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// Other services

Port 321: PIP

Port 321 is assigned by IANA to pip (PIP).

321

How pip works

Other services
client:321pipresponse client:321pipresponse

The client sends a request to port 321 and the pip 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 321 dangerous?

We have no specific security note for port 321. 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 321

ServicePortTransportDescriptionReferenceUpdated
pip 321 TCP, UDP PIP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 321, and is it reachable?

Linux

sudo ss -ltnup 'sport = :321'      # process listening on 321
sudo lsof -nP -i :321

macOS

sudo lsof -nP -i :321

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 321 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 321
netstat -ano | findstr :321

From another machine

nmap -p 321 -sV <host>
sudo nmap -sU -p 321 <host>
nc -zv <host> 321

Block it in the firewall

sudo ufw deny 321/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 321" -Direction Inbound -LocalPort 321 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 321 used for?

Port 321 is assigned by IANA to pip (PIP).

Is port 321 TCP or UDP?

Port 321 is registered for TCP and UDP.

Is it safe to open port 321?

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 321 is open?

On Linux run "ss -ltnup 'sport = :321'", on macOS "lsof -nP -i :321", and on Windows "netstat -ano | findstr :321" to see the local process. From another machine, "nmap -p 321 <host>" shows whether it is reachable.

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