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// Other services

Port 3431: Active License Server Port

Port 3431 is assigned by IANA to ndl-als (Active License Server Port).

3431

How ndl-als works

Other services
client:3431ndl-alsresponse client:3431ndl-alsresponse

The client sends a request to port 3431 and the ndl-als 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 3431 dangerous?

We have no specific security note for port 3431. 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 3431

ServicePortTransportDescriptionReferenceUpdated
ndl-als 3431 TCP, UDP Active License Server Port - 2002-03

// source: IANA service name and port number registry

03 Check it

Which program uses port 3431, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3431'      # process listening on 3431
sudo lsof -nP -i :3431

macOS

sudo lsof -nP -i :3431

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3431 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3431
netstat -ano | findstr :3431

From another machine

nmap -p 3431 -sV <host>
sudo nmap -sU -p 3431 <host>
nc -zv <host> 3431

Block it in the firewall

sudo ufw deny 3431/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3431" -Direction Inbound -LocalPort 3431 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3431 used for?

Port 3431 is assigned by IANA to ndl-als (Active License Server Port).

Is port 3431 TCP or UDP?

Port 3431 is registered for TCP and UDP.

Is it safe to open port 3431?

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 3431 is open?

On Linux run "ss -ltnup 'sport = :3431'", on macOS "lsof -nP -i :3431", and on Windows "netstat -ano | findstr :3431" to see the local process. From another machine, "nmap -p 3431 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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