H3C Technologies H3C S10500 Series Switches - Manual (Page 67)

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Figure 30 DHCP relay agent work process
1. After receiving a DHCP-DISCOVER or DHCP-REQUEST broadcast message from a DHCP client,
the DHCP relay agent fills the giaddr field of the message with its IP address and forwards the
message to the designated DHCP server in unicast mode.
2. Based on the giaddr field, the DHCP server returns an IP address and other configuration
parameters to the relay agent, and the relay agent conveys them to the client.
DHCP relay agent support for Option 82
Option 82 records location information of the DHCP client, letting the administrator locate the DHCP
client for security control and accounting purposes. For more information, see the chapter “DHCP
overview.”
If the DHCP relay agent supports Option 82, it handles a client’s request according to the contents
defined in Option 82, if any. The handling strategies are described in Table 3 .
If a reply returned by the DHCP server contains Option 82, the DHCP relay agent removes the Option 82
before forwarding the reply to the client.
Table 3 Handling strategies of the DHCP relay agent
If a client’s
requesting
message has…
Handling
strategy
Padding format The DHCP relay agent will…
Drop Random Drop the message.
Keep Random
Forward the message without changing
Option 82.
normal
Forward the message after replacing the
original Option 82 with the Option 82
padded in normal format.
verbose
Forward the message after replacing the
original Option 82 with the Option 82
padded in verbose format.
Option 82
Replace
user-defined
Forward the message after replacing the
original Option 82 with the user-defined
Option 82.