CyberHunter
Local dataset, no network
// Other services

Port 21553: Raima RDM TFS

Port 21553 is assigned by IANA to rdm-tfs (Raima RDM TFS).

21553

How rdm-tfs works

Other services
client:21553rdm-tfsresponse client:21553rdm-tfsresponse

The client sends a request to port 21553 and the rdm-tfs service answers.

Transport
TCP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Other services
01 Security

Is port 21553 dangerous?

We have no specific security note for port 21553. 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 21553

ServicePortTransportDescriptionReferenceUpdated
rdm-tfs 21553 TCP Raima RDM TFS - 2011-05-02
-21553-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 21553, and is it reachable?

Linux

sudo ss -ltnup 'sport = :21553'      # process listening on 21553
sudo lsof -nP -i :21553

macOS

sudo lsof -nP -i :21553

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21553 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 21553
netstat -ano | findstr :21553

From another machine

nmap -p 21553 -sV <host>
nc -zv <host> 21553

Block it in the firewall

sudo ufw deny 21553/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 21553" -Direction Inbound -LocalPort 21553 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 21553 used for?

Port 21553 is assigned by IANA to rdm-tfs (Raima RDM TFS).

Is port 21553 TCP or UDP?

Port 21553 is registered for TCP.

Is it safe to open port 21553?

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 21553 is open?

On Linux run "ss -ltnup 'sport = :21553'", on macOS "lsof -nP -i :21553", and on Windows "netstat -ano | findstr :21553" to see the local process. From another machine, "nmap -p 21553 <host>" shows whether it is reachable.

05 Related
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