Finding all subnets 1

WE HAVE LESS THAN 8 SUBNET BITS

160.100.0.0 /19
255.255.224.0

 

We have:
Network bits = 16
Subnet bits = 3 (23 = 8 subnets)
Host bits = 13

 

Steps:

  1. Write subnet mask and Network number into the table
  2. Find interesting octet (octet where mask is not 0 or 225)
  3. SPECIAL = 32
  4. Copy uninteresting octets and always add SPECIAL into interesting octet

     

 

Finding all subnets 2

WE HAVE MORE THAN 8 SUBNET BITS

10.0.0.0 /18
255.255.192.0

We have:
Network bits = 8
Subnet bits = 10 (210 = 1024 subnets)
Host bits = 14

 

Steps:

  1. Write subnet mask and Network number into the table
  2. Find interesting octet (octet where mask is not 0 or 225)
  3. SPECIAL = 64
  4. Copy uninteresting octets and always add SPECIAL into interesting octet. If we have subnet 4 and we want to add SPECIAL, result is 256, instead 256 write 0 and add 1 to the octet to the left

 

 

Source:

CCENT/CCNA ICND1 Official Exam Certification Guide, Second Edition [Wendell Odom]