Subnetting Problem Patterns and Techniques work

Subnetting Problem Patterns and Techniques work
by Romi Satria Wahono
At the time of teaching and comprehend the material in class networking subnetting or CCNA, I usually using the method as I wrote in two previous articles:
Understanding
1. Subnetting Concept
2. Count Subnetting

1. SubnetMask ASKED QUESTIONS BY THE TERMS OF THE NUMBER OF HOST OR SUBNET
Questions are asked Subnet what should be used to limit the number of hosts or subnets
determined in the matter. To answer this question we use the formula to calculate the number of hosts per subnet, ie 2y - 2, where y is the number of binary 0 in the last octet Subnet. And if determined is the number of subnets, we use the formula 2x (way after 2005) or 2x - 2 (means before 2005), where x is the number of binary 1 in the last octet Subnet.
Question: A company is planning to subnet its network for a maximum of 27 hosts. Which Subnet Would Provide the needed hosts and leave the fewest unused addresses in EACH subnet?
Answer: Because the requirement is 27 hosts, we just enter into the formula 2y - 2, where

the answer can not be less than (or equal to) 27. So 2y - 2> = 27, so the value of y right is 5 (30 hosts). Once again, because y is the number of binary 0 in the last octet

Subnet, so if we arrange subnetmasknya becomes 11111111.11111111.11111111.11100000
or if we desimalkan be 255,255,255,224. That is the answer
Problem: You have a Class B network ID and need about 450 IP addresses per subnet. What is the best mask for this network?
Answer: 2y - 2> = 450. The exact value of y is 9 (510 hosts). So subnetmasknya are:
11111111.11111111.11111110.00000000 or if didesimalkan be 255.255.254.0 (that is the answer!)

Question: Refer to the exhibit. The internetwork in the exhibit has been assigned the IP address 172.20.0.0. What would be the Appropriate subnet mask to maximize the number of networks available for future growth?
Answer: Find the number of hosts per subnet is greatest, make the referral because if we take the smallest existing probably needs a larger host not fulfilled. So for this matter 2y - 2> = 850. Y values The most appropriate is 10 (1022 host). So subnetmask is 11111111.11111111.11111100.00000000 or 255.255.252.0