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Difficulty: Very hardIPv4 Addressing and Subnetting

A network administrator is provisioning IPv4 subnets within the 10.50.0.0/1610.50.0.0/16 network block. A new department requires allocation for up to 500500 usable host interfaces. The administrator assigns the smallest matching single CIDR block starting at 10.50.0.0/2310.50.0.0/23. Which of the following IP addresses represent valid usable host addresses within this assigned subnet? (Select TWO.)

  1. 10.50.0.25510.50.0.255Answer
  2. 10.50.1.110.50.1.1Answer
  3. C
    10.50.1.25510.50.1.255
  4. D
    10.50.2.110.50.2.1

Answer

The valid usable host IP addresses within the 10.50.0.0/2310.50.0.0/23 subnet are 10.50.0.25510.50.0.255 and 10.50.1.110.50.1.1.
The assigned prefix /23/23 creates a subnet spanning 10.50.0.010.50.0.0 to 10.50.1.25510.50.1.255. Within this 512-address block, 10.50.0.010.50.0.0 is the network ID and 10.50.1.25510.50.1.255 is the broadcast address. The usable host range is 10.50.0.110.50.0.1 through 10.50.1.25410.50.1.254. Both 10.50.0.25510.50.0.255 and 10.50.1.110.50.1.1 fall within this valid host range.

Step-by-Step Solution

1
Determine the subnet block range for 10.50.0.0/2310.50.0.0/23
A /23/23 prefix provides 232−23=5122^{32-23} = 512 total IP addresses (256×2256 \times 2). The block starts at 10.50.0.010.50.0.0 and ends at 10.50.1.25510.50.1.255.
Calculating the total size establishes the exact boundary of the assigned network segment.
2
Identify network and broadcast addresses
Network ID = 10.50.0.010.50.0.0, Broadcast Address = 10.50.1.25510.50.1.255.
The first address in the block is reserved as the network identifier and the last address is reserved for subnet-wide broadcasts.
3
Calculate the usable host IP address range
Usable host range spans from 10.50.0.110.50.0.1 to 10.50.1.25410.50.1.254.
Usable addresses exclude the reserved network ID and broadcast address.
4
Evaluate candidate IP addresses against the usable range
10.50.0.25510.50.0.255 and 10.50.1.110.50.1.1 fall inside [10.50.0.1,10.50.1.254][10.50.0.1, 10.50.1.254], while 10.50.1.25510.50.1.255 is the broadcast address and 10.50.2.110.50.2.1 is in the next subnet.
Matching each address identifies which ones are valid for host assignment.

Key Concept

IPv4 CIDR Subnetting and Usable Host Boundaries
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Topics

IPv4 Addressing and Subnetting

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