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Question

Difficulty: EasyIPv4 Addressing and Subnetting

An administrator is configuring a switch management VLAN interface with an IPv4 address of 172.16.5.33 and a subnet mask of 255.255.255.224 (/27). What is the total number of usable host IP addresses available on this subnet?

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

Answer

The total number of usable host IP addresses available on a /27 subnet is 30.
The correct answer is 30. For a prefix of /27 (subnet mask 255.255.255.224), there are 32−27=532 - 27 = 5 host bits available. The total address block size is 25=322^5 = 32. Subtracting the network identifier and the broadcast address (32−232 - 2) gives exactly 30 usable host IP addresses.

Step-by-Step Solution

1
Determine the number of host bits from the prefix length.
32 total IPv4 address bits - 27 network bits = 5 host bits (n=5n = 5).
The prefix length /27 defines 27 bits for the network portion, leaving the remaining bits for host addressing.
2
Calculate the total number of IP addresses in the subnet block.
25=322^5 = 32 total IP addresses.
The formula 2n2^n calculates the total number of binary combinations available with nn host bits.
3
Subtract the non-assignable network and broadcast addresses to find the usable host count.
32−2=3032 - 2 = 30 usable host IP addresses.
In standard IPv4 subnetting, the first address (network ID) and last address (directed broadcast address) cannot be assigned to individual hosts.

Key Concept

Calculating Usable IPv4 Host Addresses using the 2n−22^n - 2 Formula
Estimated Time:45s
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Topics

IPv4 Addressing and Subnetting

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