(2) Where the principal is liable to pay compensation under this section, he shall be entitled to be indemnified by the contractor, 2[ or any other person from whom the workman could have recovered compensation and where a contractor who is himself a principal is liable to pay compensation or to indemnify a principal under this section he shall be entitled to be indemnified by any person standing to him in the relation of a contractor from whom the workman could have recovered compensation,] and all questions as to the right to and the amount of any such indemnity shall, in default of agreement, be settled by the Commissioner.