An engineer configures an L3Out between BLeaf1 and Core1. A Cisco Nexus 9000 Series Switch runs in NX-OS mode, and the two devices must peer using OSPF. The devices in the network are configured as…

Setting an Auth Key on Core1 would only be necessary if OSPF authentication was enabled and mismatched, which is not indicated as the problem here.

OSPF adjacency requires several parameters to match between peering routers, and the OSPF Area ID is one of the most fundamental. Core1 is explicitly configured for OSPF Area 1, but BLeaf1's OSPF is enabled with default settings, which typically implies Area 0 (the backbone area). Therefore, configuring Area 1 on BLeaf1 is essential to resolve the area mismatch and allow OSPF adjacency to form.

Disabling the Hello Timer on BLeaf1 would prevent OSPF from sending hello packets, which are necessary for neighbor discovery and maintaining adjacency, thus breaking it.

While mismatched MTU can prevent OSPF adjacency, there is no information to suggest an MTU issue, and the explicit area ID mismatch is a more direct cause based on the provided configuration details.