In your design, you have six racks each with a pair of VSX Leaf switches and two Spine switches. How many P2P leaf-to-spine addresses are there?

Question

Options

• A12
• B96
• C24
• D48

• A
  15% (5)
• B
  9% (3)
• C
  27% (9)
• D
  48% (16)

Explanation

Option D (48) is correct because the design has 6 racks × 2 VSX leaf switches = 12 physical leaf switches, each connecting to both spine switches, yielding 12 × 2 = 24 P2P links. Each P2P link uses a /31 subnet providing 2 IP addresses (one per endpoint), so 24 links × 2 addresses = 48 total P2P addresses.

Why the distractors fail:

• A (12) only counts the total number of leaf switches - it ignores the spine connections and per-link addressing entirely.
• C (24) correctly counts the number of P2P links but stops there, forgetting that each link consumes two addresses.
• B (96) likely comes from mistakenly using /30 subnets (4 addresses each instead of 2), giving 24 × 4 = 96 - but P2P links use /31s in modern designs.

Memory tip: Work in three steps - racks × 2 leaves = total leaves → leaves × spines = links → links × 2 = addresses. The "×2" appears twice (VSX pairs, then /31 endpoints), so the final answer is always 4× the rack count: 6 × 8 = 48.

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