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Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator is configuring static IP address assignments for high-availability database servers within an enterprise subnet designated as 172.20.48.0/28172.20.48.0/28. Which of the following IP addresses are valid usable host IP addresses that can be assigned to these servers? (Select TWO)

  1. 172.20.48.1Answer
  2. 172.20.48.14Answer
  3. C
    172.20.48.0
  4. D
    172.20.48.15
  5. E
    172.20.48.16

Answer

The valid usable host IP addresses within the 172.20.48.0/28 subnet are 172.20.48.1 and 172.20.48.14.
For the network block 172.20.48.0/28, a prefix length of /28 provides 16 total IP addresses (232−28=162^{32-28} = 16). The reserved network address is 172.20.48.0 and the reserved broadcast address is 172.20.48.15. The range of assignable host addresses is 172.20.48.1 through 172.20.48.14 inclusive. Therefore, 172.20.48.1 and 172.20.48.14 are valid usable host addresses.

Step-by-Step Solution

1
Determine the block size for a /28 subnet prefix.
A /28 prefix leaves 32−28=432 - 28 = 4 host bits. The total number of IP addresses per subnet is 24=162^4 = 16.
Calculating the total size of the subnet identifies the boundary conditions.
2
Identify the network ID and broadcast address for the subnet block.
The network address is 172.20.48.0. The broadcast address is 172.20.48.0+16−1=172.20.48.15172.20.48.0 + 16 - 1 = 172.20.48.15.
The network address is the first address in the block and the broadcast address is the last.
3
Determine the range of usable host IP addresses.
The usable host IP range spans from 172.20.48.1172.20.48.1 (network ID + 1) to 172.20.48.14172.20.48.14 (broadcast ID - 1).
Network and broadcast addresses are reserved and cannot be configured on individual host interfaces.
4
Evaluate the candidate options against the valid host range.
172.20.48.1 and 172.20.48.14 both fall within the usable range [172.20.48.1 - 172.20.48.14].
Only IP addresses strictly between the network ID and broadcast ID can be statically assigned to host devices.

Key Concept

IPv4 Host Range Determination
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Topics

IPv4 Addressing and Subnetting

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