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Cisco™ CCNA : Subnetting
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Subnetting Scenario Question 1
You want X number of subnets, what is the subnet mask ? (Assume we need 10 subnets, i.e, X=10)
Tip : Convert X to binary, determine how many low order bits need to make the number, that many bits is number of high order bits that make up your subnet mask, convert high order bits to
decimal value.
Solution :
Consider the Class C address – N.N.N.H where N is the Network portion and H is the host portion. Host Portion is as shown ----->
Step 1: Convert 10 to binary. Binary equivalent of 10 is as shown --------->
Step 2: Number of low order bits required to make the number is 4 (from the figure shown above)
Step 3: Therefore 4 high-order bits make up the subnet mask, i.e, 128, 64, 32, 16
Add 4 high order bits to create subnet mask i.e. 128+64+32+16=240 (11110000). The subnet mask is 255.255.255.255.240
255.255.255.240 is represented as -------->
Requirement for IPv4 Subnetting
1. Efficient use of available IP address space
2. Network traffic isolation
3. Improved security
4. Limiting broadcast messages
Subnetting Scenarios
The subnetting scenarios may broadly be divided in to two categories:
1. Optimize for a given number of hosts
2. Optimize for a given number of subnets
Finally, determine the host address range for each available subnet.