The clients and OHCP server reside on different subnets. Which command must be used to forward requests and replies between clients on the 10.10.0.1/24 subnet and the DHCP server at 192.168.10.1?

The `ip route` command is used to establish static routing entries and does not specifically address the forwarding of broadcast DHCP requests across subnets.

The `ip default-gateway` command is typically used on an end device or a Layer 2 switch for its own management traffic, not on a router to forward client DHCP requests.

DHCP requests are broadcast messages that do not traverse router boundaries by default. The `ip helper-address` command, configured on the router interface connected to the client subnet, intercepts these broadcasts and converts them into unicast packets, forwarding them to the specified DHCP server at 192.168.10.1.

The `ip dhcp address` command is not a standard Cisco IOS command for configuring DHCP relay functionality; it might be part of configuring a DHCP server on the router itself, which is not the goal here.