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// Directory & authentication

Port 24321: Isolv Local Directory

Port 24321 is assigned by IANA to ild (Isolv Local Directory).

24321

How ild works

Directory & authentication
userdirectoryildresponse userdirectoryildresponse

The client proves who it is on port 24321 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 24321 dangerous?

We have no specific security note for port 24321. 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 24321

ServicePortTransportDescriptionReferenceUpdated
ild 24321 TCP, UDP Isolv Local Directory - 2005-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 24321, and is it reachable?

Linux

sudo ss -ltnup 'sport = :24321'      # process listening on 24321
sudo lsof -nP -i :24321

macOS

sudo lsof -nP -i :24321

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 24321 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 24321
netstat -ano | findstr :24321

From another machine

nmap -p 24321 -sV <host>
sudo nmap -sU -p 24321 <host>
nc -zv <host> 24321

Block it in the firewall

sudo ufw deny 24321/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 24321" -Direction Inbound -LocalPort 24321 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 24321 used for?

Port 24321 is assigned by IANA to ild (Isolv Local Directory).

Is port 24321 TCP or UDP?

Port 24321 is registered for TCP and UDP.

Is it safe to open port 24321?

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 24321 is open?

On Linux run "ss -ltnup 'sport = :24321'", on macOS "lsof -nP -i :24321", and on Windows "netstat -ano | findstr :24321" to see the local process. From another machine, "nmap -p 24321 <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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