User Manual UMN:CLIV81024079.6.4 DHCP Relay AgentA DHCP relay agent is any host that forwards DHCP packets between clients and servers.The DHCP relay agents are used to forward DHCP requests and replies between clientsand servers when they are not on the same physical subnet. The DHCP relay agent for-warding is distinct from the normal forwarding of an IP router, where IP datagrams areswitched between networks somewhat transparently.By contrast, DHCP relay agents receive DHCP messages and then generate a newDHCP message to send out on another interface. The DHCP relay agent sets the gate-way address and, if configured, adds the DHCP option 82 information in the packet andforwards it to the DHCP server. The reply from the server is forwarded back to the clientafter removing the DHCP option 82 information.Fig. 9.37 Example of DHCP Relay AgentTo activate/deactivate the DHCP function in the system, use the following command.Command Mode Descriptionservice dhcp Global Activates the DHCP function in the system.no service dhcp Deactivates the DHCP function in the system.Before configuring DHCP server or relay, you need to use the service dhcp commandfirst to activate the DHCP function in the system.9.6.4.1 DHCP Helper AddressA DHCP client sends DHCP_DISCOVER message to a DHCP server. DHCP_DISCOVERmessage is broadcasted within the network to which it is attached. If the client is on anetwork that does not have any DHCP server, the broadcast is not forwarded becausei
