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// Directory & authentication

Port 198: Directory Location Service Monitor

Port 198 is assigned by IANA to dls-mon (Directory Location Service Monitor).

198

How dls-mon works

Directory & authentication
userdirectorydls-monresponse userdirectorydls-monresponse

The client proves who it is on port 198 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
Well-known (0-1023)
Category
Directory & authentication
01 Security

Is port 198 dangerous?

We have no specific security note for port 198. 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 198

ServicePortTransportDescriptionReferenceUpdated
dls-mon 198 TCP, UDP Directory Location Service Monitor - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 198, and is it reachable?

Linux

sudo ss -ltnup 'sport = :198'      # process listening on 198
sudo lsof -nP -i :198

macOS

sudo lsof -nP -i :198

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 198 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 198
netstat -ano | findstr :198

From another machine

nmap -p 198 -sV <host>
sudo nmap -sU -p 198 <host>
nc -zv <host> 198

Block it in the firewall

sudo ufw deny 198/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 198" -Direction Inbound -LocalPort 198 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 198 used for?

Port 198 is assigned by IANA to dls-mon (Directory Location Service Monitor).

Is port 198 TCP or UDP?

Port 198 is registered for TCP and UDP.

Is it safe to open port 198?

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 198 is open?

On Linux run "ss -ltnup 'sport = :198'", on macOS "lsof -nP -i :198", and on Windows "netstat -ano | findstr :198" to see the local process. From another machine, "nmap -p 198 <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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