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// Directory & authentication

Port 3661: IBM Tivoli Directory Service using SSL

Port 3661 is assigned by IANA to can-ferret-ssl (IBM Tivoli Directory Service using SSL).

3661

How can-ferret-ssl works

Directory & authentication
userdirectorycan-ferret-sslresponse userdirectorycan-ferret-sslresponse

The client proves who it is on port 3661 and gets an answer (or a ticket) it can use with other services.

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
Directory & authentication
01 Security

Is port 3661 dangerous?

We have no specific security note for port 3661. Its risk depends on the program actually listening on it. General advice for directory & authentication services:

  • Keep directory and authentication services on internal networks.
  • Require signing or TLS and disable anonymous queries.
  • Monitor authentication failures for spraying and brute force.
02 Registry

IANA registry entries for port 3661

ServicePortTransportDescriptionReferenceUpdated
can-ferret-ssl 3661 TCP, UDP IBM Tivoli Directory Service using SSL - 2003-01

// source: IANA service name and port number registry

03 Check it

Which program uses port 3661, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3661'      # process listening on 3661
sudo lsof -nP -i :3661

macOS

sudo lsof -nP -i :3661

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3661 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3661
netstat -ano | findstr :3661

From another machine

nmap -p 3661 -sV <host>
sudo nmap -sU -p 3661 <host>
nc -zv <host> 3661

Block it in the firewall

sudo ufw deny 3661/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3661" -Direction Inbound -LocalPort 3661 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3661 used for?

Port 3661 is assigned by IANA to can-ferret-ssl (IBM Tivoli Directory Service using SSL).

Is port 3661 TCP or UDP?

Port 3661 is registered for TCP and UDP.

Is it safe to open port 3661?

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. Keep directory and authentication services on internal networks.

How do I check if port 3661 is open?

On Linux run "ss -ltnup 'sport = :3661'", on macOS "lsof -nP -i :3661", and on Windows "netstat -ano | findstr :3661" to see the local process. From another machine, "nmap -p 3661 <host>" shows whether it is reachable.

05 Related
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp

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