction Inbound -Protocol TCP -LocalPort 661 -Action Block
ufw
sudo ufw deny 661/udp
iptables
sudo iptables -A INPUT -p udp --dport 661 -j DROP
nftables
sudo nft add rule inet filter input udp dport 661 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 661' -Direction Inbound -Protocol UDP -LocalPort 661 -Action Block

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