Dell Force10 S4820T S4820T Configuration Guide - Page 350

www.dell.com | support.dell.com Unicast 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 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 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 DHCP 001 To view the ip helper-address configuration for an interface, use the command show ip interface from EXEC privilege mode, as shown in the following example. R1_E600#show ip int gig 1/3 GigabitEthernet 1/3 is up, line protocol is down Internet address is 10.11.0.1/24 Broadcast address is 10.11.0.255 Address determined by user input IP MTU is 1500 bytes Helper address is 192.168.0.1 192.168.0.2 Directed broadcast forwarding is disabled Proxy ARP is enabled Split Horizon is enabled Poison Reverse is disabled ICMP redirects are not sent ICMP unreachables are not sent 350 | Dynamic Host Configuration Protocol (DHCP)