code: function normalize(from, to) {
    if (from && (isNaN(from) || from <= 0) || (to && (isNaN(to) || to <= 0))) {
      throw new Error('invalid port range: required > 0');
    }
    if ((from && from > MAX) || (to && to > MAX)) {
      throw new Error(f('invalid port range: required < %d', MAX));
    }
    if (to && to < from) {
      throw new Error('invalid port range: required max >= min');
    }
    if (!from) {
      from = min;
      to = to || max;
    } else {
      to = to || from;
    }
    return {
      from: from,
      to: to
    };
  }
docs: Normalize a TCP ports range
  
  @param {Number} [from] Start port (included)
  @param {Number} [to] End port (included)
  @return {{from: {Number}, to: {Number}}}
  @private
  @ignore