Dell Force10 S55T S55 Configuration Guide FTOS 8.3.5.3 - Page 242

www.dell.com | support.dell.com Unicast Configure the System to be a Relay Agent Ze The following feature is available on platforms: DHCP clients and servers request and offer configuration information via broadcast DHCP messages. Routers do not forward broadcasts, so if there are no DHCP servers on the subnet, the client does not receive a response to its request and therefore cannot access the network. You can configure an interface on the Dell Force10 system to relay the DHCP messages to a specific DHCP server using the command ip helper-address dhcp-address from INTERFACE mode, as shown in the illustration below. Specify multiple DHCP servers by entering the ip helper-address dhcp-address command multiple times. When ip helper-address is configured, the system listens for DHCP broadcast messages on port 67. The system rewrites packets received from the client and forwards it via unicast; the system rewrites the destination IP address and writes its own address as the relay device. Responses from the server are unicast back to the relay agent on port 68 and the relay agent rewrites the destination address and forwards the packet to the client subnet via broadcast. Note: DHCP Relay is not available on Layer 2 interfaces and VLANs. HCP Relay Device DHCP Server 10.11.2.5 Broadcast Source IP : 10.11.1.5 Destination IP: 255.255.255.255 Source Port: 67 Destination Port: 68 1/3 Broadcast Source IP : 0.0.0.0 Destination IP: 255.255.255.255 Source Port: 68 Destination Port: 67 Relay Agent Address: 0.0.0.0 R1(conf-if-gi-1/3)#show config ! interface GigabitEthernet 1/3 ip address 10.11.0.3/24 ip helper-address 10.11.1.5 ip helper-address 10.11.2.5 no shutdown Unicast DHCP Server Source IP : 10.11.1.5 10.11.1.5 Destination IP: 10.11.0.3 Source Port: 67 Destination Port: 68 1/4 Unicast Source IP : 10.11.1.3 Destination IP: 10.11.1.5 Source Port: 67 Destination Port: 67 Relay Agent Address: 10.11.0.3 DHCP 001 242 | Dynamic Host Configuration Protocol (DHCP)