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// Other services

Port 256: RAP

Port 256 is assigned by IANA to rap (RAP).

256

How rap works

Other services
client:256rapresponse client:256rapresponse

The client sends a request to port 256 and the rap 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 256 dangerous?

We have no specific security note for port 256. 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 256

ServicePortTransportDescriptionReferenceUpdated
rap 256 TCP, UDP RAP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 256, and is it reachable?

Linux

sudo ss -ltnup 'sport = :256'      # process listening on 256
sudo lsof -nP -i :256

macOS

sudo lsof -nP -i :256

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 256 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 256
netstat -ano | findstr :256

From another machine

nmap -p 256 -sV <host>
sudo nmap -sU -p 256 <host>
nc -zv <host> 256

Block it in the firewall

sudo ufw deny 256/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 256" -Direction Inbound -LocalPort 256 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 256 used for?

Port 256 is assigned by IANA to rap (RAP).

Is port 256 TCP or UDP?

Port 256 is registered for TCP and UDP.

Is it safe to open port 256?

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 256 is open?

On Linux run "ss -ltnup 'sport = :256'", on macOS "lsof -nP -i :256", and on Windows "netstat -ano | findstr :256" to see the local process. From another machine, "nmap -p 256 <host>" shows whether it is reachable.

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