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// Directory & authentication

Port 197: Directory Location Service

Port 197 is assigned by IANA to dls (Directory Location Service).

197

How dls works

Directory & authentication
userdirectorydlsresponse userdirectorydlsresponse

The client proves who it is on port 197 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 197 dangerous?

We have no specific security note for port 197. 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 197

ServicePortTransportDescriptionReferenceUpdated
dls 197 TCP, UDP Directory Location Service - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 197, and is it reachable?

Linux

sudo ss -ltnup 'sport = :197'      # process listening on 197
sudo lsof -nP -i :197

macOS

sudo lsof -nP -i :197

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 197 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 197
netstat -ano | findstr :197

From another machine

nmap -p 197 -sV <host>
sudo nmap -sU -p 197 <host>
nc -zv <host> 197

Block it in the firewall

sudo ufw deny 197/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 197" -Direction Inbound -LocalPort 197 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 197 used for?

Port 197 is assigned by IANA to dls (Directory Location Service).

Is port 197 TCP or UDP?

Port 197 is registered for TCP and UDP.

Is it safe to open port 197?

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 197 is open?

On Linux run "ss -ltnup 'sport = :197'", on macOS "lsof -nP -i :197", and on Windows "netstat -ano | findstr :197" to see the local process. From another machine, "nmap -p 197 <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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