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// Other services

Port 3666: IBM eServer PAP

Port 3666 is assigned by IANA to eserver-pap (IBM eServer PAP).

3666

How eserver-pap works

Other services
client:3666eserver-papresponse client:3666eserver-papresponse

The client sends a request to port 3666 and the eserver-pap 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 3666 dangerous?

We have no specific security note for port 3666. 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 3666

ServicePortTransportDescriptionReferenceUpdated
eserver-pap 3666 TCP, UDP IBM eServer PAP - 2003-01

// source: IANA service name and port number registry

03 Check it

Which program uses port 3666, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3666'      # process listening on 3666
sudo lsof -nP -i :3666

macOS

sudo lsof -nP -i :3666

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3666 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3666
netstat -ano | findstr :3666

From another machine

nmap -p 3666 -sV <host>
sudo nmap -sU -p 3666 <host>
nc -zv <host> 3666

Block it in the firewall

sudo ufw deny 3666/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3666" -Direction Inbound -LocalPort 3666 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3666 used for?

Port 3666 is assigned by IANA to eserver-pap (IBM eServer PAP).

Is port 3666 TCP or UDP?

Port 3666 is registered for TCP and UDP.

Is it safe to open port 3666?

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 3666 is open?

On Linux run "ss -ltnup 'sport = :3666'", on macOS "lsof -nP -i :3666", and on Windows "netstat -ano | findstr :3666" to see the local process. From another machine, "nmap -p 3666 <host>" shows whether it is reachable.

05 Related
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