Under which hierarchy do you configure OSPF?

To configure OSPF (Open Shortest Path First) in Junos OS, the correct hierarchy is indeed under the "edit protocols igp" subtree. OSPF is classified as an Interior Gateway Protocol (IGP), which is why it falls under this specific configuration hierarchy.

When you are in the "edit protocols igp" context, you can set various OSPF parameters such as OSPF areas, network types, and interfaces that you want OSPF to operate on. This hierarchy is designed to organize IGP settings, allowing for a streamlined approach when dealing with protocols that function within the same routing domain.

The other choices pertain to different aspects of router configuration. For instance, "edit protocols ospf" would imply a direct hierarchy for OSPF configuration, but OSPF is actually grouped under IGP due to its function and the context needed for configuration. "Edit routing-options" is used for general routing options that apply to multiple protocols, and "edit routing-protocols" may deal with protocols in a broader sense without specifically targeting IGPs. Thus, choosing "edit protocols igp" ensures that you are configuring OSPF settings in the appropriate context for optimal routing functionalities.