CyberHunter
Local dataset, no network
// Other services

Port 421: Ariel 2

Port 421 is assigned by IANA to ariel2 (Ariel 2).

421

How ariel2 works

Other services
client:421ariel2response client:421ariel2response

The client sends a request to port 421 and the ariel2 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 421 dangerous?

We have no specific security note for port 421. 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 421

ServicePortTransportDescriptionReferenceUpdated
ariel2 421 TCP, UDP Ariel 2 - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 421, and is it reachable?

Linux

sudo ss -ltnup 'sport = :421'      # process listening on 421
sudo lsof -nP -i :421

macOS

sudo lsof -nP -i :421

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 421 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 421
netstat -ano | findstr :421

From another machine

nmap -p 421 -sV <host>
sudo nmap -sU -p 421 <host>
nc -zv <host> 421

Block it in the firewall

sudo ufw deny 421/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 421" -Direction Inbound -LocalPort 421 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 421 used for?

Port 421 is assigned by IANA to ariel2 (Ariel 2).

Is port 421 TCP or UDP?

Port 421 is registered for TCP and UDP.

Is it safe to open port 421?

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 421 is open?

On Linux run "ss -ltnup 'sport = :421'", on macOS "lsof -nP -i :421", and on Windows "netstat -ano | findstr :421" to see the local process. From another machine, "nmap -p 421 <host>" shows whether it is reachable.

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