Which of the following configurations is essential for OSPF routing functionality?

Assigning IP addresses to routers is essential for OSPF (Open Shortest Path First) routing functionality because OSPF is a link-state routing protocol that operates within IP networks. For OSPF to successfully establish neighbor relationships and exchange routing information, each router must have an IP address assigned to its interfaces. This allows the routers to identify and communicate with each other over the network, enabling OSPF to build a topology of the network by sharing link-state information.

The IP addresses on each router's interfaces are used to determine the OSPF area in which a router belongs, helping in the efficient creation of OSPF adjacencies and the dissemination of routing information. Without valid IP addresses, OSPF cannot function because there would be no way for routers to send or receive OSPF hello packets or update messages necessary for maintaining the routing table. Thus, assigning IP addresses is a foundational step required to facilitate OSPF operations.

The other configurations mentioned do not support OSPF's operational requirements, and hence would hinder routing functionality rather than support it.