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// Other services

Port 3873: fagordnc

Port 3873 is assigned by IANA to fagordnc (fagordnc).

3873

How fagordnc works

Other services
client:3873fagordncresponse client:3873fagordncresponse

The client sends a request to port 3873 and the fagordnc 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 3873 dangerous?

We have no specific security note for port 3873. 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 3873

ServicePortTransportDescriptionReferenceUpdated
fagordnc 3873 TCP, UDP fagordnc - 2003-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3873, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3873'      # process listening on 3873
sudo lsof -nP -i :3873

macOS

sudo lsof -nP -i :3873

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3873 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3873
netstat -ano | findstr :3873

From another machine

nmap -p 3873 -sV <host>
sudo nmap -sU -p 3873 <host>
nc -zv <host> 3873

Block it in the firewall

sudo ufw deny 3873/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3873" -Direction Inbound -LocalPort 3873 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3873 used for?

Port 3873 is assigned by IANA to fagordnc (fagordnc).

Is port 3873 TCP or UDP?

Port 3873 is registered for TCP and UDP.

Is it safe to open port 3873?

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 3873 is open?

On Linux run "ss -ltnup 'sport = :3873'", on macOS "lsof -nP -i :3873", and on Windows "netstat -ano | findstr :3873" to see the local process. From another machine, "nmap -p 3873 <host>" shows whether it is reachable.

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