What is the primary function of a DHCP relay agent in a multi-subnet network?

• A. It assigns IP addresses to clients on each subnet directly.
• B. It blocks DHCP traffic between subnets for security.
• C. It caches DHCP leases locally on the router.
• D. It forwards DHCP discovery messages across subnets to a central DHCP server.

Answer: (D)

In a network with multiple subnets, DHCP uses broadcast messages that don’t cross routers by default, so you need a relay to bridge those broadcasts to a central DHCP server. A DHCP relay agent sits on a router and forwards the client’s DHCP discovery (and subsequent messages) across subnets to the DHCP server, often adding the client’s subnet information so the server can assign an appropriate address. The server responds back through the relay to the client, allowing centralized IP address management across the network. This is why the primary function is to forward DHCP discovery messages across subnets to a central DHCP server. The relay itself doesn’t assign addresses, block DHCP traffic, or cache leases—that’s the job of the DHCP server (and, in a security context, of firewalls or ACLs).