Which two scenarios might prevent an IS-IS adjacency from forming?

In the context of IS-IS (Intermediate System to Intermediate System) routing protocol, one important factor that can affect the formation of an IS-IS adjacency is the Maximum Transmission Unit (MTU) settings on the interfaces. When the MTU on an interface is set lower than the expected value of 1492 bytes, it can prevent adjacency from forming if the connecting routers are unable to handle the different MTU settings. IS-IS uses the MTU to ensure that it can transmit data packets without fragmentation; if one device has a different MTU size than its neighbor, it can lead to packet drops or other connectivity issues that prevent the adjacency from being established.

In contrast, the other scenarios listed revolve around configurations that relate to IP addressing and area mismatches in the IS-IS hierarchy. Although having an IP address configured is generally necessary for routing, the main focus for adjacency formation in IS-IS is on the IS-IS-specific configurations, such as mismatches in Level 1 and Level 2 areas. These mismatches can indeed prevent adjacency from forming; however, the correct choice emphasizes an MTU-related issue, which is a fundamental aspect of the link layer interactions before any IS-IS states can be established.

This understanding is