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// Other services

Port 4040: Yo.net main service

Port 4040 is assigned by IANA to yo-main (Yo.net main service).

4040

How yo-main works

Other services
client:4040yo-mainresponse client:4040yo-mainresponse

The client sends a request to port 4040 and the yo-main 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 4040 dangerous?

We have no specific security note for port 4040. 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 4040

ServicePortTransportDescriptionReferenceUpdated
yo-main 4040 TCP, UDP Yo.net main service - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 4040, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4040'      # process listening on 4040
sudo lsof -nP -i :4040

macOS

sudo lsof -nP -i :4040

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4040 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4040
netstat -ano | findstr :4040

From another machine

nmap -p 4040 -sV <host>
sudo nmap -sU -p 4040 <host>
nc -zv <host> 4040

Block it in the firewall

sudo ufw deny 4040/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4040" -Direction Inbound -LocalPort 4040 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4040 used for?

Port 4040 is assigned by IANA to yo-main (Yo.net main service).

Is port 4040 TCP or UDP?

Port 4040 is registered for TCP and UDP.

Is it safe to open port 4040?

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 4040 is open?

On Linux run "ss -ltnup 'sport = :4040'", on macOS "lsof -nP -i :4040", and on Windows "netstat -ano | findstr :4040" to see the local process. From another machine, "nmap -p 4040 <host>" shows whether it is reachable.

05 Related
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