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Difficulty: MediumIPv4 Addressing and Subnetting

A network engineer is manually assigning static IPv4 addresses to industrial control gateways within an automated manufacturing segment using the address block 172.20.64.0/22172.20.64.0/22. Which of the following IPv4 addresses are valid, usable host addresses that can be assigned to devices on this subnet? (Select TWO.)

  1. 172.20.64.1172.20.64.1Answer
  2. 172.20.67.254172.20.67.254Answer
  3. C
    172.20.64.0172.20.64.0
  4. D
    172.20.67.255172.20.67.255
  5. E
    172.20.68.1172.20.68.1

Answer

The addresses 172.20.64.1172.20.64.1 and 172.20.67.254172.20.67.254 are valid, usable host IP addresses within the 172.20.64.0/22172.20.64.0/22 subnet.
The subnet 172.20.64.0/22172.20.64.0/22 covers the IP range 172.20.64.0172.20.64.0 through 172.20.67.255172.20.67.255. Subtracting the network address (172.20.64.0172.20.64.0) and the broadcast address (172.20.67.255172.20.67.255) yields a usable host IP address range of 172.20.64.1172.20.64.1 to 172.20.67.254172.20.67.254. Both 172.20.64.1172.20.64.1 and 172.20.67.254172.20.67.254 fall inside this range.

Step-by-Step Solution

1
Determine the subnet mask and block size for a /22/22 prefix length.
A /22/22 prefix corresponds to a subnet mask of 255.255.252.0255.255.252.0. The block size in the third octet is 256−252=4256 - 252 = 4.
Calculating the block size identifies the boundary increments between adjacent networks.
2
Identify the network ID and broadcast address for the 172.20.64.0/22172.20.64.0/22 network.
The network ID is 172.20.64.0172.20.64.0. The next subnet begins at 172.20.68.0172.20.68.0, making the broadcast address 172.20.67.255172.20.67.255.
Network addresses and broadcast addresses are reserved and cannot be assigned as usable host IPs.
3
Determine the valid host address range.
The usable host range spans from 172.20.64.1172.20.64.1 (first host) to 172.20.67.254172.20.67.254 (last host).
Usable host addresses consist of all IP addresses strictly between the network ID and the broadcast address.
4
Evaluate the choices against the usable host range.
172.20.64.1172.20.64.1 and 172.20.67.254172.20.67.254 lie within the usable range, whereas 172.20.64.0172.20.64.0 is the network ID, 172.20.67.255172.20.67.255 is the broadcast address, and 172.20.68.1172.20.68.1 belongs to another network.
Only IP addresses inside the calculated host range are valid host static assignments.

Key Concept

Usable IPv4 Host Range Calculation for Subnets Larger than /24/24
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Topics

IPv4 Addressing and Subnetting

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