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// Other services

Port 3321: VNSSTR

Port 3321 is assigned by IANA to vnsstr (VNSSTR).

3321

How vnsstr works

Other services
client:3321vnsstrresponse client:3321vnsstrresponse

The client sends a request to port 3321 and the vnsstr 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 3321 dangerous?

We have no specific security note for port 3321. 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 3321

ServicePortTransportDescriptionReferenceUpdated
vnsstr 3321 TCP, UDP VNSSTR - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3321, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3321'      # process listening on 3321
sudo lsof -nP -i :3321

macOS

sudo lsof -nP -i :3321

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3321 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3321
netstat -ano | findstr :3321

From another machine

nmap -p 3321 -sV <host>
sudo nmap -sU -p 3321 <host>
nc -zv <host> 3321

Block it in the firewall

sudo ufw deny 3321/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3321" -Direction Inbound -LocalPort 3321 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3321 used for?

Port 3321 is assigned by IANA to vnsstr (VNSSTR).

Is port 3321 TCP or UDP?

Port 3321 is registered for TCP and UDP.

Is it safe to open port 3321?

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 3321 is open?

On Linux run "ss -ltnup 'sport = :3321'", on macOS "lsof -nP -i :3321", and on Windows "netstat -ano | findstr :3321" to see the local process. From another machine, "nmap -p 3321 <host>" shows whether it is reachable.

05 Related
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