Relay agents and routers

You can use Dynamic Host Configuration Protocol (DHCP) relay agents and routers to efficiently and securely transfer data throughout the network.

Initially, DHCP clients broadcast their DHCPDISCOVER packets because they do not know what network they are connected to. In some networks, the DHCP server might not be on the same LAN as the client. Therefore, it is necessary to forward the client's broadcast DHCP packets to the LAN where the DHCP server is located. Some routers are configured to forward DHCP packages. If your router supports DHCP packet forwarding, your router forwards the DHCP packets to the LAN where the DHCP server is located. However, many routers do not support forwarding packets that have a destination IP address of the broadcast address (DHCP packets). In this case, the LAN must have a Bootstrap protocol (BOOTP)/DHCP relay agent to forward the DHCP packets to the LAN that has the DHCP server. See Scenario: DHCP and PPP profile on different IBM i models for a sample network using a relay agent and a router.

In either case, because the DHCP server is on a separate network, your clients must have the IP address of the router that connects your clients’ network to the network that has the DHCP server specified in the router option (option 3).

In these scenarios, if you do not use a BOOTP/DHCP relay agent, you will need to add a DHCP server to the other LAN to serve those clients. To help you decide how many DHCP servers to have in your network, refer to Network topology considerations.