C ++ check at runtime if an object implements an interface

I asked this question a while ago: Multiple inheritance of inheritance from a base class to another derived class

But I'm still not sure I understand the answer. Question: Is the code below valid?

#include <iostream>

using namespace std;

struct Base
{
    virtual void printName() 
    {
        cout << "Base" << endl;
    }
};

struct Interface
{
    virtual void foo()
    {
        cout << "Foo function" << endl;
    }
};

struct Derived : public Base, public Interface
{
    virtual void printName()
    {
        cout << "Derived" << endl;
    }
};

int main(int argc, const char * argv[])
{
    Base *b = new Derived();
    Interface *i = dynamic_cast<Interface*>(b);
    i->foo();

    return 0;
}

The code works the way I want. But, as I understand it, according to the previous question, this should not. Therefore, I'm not sure if such code is valid. Thank!