Running cat 6 networking cable in the attic: what is up to code?
Since you are in a one-family dwelling, there is really only one important article to be aware of.


  800.26 Spread of Fire or Products of Combustion. Installations of communications cables and communications raceways in hollow spaces,
  vertical shafts, and ventilation or air-handling ducts shall be made
  so that the possible spread of fire or products of combustion will not
  be substantially increased. Openings around penetrations of
  communications cables and communications raceways through
  fire-resistant-rated walls, partitions, floors, or ceilings shall be
  firestopped using approved methods to maintain the fire resistance
  rating.
  
  FPN: Directories of electrical construction materials published by qualified testing laboratories contain many listing installation
  restrictions necessary to maintain the fireresistive rating of
  assemblies where penetrations or openings are made. Building codes
  also contain restrictions on membrane penetrations on opposite sides
  of a fire resistance–rated wall assembly. An example is the 600 mm (24
  in.) minimum horizontal separation that usually applies between boxes
  installed on opposite sides of the wall. Assistance in complying with
  800.26 can be found in building codes, fire resistance directories, and product listings.


In a one- or two-family dwelling, you can use general type cable (CM, CMG, CMX) anywhere other than where plenum cable is required.


  800.154(B)(3) One- and Two-Family Dwellings. Type CM and CMX cable shall be permitted in one- and two-family dwellings.


Or, under carpets.


  800.154(C)(6) Under Carpets. Type CMUC undercarpet communications wires and cables shall be permitted to be installed under carpet.