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// Other services

Port 3942: satellite distribution

Port 3942 is assigned by IANA to srdp (satellite distribution).

3942

How srdp works

Other services
client:3942srdpresponse client:3942srdpresponse

The client sends a request to port 3942 and the srdp 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 3942 dangerous?

We have no specific security note for port 3942. 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 3942

ServicePortTransportDescriptionReferenceUpdated
srdp 3942 TCP, UDP satellite distribution - 2003-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 3942, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3942'      # process listening on 3942
sudo lsof -nP -i :3942

macOS

sudo lsof -nP -i :3942

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3942 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3942
netstat -ano | findstr :3942

From another machine

nmap -p 3942 -sV <host>
sudo nmap -sU -p 3942 <host>
nc -zv <host> 3942

Block it in the firewall

sudo ufw deny 3942/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3942" -Direction Inbound -LocalPort 3942 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3942 used for?

Port 3942 is assigned by IANA to srdp (satellite distribution).

Is port 3942 TCP or UDP?

Port 3942 is registered for TCP and UDP.

Is it safe to open port 3942?

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 3942 is open?

On Linux run "ss -ltnup 'sport = :3942'", on macOS "lsof -nP -i :3942", and on Windows "netstat -ano | findstr :3942" to see the local process. From another machine, "nmap -p 3942 <host>" shows whether it is reachable.

05 Related
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