def load_remote_peering_vlan_ids(d_fpaths_by_period):
    """
    Load VLAN ids which identify remote peering interconnections.
    """
    d_output = dict()

    for k_period, v_path in d_fpaths_by_period.iteritems():

        f = open(v_path)
        if k_period not in d_output:
            d_output[k_period] = set(map(int, f.read().strip().splitlines()))

    return d_output