Refer to the exhibit. Which option is discovered after L1 registers to APIC 1?

While Spine 1 (S1) is a fabric component that will eventually be discovered, the question asks what is discovered *after* L1 registers; if L2 is a direct neighbor of L1 in the exhibit, its discovery is a direct consequence of L1 reporting its adjacencies.

The OOB MGMT switch is external to the ACI fabric's data plane and is not discovered as part of the fabric component discovery process.

APIC 2 is another controller node for the APIC cluster, and its discovery is part of cluster formation, which is separate from fabric switch discovery initiated by a leaf registering.

After Leaf 1 (L1) registers with APIC 1, L1 shares its Link Layer Discovery Protocol (LLDP) neighbor information with the APIC. If Leaf 2 (L2) is directly connected to L1, L2 will be discovered by the APIC through L1's reported adjacencies, expanding the fabric topology.