IP Addressing Scheme for National Retail Chain - Exam 200-125 | Cisco

# Designing IP Addressing Scheme for Nationwide Network

### Question

A national retail chain needs to design an IP addressing scheme to support a nationwide network.

The company needs a minimum of 300 sub-networks and a maximum of 50 host addresses per subnet.

Working with only one Class B address, which of the following subnet masks will support an appropriate addressing scheme? (Choose two.)

### Explanations

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A. B. C. D. E. F.

BE

50 hosts per subnet, so we'd need a range of 64 IP addresses which is a /26. This converts to a mask of 255.255.255.192.

To support a nationwide network with a minimum of 300 sub-networks and a maximum of 50 host addresses per subnet, we need to carefully select a subnet mask that meets these requirements.

We have been given a Class B address, which means the default subnet mask is 255.255.0.0. However, this would only allow for 16,384 hosts on the entire network, which is not sufficient for our requirements. Therefore, we need to use subnetting to create smaller sub-networks with fewer hosts.

We can calculate the number of host addresses per subnet based on the subnet mask. The formula for calculating the number of host addresses per subnet is:

2^(number of host bits) - 2

The "-2" accounts for the network address and the broadcast address, which cannot be assigned to hosts.

Now let's look at each of the given subnet masks and calculate the number of host addresses per subnet:

A. 255.255.255.0 = 2^8 - 2 = 254 (not sufficient for our requirements) B. 255.255.255.128 = 2^7 - 2 = 126 (meets our requirement for a maximum of 50 hosts, but we need more subnets than 300) C. 255.255.252.0 = 2^10 - 2 = 1022 (meets our requirement for a minimum of 300 subnets, but allows for too many hosts per subnet) D. 255.255.255.224 = 2^5 - 2 = 30 (not sufficient for our requirements) E. 255.255.255.192 = 2^6 - 2 = 62 (meets our requirement for a maximum of 50 hosts, but we need more subnets than 300) F. 255.255.248.0 = 2^13 - 2 = 8190 (allows for too many hosts per subnet)

Based on these calculations, options B and E are the best choices for our requirements. Option B (255.255.255.128) allows for a maximum of 126 hosts per subnet, which is sufficient for our requirement of a maximum of 50 hosts per subnet. Option E (255.255.255.192) allows for a maximum of 62 hosts per subnet, which is also sufficient for our requirement of a maximum of 50 hosts per subnet. However, since option B allows for fewer subnets than option E, we would likely choose option E as our subnet mask to meet the requirement of a minimum of 300 sub-networks.

Therefore, the two subnet masks that will support an appropriate addressing scheme for this network are B (255.255.255.128) and E (255.255.255.192).