200-301 Question #660: Real Exam Question with Answer & Explanation

Question

Drag and Drop Question Refer to Exhibit. The IP address configurations must be completed on the DC-1 and HQ-1 routers based on these requirements: DC-1 Gi1/0 must be the last usable address on a /30 DC-1 Gi1/1 must be the first usable address on a /29 DC-1 Gi1/2 must be the last usable address on a /28 HQ-1 Gil/3 must be the last usable address on a /29 Drag and drop the commands from the left onto the destination interfaces on the right. Not all commands are used. Answer:

Explanation

Subnetting Breakdown

Interface 1 — DC-1 Gi1/0: ip address 209.165.202.130 255.255.255.252

Requirement: Last usable on a /30

• /30 mask = 255.255.255.252 → 4 addresses per subnet, 2 usable
• Subnet: 209.165.202.128/30
  • Network: .128
  • Usable: .129 (first), .130 (last)
  • Broadcast: .131
• Last usable = .130 → correct answer

Common mistake: Choosing .129 (first usable) or .131 (broadcast — not assignable).

Interface 2 — DC-1 Gi1/1: ip address 192.168.4.9 255.255.255.248

Requirement: First usable on a /29

• /29 mask = 255.255.255.248 → 8 addresses per subnet, 6 usable
• Subnet: 192.168.4.8/29
  • Network: .8
  • Usable: .9 (first) through .14 (last)
  • Broadcast: .15
• First usable = .9 → correct answer

Common mistake: Choosing .8 (the network address — not assignable).

Interface 3 — DC-1 Gi1/2: ip address 192.168.3.14 255.255.255.240

Requirement: Last usable on a /28

• /28 mask = 255.255.255.240 → 16 addresses per subnet, 14 usable
• Subnet: 192.168.3.0/28
  • Network: .0
  • Usable: .1 through .14
  • Broadcast: .15
• Last usable = .14 → correct answer, with mask .240

Critical mistake: The address .14 also appears in the /29 option (mask .248). The distinguishing factor here is the subnet mask — this interface requires /28 = .240, not .248.

Interface 4 — HQ-1 Gi1/3: ip address 192.168.3.14 255.255.255.248

Requirement: Last usable on a /29

• /29 mask = 255.255.255.248 → 8 addresses per subnet, 6 usable
• Subnet: 192.168.3.8/29
  • Network: .8
  • Usable: .9 through .14
  • Broadcast: .15
• Last usable = .14 → correct answer, with mask .248

Critical mistake: Same IP (.14) as interface 3, different mask. This is intentional — they're on different subnets (.0/28 vs .8/29). Swapping the masks here is the most common error on this question.

Why the Unused Options Are Wrong

Key Takeaways

1. First usable = network address + 1; Last usable = broadcast - 1
2. When the same IP appears with two different masks, the subnet mask tells you which subnet it belongs to
3. Always derive the broadcast address first to confirm "last usable" — don't guess

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