CyberHunter
Local dataset, no network
// Other services

Port 177: X Display Manager Control Protocol

Port 177 is assigned by IANA to xdmcp (X Display Manager Control Protocol).

177

How xdmcp works

Other services
client:177xdmcpresponse client:177xdmcpresponse

The client sends a request to port 177 and the xdmcp service answers.

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
Other services
01 Security

Is port 177 dangerous?

We have no specific security note for port 177. 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 177

ServicePortTransportDescriptionReferenceUpdated
xdmcp 177 TCP, UDP X Display Manager Control Protocol - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 177, and is it reachable?

Linux

sudo ss -ltnup 'sport = :177'      # process listening on 177
sudo lsof -nP -i :177

macOS

sudo lsof -nP -i :177

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 177 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 177
netstat -ano | findstr :177

From another machine

nmap -p 177 -sV <host>
sudo nmap -sU -p 177 <host>
nc -zv <host> 177

Block it in the firewall

sudo ufw deny 177/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 177" -Direction Inbound -LocalPort 177 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 177 used for?

Port 177 is assigned by IANA to xdmcp (X Display Manager Control Protocol).

Is port 177 TCP or UDP?

Port 177 is registered for TCP and UDP.

Is it safe to open port 177?

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 177 is open?

On Linux run "ss -ltnup 'sport = :177'", on macOS "lsof -nP -i :177", and on Windows "netstat -ano | findstr :177" to see the local process. From another machine, "nmap -p 177 <host>" shows whether it is reachable.

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