The idea of ​​using an Arduino to send commands to a MikroTik device over Ethernet using Telnet is technically possible, but it has several considerations and limitations that you should keep in mind. Here I break down how you could try to do this, along with the complications and alternatives:

Technical viability

1. Arduino Capability:
   • Arduino models that have network connectivity capability (such as Arduino Ethernet, Arduino Uno with an Ethernet shield, or Arduino Yún) can be programmed to use network protocols such as Telnet.
   • You will need a Telnet library for Arduino, which allows you to establish and manage Telnet connections. Not all libraries will support all the features you might need.
2. Security and Telnet:
   • Telnet is not secure. Credentials and commands transmitted over Telnet are not encrypted, which exposes them to interception. Seriously consider the security implications, especially in a production environment.
3. MikroTik Configuration:
   • The MikroTik must be configured to allow management via Telnet. This involves enabling the Telnet service and ensuring that the firewall allows Telnet traffic to the device.
   • You will need to configure appropriate users and permissions on the MikroTik to allow user creation via Telnet commands.

Code Example for Arduino

Here is a basic outline of how you could structure the code in Arduino to send Telnet commands:

#include <Ethernet.h>
#include <TelnetClient.h>

// Configuración de la dirección IP del MikroTik y las credenciales
IPAddress server(192, 168, 1, 1); // IP del MikroTik
int telnetPort = 23;
char* username = "admin";
char* password = "password";

EthernetClient ethClient;
TelnetClient telnet(ethClient);

void setup() {
  Ethernet.begin(mac, ip);
  telnet.begin(server, telnetPort);
  
  if (telnet.login(username, password)) {
    telnet.println("/user add name=nuevoUsuario password=nuevaContraseña group=full");
  }
}

void loop() {
  // Aquí podrías agregar lógica para enviar comandos adicionales o manejar respuestas
}

Considerations

• Hardware Performance and Limitations: Arduino is limited in terms of memory and processing capacity, which could restrict the complexity and number of tasks it can handle.
• Safer Alternatives: Consider using SSH instead of Telnet if possible. SSH offers encryption and is widely supported, although it can be more challenging to implement on Arduino due to the greater protocol complexity and hardware requirements for encryption.

Conclusion

Although it is technically possible to configure an Arduino to send Telnet commands to a MikroTik, you must carefully consider security, reliability, and technical limitations. Evaluate whether a more robust and secure solution like a Raspberry Pi with SSH would be a better option for your needs.