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// Other services

Port 3331: MCS Messaging

Port 3331 is assigned by IANA to mcs-messaging (MCS Messaging).

3331

How mcs-messaging works

Other services
client:3331mcs-messagingresponse client:3331mcs-messagingresponse

The client sends a request to port 3331 and the mcs-messaging 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 3331 dangerous?

We have no specific security note for port 3331. 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 3331

ServicePortTransportDescriptionReferenceUpdated
mcs-messaging 3331 TCP, UDP MCS Messaging - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 3331, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3331'      # process listening on 3331
sudo lsof -nP -i :3331

macOS

sudo lsof -nP -i :3331

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3331 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3331
netstat -ano | findstr :3331

From another machine

nmap -p 3331 -sV <host>
sudo nmap -sU -p 3331 <host>
nc -zv <host> 3331

Block it in the firewall

sudo ufw deny 3331/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3331" -Direction Inbound -LocalPort 3331 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3331 used for?

Port 3331 is assigned by IANA to mcs-messaging (MCS Messaging).

Is port 3331 TCP or UDP?

Port 3331 is registered for TCP and UDP.

Is it safe to open port 3331?

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 3331 is open?

On Linux run "ss -ltnup 'sport = :3331'", on macOS "lsof -nP -i :3331", and on Windows "netstat -ano | findstr :3331" to see the local process. From another machine, "nmap -p 3331 <host>" shows whether it is reachable.

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