A chart for CIDR translations:
mask A B C # networks .0 /8 /16 /24 1 0 .128 /9 /17 /25 2 0-128 .192 /10 /18 /26 4 0-64-128-192 .224 /11 /19 /27 8 0-32-64-96-128-160-192-224 .240 /12 /20 /28 16 0-16-32-48-64-80-96-112-128-144-160-\ 176-192-208-224-240 .248 /13 /21 /29 32 0-8-16-24-32-40-48-56-64-72-80-88-\ 96-104-112-120-128-136-144-152-\ 152-160-168-176-184-192-299-208-\ 216-224-232-240-248 .252 /14 /22 /30 64 0-4-8-12-16-20-24-28-32-36-40-44-\ 48-52-56-60-64-72-76-80-84-88-92-\ 96-100-104-108-112-116-120-124-128-\ 132-136-140-144-148-152-156-160-164-\ 168-172-176-180-184-188-192-196-200-\ 204-208-216-220-224-228-232-236-240-\ 244-248-252 .254 /15 /23 N/A 128 .255 N/A N/A /32The ``mask'' number refers to the first number
!= 255A, B and C refer to the position of the ``mask'',
A = second octet B = third octet C = final octet# = number of networks difference from classful address;
netmask = 255.240.0.0 network = 10.16.0.0 (10.16/12) broadcast = 10.31.255.255