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Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator is configuring a management server in an infrastructure VLAN. The default gateway interface for this subnet is assigned the IPv4 address 192.168.4.129192.168.4.129 with a subnet mask of 255.255.255.192255.255.255.192. Which of the following IPv4 addresses is a valid usable host address that can be assigned to the new server on this subnet?

  1. 192.168.4.150Answer
  2. B
    192.168.4.128
  3. C
    192.168.4.191
  4. D
    192.168.4.192

Answer

192.168.4.150 is the correct choice as it resides within the valid usable host range of the subnet.
The subnet mask 255.255.255.192255.255.255.192 (/26) creates subnets of 64 addresses each. The gateway IP 192.168.4.129192.168.4.129 belongs to the 192.168.4.128/26192.168.4.128/26 subnet, which has a network address of 192.168.4.128192.168.4.128, a broadcast address of 192.168.4.191192.168.4.191, and a usable host address range of 192.168.4.129192.168.4.129 through 192.168.4.190192.168.4.190. The address 192.168.4.150192.168.4.150 falls squarely within this usable host range.

Step-by-Step Solution

1
Determine the block size from the subnet mask.
A mask of 255.255.255.192255.255.255.192 corresponds to a /26/26 prefix length. The block size is 256−192=64256 - 192 = 64.
Knowing the block size allows identification of subnet boundaries.
2
Identify the network address containing the default gateway IP 192.168.4.129192.168.4.129.
Subnet blocks increment by 6464: .0.0, .64.64, .128.128, .192.192. The gateway address 192.168.4.129192.168.4.129 falls into the 192.168.4.128/26192.168.4.128/26 subnet.
The network address defines the lower bound of the subnet boundary.
3
Calculate the broadcast address and usable host range.
The broadcast address is 192.168.4.191192.168.4.191 (one less than the next subnet 192.168.4.192192.168.4.192). The usable host range spans from 192.168.4.129192.168.4.129 to 192.168.4.190192.168.4.190.
Usable host addresses exclude the network ID and broadcast address.
4
Evaluate the options against the usable host range.
192.168.4.150192.168.4.150 is the only option that falls within 192.168.4.129192.168.4.129 – 192.168.4.190192.168.4.190.
Host IP addresses must be strictly within the calculated usable range.

Key Concept

IPv4 Subnet Boundaries and Usable Host Allocation
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Topics

IPv4 Addressing and Subnetting

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