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// Other services

Port 3921: Herodotus Net

Port 3921 is assigned by IANA to herodotus-net (Herodotus Net).

3921

How herodotus-net works

Other services
client:3921herodotus-netresponse client:3921herodotus-netresponse

The client sends a request to port 3921 and the herodotus-net 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 3921 dangerous?

We have no specific security note for port 3921. 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 3921

ServicePortTransportDescriptionReferenceUpdated
herodotus-net 3921 TCP, UDP Herodotus Net - 2003-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3921, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3921'      # process listening on 3921
sudo lsof -nP -i :3921

macOS

sudo lsof -nP -i :3921

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3921 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3921
netstat -ano | findstr :3921

From another machine

nmap -p 3921 -sV <host>
sudo nmap -sU -p 3921 <host>
nc -zv <host> 3921

Block it in the firewall

sudo ufw deny 3921/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3921" -Direction Inbound -LocalPort 3921 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3921 used for?

Port 3921 is assigned by IANA to herodotus-net (Herodotus Net).

Is port 3921 TCP or UDP?

Port 3921 is registered for TCP and UDP.

Is it safe to open port 3921?

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 3921 is open?

On Linux run "ss -ltnup 'sport = :3921'", on macOS "lsof -nP -i :3921", and on Windows "netstat -ano | findstr :3921" to see the local process. From another machine, "nmap -p 3921 <host>" shows whether it is reachable.

05 Related
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