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// Other services

Port 5721: Desktop Passthru Service

Port 5721 is assigned by IANA to dtpt (Desktop Passthru Service).

5721

How dtpt works

Other services
client:5721dtptresponse client:5721dtptresponse

The client sends a request to port 5721 and the dtpt 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
Registered (1024-49151)
Category
Other services
01 Security

Is port 5721 dangerous?

We have no specific security note for port 5721. 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 5721

ServicePortTransportDescriptionReferenceUpdated
dtpt 5721 TCP, UDP Desktop Passthru Service - 2005-01

// source: IANA service name and port number registry

03 Check it

Which program uses port 5721, and is it reachable?

Linux

sudo ss -ltnup 'sport = :5721'      # process listening on 5721
sudo lsof -nP -i :5721

macOS

sudo lsof -nP -i :5721

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5721 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 5721
netstat -ano | findstr :5721

From another machine

nmap -p 5721 -sV <host>
sudo nmap -sU -p 5721 <host>
nc -zv <host> 5721

Block it in the firewall

sudo ufw deny 5721/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 5721" -Direction Inbound -LocalPort 5721 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 5721 used for?

Port 5721 is assigned by IANA to dtpt (Desktop Passthru Service).

Is port 5721 TCP or UDP?

Port 5721 is registered for TCP and UDP.

Is it safe to open port 5721?

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 5721 is open?

On Linux run "ss -ltnup 'sport = :5721'", on macOS "lsof -nP -i :5721", and on Windows "netstat -ano | findstr :5721" to see the local process. From another machine, "nmap -p 5721 <host>" shows whether it is reachable.

05 Related
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