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// Other services

Port 753:

Port 753 is assigned by IANA to rrh ().

753

How rrh works

Other services
client:753rrhresponse client:753rrhresponse

The client sends a request to port 753 and the rrh 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 753 dangerous?

We have no specific security note for port 753. 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 753

ServicePortTransportDescriptionReferenceUpdated
rrh 753 TCP, UDP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 753, and is it reachable?

Linux

sudo ss -ltnup 'sport = :753'      # process listening on 753
sudo lsof -nP -i :753

macOS

sudo lsof -nP -i :753

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 753 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 753
netstat -ano | findstr :753

From another machine

nmap -p 753 -sV <host>
sudo nmap -sU -p 753 <host>
nc -zv <host> 753

Block it in the firewall

sudo ufw deny 753/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 753" -Direction Inbound -LocalPort 753 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 753 used for?

Port 753 is assigned by IANA to rrh ().

Is port 753 TCP or UDP?

Port 753 is registered for TCP and UDP.

Is it safe to open port 753?

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 753 is open?

On Linux run "ss -ltnup 'sport = :753'", on macOS "lsof -nP -i :753", and on Windows "netstat -ano | findstr :753" to see the local process. From another machine, "nmap -p 753 <host>" shows whether it is reachable.

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