DHCP Relay gives the switch the ability to forward DHCP messages from one VLAN or VRF to a DHCP server that resides in a different network thereby increasing the size of the network that the DHCP server (hosted or external) services.
DHCP Relay overcomes a limitation that exists due to the fact that, under the default configuration, the switch does not forward UDP broadcasts to different VLANs or VRFs. If a client broadcasts a DHCP Discover message to request an IP address from any connected DHCP server, the broadcast would fail unless there is a DHCP server in the same VLAN. When DHCP Relay is configured, the switch can receive the broadcast in one VLAN or VRF and retransmit the message as a unicast message to the IP address of a remote DHCP server. The switch also relays the server response back to the client.
The following conditions exist for this feature:
You can configure DHCP Relay whether you're deploying the hosted DHCP Server feature or if you're deploying an external DHCP server.
Supports the relay of either DHCP or Bootstrap (BOOTP) messages (default behavior is to relay both message types).
Supports Smart Relay, which turns DHCP Relay on for secondary addresses also.
You can configure the relay using global DHCP settings or using port or VLAN settings.
When you deploy DHCP Relay with the hosted DHCP Server feature, you can configure the relay on the same switch that hosts DHCP Server (local relay) or on a neighboring switch (remote relay). In either case, configure the the relay forwarding path to point to the management CLIP IP interface where DHCP Server listens.
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