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7.8.1.0 - Force10 Networks

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Chapter 9<br />

Dynamic Host Configuration Protocol is supported on platforms: c e s<br />

Secure DHCP is supported only on platforms: c s<br />

Relay DHCP Messages<br />

Dynamic Host Configuration<br />

Protocol<br />

DHCP clients and servers request and offer configuration information via broadcast DHCP messages.<br />

Routers do not forward broadcasts, so if there are no DHCP servers on the subnet, the client does not<br />

receive a response to its request and therefore cannot access the network.<br />

You can configure an interface on the <strong>Force10</strong> system to relay the DHCP messages to a specific DHCP<br />

server using the command ip helper-address dhcp-address from INTERFACE mode, as shown in<br />

Figure 165. Specify multiple DHCP servers by entering the ip helper-address dhcp-address command<br />

multiple times.<br />

When ip helper-address is configured, the system listens for DHCP broadcast messages on port 67. The<br />

system rewrites packets received from the client and forwards it via unicast; the system rewrites the<br />

destination IP address and writes its own address as the relay device. Responses from the server are unicast<br />

back to the relay agent on port 68, and the relay agent rewrites the destination address and forwards the<br />

packet to the client subnet via broadcast.<br />

Note: DHCP Relay is not available on Layer 2 interfaces and VLANs.<br />

FTOS Configuration Guide, version <strong>7.8.1.0</strong> 279

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