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// Other services

Port 401: Uninterruptible Power Supply

Port 401 is assigned by IANA to ups (Uninterruptible Power Supply).

401

How ups works

Other services
client:401upsresponse client:401upsresponse

The client sends a request to port 401 and the ups 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 401 dangerous?

We have no specific security note for port 401. 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 401

ServicePortTransportDescriptionReferenceUpdated
ups 401 TCP, UDP Uninterruptible Power Supply - 2008-08-29

// source: IANA service name and port number registry

03 Check it

Which program uses port 401, and is it reachable?

Linux

sudo ss -ltnup 'sport = :401'      # process listening on 401
sudo lsof -nP -i :401

macOS

sudo lsof -nP -i :401

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 401 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 401
netstat -ano | findstr :401

From another machine

nmap -p 401 -sV <host>
sudo nmap -sU -p 401 <host>
nc -zv <host> 401

Block it in the firewall

sudo ufw deny 401/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 401" -Direction Inbound -LocalPort 401 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 401 used for?

Port 401 is assigned by IANA to ups (Uninterruptible Power Supply).

Is port 401 TCP or UDP?

Port 401 is registered for TCP and UDP.

Is it safe to open port 401?

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 401 is open?

On Linux run "ss -ltnup 'sport = :401'", on macOS "lsof -nP -i :401", and on Windows "netstat -ano | findstr :401" to see the local process. From another machine, "nmap -p 401 <host>" shows whether it is reachable.

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