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// Other services

Port 653: RepCmd

Port 653 is assigned by IANA to repscmd (RepCmd).

653

How repscmd works

Other services
client:653repscmdresponse client:653repscmdresponse

The client sends a request to port 653 and the repscmd 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 653 dangerous?

We have no specific security note for port 653. 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 653

ServicePortTransportDescriptionReferenceUpdated
repscmd 653 TCP, UDP RepCmd - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 653, and is it reachable?

Linux

sudo ss -ltnup 'sport = :653'      # process listening on 653
sudo lsof -nP -i :653

macOS

sudo lsof -nP -i :653

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 653 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 653
netstat -ano | findstr :653

From another machine

nmap -p 653 -sV <host>
sudo nmap -sU -p 653 <host>
nc -zv <host> 653

Block it in the firewall

sudo ufw deny 653/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 653" -Direction Inbound -LocalPort 653 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 653 used for?

Port 653 is assigned by IANA to repscmd (RepCmd).

Is port 653 TCP or UDP?

Port 653 is registered for TCP and UDP.

Is it safe to open port 653?

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 653 is open?

On Linux run "ss -ltnup 'sport = :653'", on macOS "lsof -nP -i :653", and on Windows "netstat -ano | findstr :653" to see the local process. From another machine, "nmap -p 653 <host>" shows whether it is reachable.

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