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// Other services

Port 21221: Services for Air Server

Port 21221 is assigned by IANA to aigairserver (Services for Air Server).

21221

How aigairserver works

Other services
client:21221aigairserverresponse client:21221aigairserverresponse

The client sends a request to port 21221 and the aigairserver 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 21221 dangerous?

We have no specific security note for port 21221. 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 21221

ServicePortTransportDescriptionReferenceUpdated
aigairserver 21221 TCP Services for Air Server - 2017-03-16
-21221-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 21221, and is it reachable?

Linux

sudo ss -ltnup 'sport = :21221'      # process listening on 21221
sudo lsof -nP -i :21221

macOS

sudo lsof -nP -i :21221

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21221 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 21221
netstat -ano | findstr :21221

From another machine

nmap -p 21221 -sV <host>
nc -zv <host> 21221

Block it in the firewall

sudo ufw deny 21221/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 21221" -Direction Inbound -LocalPort 21221 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 21221 used for?

Port 21221 is assigned by IANA to aigairserver (Services for Air Server).

Is port 21221 TCP or UDP?

Port 21221 is registered for TCP.

Is it safe to open port 21221?

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 21221 is open?

On Linux run "ss -ltnup 'sport = :21221'", on macOS "lsof -nP -i :21221", and on Windows "netstat -ano | findstr :21221" to see the local process. From another machine, "nmap -p 21221 <host>" shows whether it is reachable.

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