C++ Call by reference

If I have a function which takes a pointer to an integer, and I pass a reference to an integer variable from my main, is this call by value or call by reference? Sample code:

#include <iostream>

using namespace std;

void fun(int *a){
//Code block
}

int main(){
    int a = 5;
    fun(&a);
    return 0;
}

In the above code, is the call to function fun a call by value or call by reference?