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Difficulty: EasyIPv4 Addressing and Subnetting

A network administrator is provisioning an IPv4 network segment for a branch office using the subnet mask 255.255.255.224255.255.255.224 (/2727). What is the maximum number of usable host IPv4 addresses that can be assigned to devices on this subnet?

  1. 30Answer
  2. B
    32
  3. C
    14
  4. D
    62

Answer

30 usable host IPv4 addresses
A subnet mask of 255.255.255.224255.255.255.224 corresponds to CIDR notation /2727. Subtracting 27 network bits from the 32 total bits in an IPv4 address leaves 5 host bits. The total number of IP addresses in this block is 25=322^5 = 32. Subtracting the network address and the broadcast address (32−232 - 2) results in 30 usable host IP addresses.

Step-by-Step Solution

1
Determine the number of host bits in the subnet.
5 host bits (32−27=532 - 27 = 5).
An IPv4 address contains 32 bits in total, and a /2727 prefix reserves 27 bits for the network portion.
2
Calculate the total number of available IP addresses.
25=322^5 = 32 total IP addresses.
The total address capacity is determined by 2n2^n, where nn is the number of host bits.
3
Subtract reserved addresses to find the usable host count.
32−2=3032 - 2 = 30 usable host addresses.
The first address (network ID) and the last address (broadcast address) cannot be assigned to individual hosts.

Key Concept

Calculating usable host IPv4 addresses using CIDR notation and subnet masks
Estimated Time:45s
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Topics

IPv4 Addressing and Subnetting

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