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Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator partitions the IPv4 block 192.168.50.0/24192.168.50.0/24 into subnets with a /27/27 prefix length. Which of the following IP addresses represent valid usable host addresses within the third subnet block? (Select TWO.)

  1. A
    192.168.50.64192.168.50.64
  2. 192.168.50.67192.168.50.67Answer
  3. 192.168.50.90192.168.50.90Answer
  4. D
    192.168.50.95192.168.50.95

Answer

The valid usable host addresses for the third /27/27 subnet are 192.168.50.67192.168.50.67 and 192.168.50.90192.168.50.90.
For the allocated block 192.168.50.0/24192.168.50.0/24, partitioning with a /27/27 subnet mask creates blocks of 32 IP addresses. The third subnet spans from 192.168.50.64192.168.50.64 to 192.168.50.95192.168.50.95. Subtracting the network ID (192.168.50.64192.168.50.64) and broadcast address (192.168.50.95192.168.50.95) yields the valid host IP range 192.168.50.65192.168.50.65 through 192.168.50.94192.168.50.94. Therefore, 192.168.50.67192.168.50.67 and 192.168.50.90192.168.50.90 are correct valid host IP assignments.

Step-by-Step Solution

1
Determine the block size for a /27/27 subnet mask.
A /27/27 mask gives 32−27=532 - 27 = 5 host bits. Block size =25=32= 2^5 = 32 addresses.
Calculating block size establishes the boundary boundaries for consecutive subnets.
2
Calculate network ranges for the first three subnets starting from 192.168.50.0192.168.50.0.
Subnet 1: 192.168.50.0−192.168.50.31192.168.50.0 - 192.168.50.31, Subnet 2: 192.168.50.32−192.168.50.63192.168.50.32 - 192.168.50.63, Subnet 3: 192.168.50.64−192.168.50.95192.168.50.64 - 192.168.50.95.
Identifying the third subnet boundaries isolates the specific address range being evaluated.
3
Determine the usable host IP address range for the third subnet.
Network ID: 192.168.50.64192.168.50.64, Broadcast Address: 192.168.50.95192.168.50.95, Usable Range: 192.168.50.65192.168.50.65 to 192.168.50.94192.168.50.94.
Usable host addresses exclude the first address (Network ID) and last address (Broadcast) of the block.
4
Compare given choices against the usable host IP address range.
192.168.50.67192.168.50.67 and 192.168.50.90192.168.50.90 fall within 192.168.50.65−192.168.50.94192.168.50.65 - 192.168.50.94, whereas 192.168.50.64192.168.50.64 and 192.168.50.95192.168.50.95 are network/broadcast addresses.
Confirms which addresses can actually be statically assigned to network host interfaces.

Key Concept

IPv4 Subnet Boundaries & Usable Host Ranges
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Topics

IPv4 Addressing and Subnetting

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