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Difficulty: MediumIPv4 Addressing and Subnetting

A network engineer is provisioning host IP addresses within the enterprise subnet block 192.168.48.0/20192.168.48.0/20. Which of the following IP addresses are valid usable host addresses for endpoints on this subnetwork? (Select two.)

  1. 192.168.50.100192.168.50.100Answer
  2. 192.168.63.254192.168.63.254Answer
  3. C
    192.168.48.0192.168.48.0
  4. D
    192.168.63.255192.168.63.255

Answer

The addresses 192.168.50.100192.168.50.100 and 192.168.63.254192.168.63.254 are valid usable host addresses within the 192.168.48.0/20192.168.48.0/20 subnet.
For the prefix /20/20, the third octet increments in blocks of 16 (256−240=16256 - 240 = 16). For the subnet starting at 192.168.48.0192.168.48.0, the subnet range spans from 192.168.48.0192.168.48.0 to 192.168.63.255192.168.63.255. Subtracting the network ID (192.168.48.0192.168.48.0) and broadcast ID (192.168.63.255192.168.63.255) leaves a usable host range of 192.168.48.1192.168.48.1 through 192.168.63.254192.168.63.254. Therefore, 192.168.50.100192.168.50.100 and 192.168.63.254192.168.63.254 are valid host assignments.

Step-by-Step Solution

1
Determine the subnet mask block size for the /20 prefix length.
A /20/20 prefix corresponds to a subnet mask of 255.255.240.0255.255.240.0. The block size in the third octet is 256−240=16256 - 240 = 16.
Prefix length /20/20 uses 4 subnet bits in the third octet (128+64+32+16=240128 + 64 + 32 + 16 = 240).
2
Identify the network address and broadcast address boundaries.
Subnet Network ID: 192.168.48.0192.168.48.0. Next Subnet ID: 192.168.64.0192.168.64.0. Broadcast Address: 192.168.63.255192.168.63.255.
Adding the block size of 16 to the third octet start (48+1648 + 16) gives the next subnet boundary at 192.168.64.0192.168.64.0.
3
Calculate the usable host address range.
Usable host range: 192.168.48.1192.168.48.1 to 192.168.63.254192.168.63.254.
Usable hosts exclude the network ID (192.168.48.0192.168.48.0) and broadcast address (192.168.63.255192.168.63.255).
4
Evaluate the choices against the usable host address range.
192.168.50.100192.168.50.100 and 192.168.63.254192.168.63.254 fall within the usable range, whereas 192.168.48.0192.168.48.0 (network ID) and 192.168.63.255192.168.63.255 (broadcast ID) are reserved.
Only IP addresses between the first host and last host can be assigned to endpoint interfaces.

Key Concept

IPv4 Subnet Boundaries and Usable Host Range Calculation
Estimated Time:1m 30s
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Topics

IPv4 Addressing and Subnetting

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