S1 has just been discovered by APIC1. No other spine switches have yet been discovered. Which of the following best describes the switches that might have been discovered before S1?

• 350-601 : All Parts

Most likely, L1 was discovered before S1 in this scenario because of the way that Cisco Application Policy Infrastructure Controllers (APICs) discover and register leaf and spine switches in a Cisco Application Centric Infrastructure (ACI) fabric. When a Cisco APIC begins the switch discovery process, it first detects only the leaf switch to which it is connected. After that leaf switch is registered, the APIC discovers each of the spine switches to which the leaf switch is connected. Spine switches do not automatically register with the APIC. When a spine switch is registered with the APIC, the APIC will discover all the leaf switches that are connected to that spine switch. Therefore, APIC1 will not discover all the leaf switches in this scenario until each spine switch is registered with the APIC.

S2 will be discovered by APIC1 next in this scenario; it was not discovered before S1. In this scenario, APIC1 has just discovered S1. This means that L1, the leaf switch to which APIC1 is directly connected, has already been discovered as well. L1 is directly connected to both spine switches in the topology. Because S1 was just discovered and no other spine switches have yet been discovered, it is likely that APIC1 will next discover S2.
APIC1 will not discover L2, L3, L4, L5, or L6 before it discovers S1 in this scenario. All these switches are leaf switches that are directly connected to both S1 and S2. However, none of these leaf switches are directly connected to APIC1. Although APIC1 in this scenario will eventually discover L2, L3, L4, L5, and L6, it will first discover all the spine switches to which L1 is directly connected because APIC1 is directly connected to L1.