How to control a router via telnet?

Question

network hardware

In general, why telnet on routers?
I have a dir-615 (d-link) router.
So I went to it via telnet, pinged, looked at the directories, and that's it.
And actually, what is telnet for? Can I install my own software on the router through it? how to find out through telnet what kind of axis is on it? linux? How to write your own for him? in what language? how to upload here?

Answer 1

Using telnet, you can usually do the same thing as using the web interface - setting up routing, networks, and other things.
Since you can telnet to directories, your router has an operating system. Possibly based on linux. Or maybe on some RTOS.
If you want your own software and more customization - install firmware on the OpenWRT router, if possible. Modules for OpenWRT are written in C or C++, like most similar low-level software. You should compile for the architecture of the processor installed in the router. Modules can be installed from a USB flash drive. Of the restrictions - the amount of ROM of the router. My dlink dir-620 had only 8 MB of space, OpenWRT itself took up 7 MB, little fit. I switched to the Asus firmware from the padawan, there is also a built-in torrent client.
You can also write your own firmware, again, see the source codes of OpenWRT or Padawan firmware. But the order of complexity is different.

Answer 2

/* test.c */
#include <stdio.h>

int main() {
    printf("Hello World\n");
    return 0;
}

gcc:
toolchains/bin/mips-linux-gcc test.c -o test.out -static
device:
cp /bin/cp /tmp/test.out
nc -lp 55555 > /tmp/test.out
host:
nc -q 1 192.168.0.1 55555 < test.out
device:
/tmp/test.out