When clients on a different VLAN cannot receive DHCP addresses, it's often because there is no DHCP helper address configured on the router or switch. A DHCP relay/helper address forwards DHCP requests from clients on the VLAN to the DHCP server, which may reside on a different network. * Confirming the network has a helper address (Answer C): This should be the first step to ensure that DHCP requests from the VLAN are correctly routed to the DHCP server. * Checking client NIC speed (Option A): While important, incorrect NIC speed wouldn't affect the ability to obtain an IP address from DHCP. * Checking NTP server (Option B): Time synchronization is unrelated to DHCP issues. * Authorizing the DHCP server (Option D): This is essential for DHCP operation, but since this is an existing DHCP cluster, the helper address is more likely the issue. CompTIA Server+ Reference:This topic is related to SK0-005 Objective 1.2: Manage server network connections.