Exam 200-310 topic 2 question 168 discussion

Your company is opening a branch office that will contain 29 host computers. Your company has been allocated the 192.168.10.0/24 address range, and you have been asked to conserve IP address space when creating a subnet for the new branch office.
Which of the following network addresses should you use for the new branch office? (

Suggested Answer: D 🗳️
Section: Addressing and Routing Protocols in an Existing Network Explanation

You should use the 192.168.10.64/27 network address for the new branch office. The /27 notation indicates that 27 bits are used for the network portion of the address and that five bits remain for the host portion of the address, which allows for 32 (25) usable host addresses. Therefore, this address range is large enough to handle the number of hosts on the new branch office subnet. The first address is the network address, the last address is the broadcast address, and the other
30 (25-2) addresses are usable host addresses. Therefore, this address range is large enough to handle a subnet containing 29 host computers.
You should always begin allocating address ranges starting with the largest group of hosts to ensure that the entire group has a large, contiguous address range available. Subnetting a contiguous address range in structured, hierarchical fashion enables routers to maintain smaller routing tables and eases administrative burden when troubleshooting.
You should not use the 192.168.10.0/25 network address for the new branch office. The /25 notation indicates that 25 bits are used for the network portion of the address and that 7 bits remain for the host portion of the address, which allows for 126 (27-2) usable host addresses. Although this address range is large enough to handle the new branch office subnet, it does not conserve IP address space, because a smaller range can successfully be used.
You should not use the 192.168.10.32/26 network address for the new branch office. Although a 26bit mask is large enough for 62 usable host addresses, the
192.168.10.32 address is not a valid network address for a 26-bit mask. The 192.168.10.0/24 address range can be divided into four ranges, each with 64 addresses, by using a 26-bit mask:
192.168.10.0/26
192.168.10.64/26
192.168.10.128/26
192.168.10.192/26
You should not use the 192.168.10.64/26 network address for the new branch office. The /26 notation indicates that 26 bits are used for the network portion of the address and that six bits remain for the host portion of the address, which allows for 62 (26-2) host addresses. Although this address range is large enough to handle the new branch office subnet, it does not conserve IP address space, because a smaller range can successfully be used.
Although it is important to learn the formula for calculating valid host addresses, the following list demonstrates the relationship between common subnet masks and valid host addresses:

Reference:
Cisco: IP Addressing and Subnetting for New Users