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// Other services

Port 172: Network Innovations CL/1 IANA assigned this well-formed service name as a replacement for "cl/1".

Port 172 is assigned by IANA to cl-1 (Network Innovations CL/1 IANA assigned this well-formed service name as a replacement for "cl/1".), cl/1 (Network Innovations CL/1).

172

How cl-1 works

Other services
client:172cl-1response client:172cl-1response

The client sends a request to port 172 and the cl-1 service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned2 registered services
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 172 dangerous?

We have no specific security note for port 172. 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 172

ServicePortTransportDescriptionReferenceUpdated
cl-1 172 TCP, UDP Network Innovations CL/1 IANA assigned this well-formed service name as a replacement for "cl/1". - -
cl/1 172 TCP, UDP Network Innovations CL/1 - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 172, and is it reachable?

Linux

sudo ss -ltnup 'sport = :172'      # process listening on 172
sudo lsof -nP -i :172

macOS

sudo lsof -nP -i :172

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 172 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 172
netstat -ano | findstr :172

From another machine

nmap -p 172 -sV <host>
sudo nmap -sU -p 172 <host>
nc -zv <host> 172

Block it in the firewall

sudo ufw deny 172/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 172" -Direction Inbound -LocalPort 172 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 172 used for?

Port 172 is assigned by IANA to cl-1 (Network Innovations CL/1 IANA assigned this well-formed service name as a replacement for "cl/1".), cl/1 (Network Innovations CL/1).

Is port 172 TCP or UDP?

Port 172 is registered for TCP and UDP.

Is it safe to open port 172?

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 172 is open?

On Linux run "ss -ltnup 'sport = :172'", on macOS "lsof -nP -i :172", and on Windows "netstat -ano | findstr :172" to see the local process. From another machine, "nmap -p 172 <host>" shows whether it is reachable.

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