CyberHunter
Local dataset, no network
// Other services

Port 2721: Smart Diagnose

Port 2721 is assigned by IANA to smart-diagnose (Smart Diagnose).

2721

How smart-diagnose works

Other services
client:2721smart-diagnoseresponse client:2721smart-diagnoseresponse

The client sends a request to port 2721 and the smart-diagnose 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 2721 dangerous?

We have no specific security note for port 2721. 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 2721

ServicePortTransportDescriptionReferenceUpdated
smart-diagnose 2721 TCP, UDP Smart Diagnose - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 2721, and is it reachable?

Linux

sudo ss -ltnup 'sport = :2721'      # process listening on 2721
sudo lsof -nP -i :2721

macOS

sudo lsof -nP -i :2721

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 2721 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 2721
netstat -ano | findstr :2721

From another machine

nmap -p 2721 -sV <host>
sudo nmap -sU -p 2721 <host>
nc -zv <host> 2721

Block it in the firewall

sudo ufw deny 2721/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 2721" -Direction Inbound -LocalPort 2721 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 2721 used for?

Port 2721 is assigned by IANA to smart-diagnose (Smart Diagnose).

Is port 2721 TCP or UDP?

Port 2721 is registered for TCP and UDP.

Is it safe to open port 2721?

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 2721 is open?

On Linux run "ss -ltnup 'sport = :2721'", on macOS "lsof -nP -i :2721", and on Windows "netstat -ano | findstr :2721" to see the local process. From another machine, "nmap -p 2721 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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