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Difficulty: HardIPv4 Addressing and Subnetting

A network engineer is provisioning subnets for an enterprise database cluster within the allocated block 172.22.140.0/22172.22.140.0/22. The designated subnet for this VLAN is 172.22.142.128/25172.22.142.128/25. Which of the following IPv4 addresses represent valid usable host addresses that can be statically assigned to database interfaces in this subnet? (Select ALL that apply.)

  1. A
    172.22.142.128172.22.142.128
  2. 172.22.142.129172.22.142.129Answer
  3. 172.22.142.200172.22.142.200Answer
  4. D
    172.22.142.255172.22.142.255

Answer

The valid usable host IPv4 addresses for the subnet are 172.22.142.129172.22.142.129 and 172.22.142.200172.22.142.200.
For the subnet 172.22.142.128/25172.22.142.128/25, the prefix length /25/25 provides 128 total IP addresses (232−25=1282^{32-25} = 128). The network address is 172.22.142.128172.22.142.128 and the broadcast address is 172.22.142.255172.22.142.255. Consequently, the valid usable host IPv4 address range extends from 172.22.142.129172.22.142.129 up through 172.22.142.254172.22.142.254. Both 172.22.142.129172.22.142.129 and 172.22.142.200172.22.142.200 lie within this valid host range.

Step-by-Step Solution

1
Determine the prefix length and total block size.
A /25/25 prefix length leaves 32−25=732 - 25 = 7 host bits, yielding 27=1282^7 = 128 total IP addresses per subnet.
Understanding prefix length establishes the block boundary size.
2
Identify the network ID and broadcast address for 172.22.142.128/25172.22.142.128/25.
Network ID = 172.22.142.128172.22.142.128; Directed Broadcast Address = 172.22.142.128+127=172.22.142.255172.22.142.128 + 127 = 172.22.142.255.
The network address is the starting boundary and the broadcast address is the ending boundary.
3
Calculate the usable host IP address range.
Usable host range spans from 172.22.142.129172.22.142.129 (Network ID + 1) to 172.22.142.254172.22.142.254 (Broadcast Address - 1).
Network and broadcast addresses must be excluded when reserving addresses for host interfaces.
4
Evaluate the candidate options against the usable host range.
172.22.142.129172.22.142.129 and 172.22.142.200172.22.142.200 fall strictly within the usable host range, while 172.22.142.128172.22.142.128 (Network ID) and 172.22.142.255172.22.142.255 (Broadcast) do not.
Only IP addresses strictly within the usable host range are assignable to hosts.

Key Concept

IPv4 Subnet Boundaries and Usable Host Allocation
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Topics

IPv4 Addressing and Subnetting

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