322 | Dynamic Host Configuration Protocol (DHCP)
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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 them via unicast to the DHCP servers; 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 67, and the relay agent rewrites the destination address
and forwards the packet to the client subnet via broadcast or unicast, depending whether the client has set
or cleared the BROADCAST flag in the DHCP Client PDUs.
Figure 13-4. Configuring Dell Force10 Systems as a DHCP Relay Device
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.
Displaying the Helper Address Configuration
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
Note: DHCP Relay is not available on Layer 2 interfaces and VLANs.
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