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// Other services

Port 661: HAP

Port 661 is assigned by IANA to hap (HAP).

661

How hap works

Other services
client:661hapresponse client:661hapresponse

The client sends a request to port 661 and the hap service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 661 dangerous?

We have no specific security note for port 661. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 661

ServicePortTransportDescriptionReferenceUpdated
hap 661 TCP, UDP HAP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 661, and is it reachable?

Linux

sudo ss -ltnup 'sport = :661'      # process listening on 661
sudo lsof -nP -i :661

macOS

sudo lsof -nP -i :661

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 661 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 661
netstat -ano | findstr :661

From another machine

nmap -p 661 -sV <host>
sudo nmap -sU -p 661 <host>
nc -zv <host> 661

Block it in the firewall

sudo ufw deny 661/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 661" -Direction Inbound -LocalPort 661 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 661 used for?

Port 661 is assigned by IANA to hap (HAP).

Is port 661 TCP or UDP?

Port 661 is registered for TCP and UDP.

Is it safe to open port 661?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 661 is open?

On Linux run "ss -ltnup 'sport = :661'", on macOS "lsof -nP -i :661", and on Windows "netstat -ano | findstr :661" to see the local process. From another machine, "nmap -p 661 <host>" shows whether it is reachable.

05 Related
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