Subnetting Quick Method Example 1

172.16.35.123/20

Concerned Octet = 3rd Mask = 255.255.240.0 (left to right) Subnet Block = 16 (right to left) (or) / (256-240=16)

172.16.0.0 (NID)

172.16.16.0 (NID)

172.16.32.0 (NID) (Concerned Octet)

172.16.32.1 (First Host Add in a Subnet)

. .

172.16.47.254 (Last Host Add in a Subnet)

172.16.47.255 (BID)

172.16.48.0 (NID)

Reference:

Cisco CCNA 200-301 Exam: Complete Course with practical labs | Udemy