Question

This is my function:

IEnumerable<Packet> packets = splitPacket(packet, 2);

public static IEnumerable<Packet> splitPacket(Packet packet, int numberOfFragments)
{
    //
}

I am calling this function but for some reason my code did not get into my function.

Answer 1

My psychic debugging skills tell me that your function is an iterator function, meaning that it contains yield return; statements.

Code in iterator functions is only executed as the result is iterated.
This is called deferred execution.