Insertion Sort with a C++ vector and iterators

In order to practice my programming skills, I thought I'd write some basic sorting algorithms from scratch. Below is my code to do an insertion sort of a vector with iterators in C++.
This took me longer to write than I am willing to admit, indicating that I should continue practicing and writing these algorithms.

void insertion_sort( std::vector & v ) 
{
    // leave if there is nothing to sort
    if ( v.empty() )
    {
        return;
    }

    // go left to right along the vector
    std::vector::iterator l2r_it;
    l2r_it = v.begin();
    l2r_it++;
    for ( ; l2r_it != v.end(); l2r_it++ ) 
    {
        //  go right to left along the vector
        std::vector::iterator r2l_it = l2r_it ;
        while ( r2l_it != v.begin() &&
                *r2l_it < *(r2l_it - 1) )
        {
            int tmp = *r2l_it;
            *r2l_it = *(r2l_it - 1);
            *(r2l_it - 1 ) = tmp;

            r2l_it--;
        }
    }
}