What is DHCP relay (IP helper) and why is it used?

• A. It blocks DHCP broadcast messages to preserve bandwidth.
• B. It forwards DHCP broadcast messages from clients to a centralized DHCP server in a different subnet.
• C. It assigns IP addresses to clients directly.
• D. It replaces the DHCP server with a local router.

Answer: (B)

DHCP relay (IP helper) is used when clients on one subnet need IP addresses from a DHCP server that sits on another subnet. A router interface that has DHCP relay enabled listens for DHCP broadcasts from clients and forwards those messages to the central DHCP server, usually using the server’s address and the standard DHCP ports. The relay adds its own address into the packet so the server knows which subnet the client is on, then the server replies back through the relay, which forwards the response on the local network to the client. This lets you manage IP addresses from a single DHCP server across many subnets without placing a server on every segment.

So, the relay’s job isn’t to block broadcasts, assign addresses itself, or replace the DHCP server. It simply bridges the gap, enabling centralized DHCP provisioning across multiple subnets.