HPE7-A04 · Question #16
In a Spine and Leaf Design with the following specs: - 8400 100G Spine Switches - 8360 48-P 10G RJ45 Leaf Switches - 100G DAC connections between Spine and Leafs Spine Switches = 8400 with 12 QSFP28…
The correct answer is A. Solution can scale to 24 total racks using the same subscription rates. Option A is correct because each spine switch has 48 available 100G QSFP28 ports, and in this design leaf switches are deployed in VSX pairs - two leaf switches per rack connected via 2x ISL DACs. Dividing the 48 available spine ports by 2 leaf switches per rack gives a maximum…
Question
In a Spine and Leaf Design with the following specs:
- 8400 100G Spine Switches
- 8360 48-P 10G RJ45 Leaf Switches
- 100G DAC connections between Spine and Leafs
Spine Switches = 8400 with 12 QSFP28 ports (F-B airflow) Each Spine Switch uses:
- 1 x 100G QSFP28 5M DACs to each Leaf switch
Each Leaf Switch uses:
- 1 x 100G QSFP28 5M DACs to each Spine switch
- 2 x 100G 1M DAC for ISL
- 1 x 10G RJ45 for Keep alive
Each Spine switch can support up to 48 available 100G QSFP28 interfaces. What is the scalability for this solution?
Options
- ASolution can scale to 24 total racks using the same subscription rates.
- BSolution can scale to 6 total racks using the same subscription rates.
- CSolution can scale to 12 total racks using the same subscription rates.
- DSolution can scale to 48 total racks using the same subscription rates.
How the community answered
(20 responses)- A65% (13)
- B5% (1)
- C10% (2)
- D20% (4)
Explanation
Option A is correct because each spine switch has 48 available 100G QSFP28 ports, and in this design leaf switches are deployed in VSX pairs - two leaf switches per rack connected via 2x ISL DACs. Dividing the 48 available spine ports by 2 leaf switches per rack gives a maximum of 24 racks while maintaining the same subscription ratio across the fabric.
Why the distractors are wrong:
- D (48 racks) is the most common trap - it assumes one leaf switch per rack, ignoring the VSX pair requirement signaled by the 2x ISL ports on each leaf.
- C (12 racks) likely comes from halving the correct answer, perhaps by mistakenly counting 4 ports consumed per rack instead of 2.
- B (6 racks) may result from dividing 48 spine ports by 8 (the number of spine switches), which conflates spine switch count with port availability.
Memory tip: Whenever you see "2x ISL DAC" on a leaf switch, that's your cue that leaves are paired - so always divide total spine downlink ports by 2 to get rack count: 48 ports ÷ 2 leaves/rack = 24 racks.
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