Refer to the topology and the provided configurations. Router R6 does not form an EIGRP neighbor relationship correctly with router R1. What is the cause for this misconfiguration?

K value mismatches would cause EIGRP neighbor formation to fail with a 'K-value mismatch' log message, but the question context points to a missing configuration rather than a metric parameter conflict.

AS number mismatches prevent EIGRP peering, but routers in different AS numbers would still attempt and visibly reject Hello packets - the symptom here is that no relationship forms at all due to a missing command.

EIGRP will not activate on an interface or advertise that interface's network unless a matching 'network' command is configured under the EIGRP process. Without this command on R6, the interface facing R1 is excluded from EIGRP entirely, preventing neighbor discovery and adjacency formation.

The passive-interface command stops EIGRP from sending Hellos on an interface but is an explicit configuration action, not a missing one; the scenario describes a misconfiguration by omission.