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// Other services

Port 3721: Xsync

Port 3721 is assigned by IANA to xsync (Xsync).

3721

How xsync works

Other services
client:3721xsyncresponse client:3721xsyncresponse

The client sends a request to port 3721 and the xsync 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 3721 dangerous?

We have no specific security note for port 3721. 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 3721

ServicePortTransportDescriptionReferenceUpdated
xsync 3721 TCP, UDP Xsync - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3721, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3721'      # process listening on 3721
sudo lsof -nP -i :3721

macOS

sudo lsof -nP -i :3721

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3721 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3721
netstat -ano | findstr :3721

From another machine

nmap -p 3721 -sV <host>
sudo nmap -sU -p 3721 <host>
nc -zv <host> 3721

Block it in the firewall

sudo ufw deny 3721/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3721" -Direction Inbound -LocalPort 3721 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3721 used for?

Port 3721 is assigned by IANA to xsync (Xsync).

Is port 3721 TCP or UDP?

Port 3721 is registered for TCP and UDP.

Is it safe to open port 3721?

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 3721 is open?

On Linux run "ss -ltnup 'sport = :3721'", on macOS "lsof -nP -i :3721", and on Windows "netstat -ano | findstr :3721" to see the local process. From another machine, "nmap -p 3721 <host>" shows whether it is reachable.

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