Examkin

Question

Difficulty: Very hardIPv4 Addressing and Subnetting

A network administrator is implementing a Variable Length Subnet Masking (VLSM) plan for a company using the parent address space 172.16.32.0/20172.16.32.0/20. Subnets are allocated sequentially starting from the lowest available network address. First, the Engineering department is allocated a subnet accommodating at least 100100 usable host interfaces. Immediately following the Engineering subnet, the Sales department is allocated a subnet to accommodate at least 2828 usable host interfaces. Which of the following IPv4 addresses represent valid, usable host IP addresses within the Sales department subnet? (Select TWO.)

  1. 172.16.32.130172.16.32.130Answer
  2. B
    172.16.32.128172.16.32.128
  3. 172.16.32.158172.16.32.158Answer
  4. D
    172.16.32.159172.16.32.159
  5. E
    172.16.32.126172.16.32.126

Answer

The addresses 172.16.32.130172.16.32.130 and 172.16.32.158172.16.32.158 are the valid usable host IP addresses within the Sales department subnet.
The Sales department requires a subnet for at least 2828 host interfaces. A /27/27 subnet provides 3232 total addresses (3030 usable hosts). Since the Engineering department uses 172.16.32.0/25172.16.32.0/25 (address range 172.16.32.0172.16.32.0 - 172.16.32.127172.16.32.127), the Sales subnet begins at 172.16.32.128/27172.16.32.128/27. Its network address is 172.16.32.128172.16.32.128, its broadcast address is 172.16.32.159172.16.32.159, and its usable host range spans 172.16.32.129172.16.32.129 through 172.16.32.158172.16.32.158. Therefore, 172.16.32.130172.16.32.130 and 172.16.32.158172.16.32.158 are both valid, assignable host addresses within the Sales subnet.

Step-by-Step Solution

1
Calculate the Engineering department subnet size and prefix length
Engineering requires 100100 usable host IPs. 27−2=126≥1002^7 - 2 = 126 \ge 100, so 77 host bits are needed, giving a prefix length of /25/25 (32−7=2532 - 7 = 25).
Determining host bit requirements establishes the boundary for sequential allocation.
2
Determine the network block allocated to the Engineering department
The Engineering subnet is 172.16.32.0/25172.16.32.0/25. Network ID: 172.16.32.0172.16.32.0, Usable range: 172.16.32.1172.16.32.1 to 172.16.32.126172.16.32.126, Broadcast address: 172.16.32.127172.16.32.127.
Sequential allocation requires knowing where the Engineering block finishes so the next subnet can start.
3
Calculate the Sales department subnet size and prefix length
Sales requires 2828 usable host IPs. 25−2=30≥282^5 - 2 = 30 \ge 28, so 55 host bits are needed, giving a prefix length of /27/27 (32−5=2732 - 5 = 27).
Establishes the block size for the Sales department subnet.
4
Determine the address boundaries and usable host range for the Sales department subnet
The Sales subnet starts immediately at 172.16.32.128/27172.16.32.128/27. Network ID: 172.16.32.128172.16.32.128, Usable host range: 172.16.32.129172.16.32.129 to 172.16.32.158172.16.32.158, Broadcast address: 172.16.32.159172.16.32.159.
Allows identification of valid usable host IPs versus network/broadcast or out-of-range IPs.
5
Evaluate the candidate options against the calculated usable host range
172.16.32.130172.16.32.130 and 172.16.32.158172.16.32.158 fall strictly within the inclusive range 172.16.32.129172.16.32.129 through 172.16.32.158172.16.32.158.
Matching options to valid host address criteria.

Key Concept

VLSM Subnet Allocation & Host Range Determination
Estimated Time:3m 0s
Rate this question

Topics

IPv4 Addressing and Subnetting

More questions from this topic