H3C Technologies H3C S12500 Series Switches - Manual (Page 71)

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Figure 31 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 the location information about the DHCP client, letting the administrator locate the
DHCP client for security control and accounting purposes. For more information, see "
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…
Option 82
Drop Random Drops the message.
Keep Random
Forwards the message without changing
Option 82.
Replace
normal
Forwards the message after replacing the
original Option 82 with the Option 82 padded
in normal format.
verbose
Forwards the message after replacing the
original Option 82 with the Option 82 padded
in verbose format.
user-defined
Forwards the message after replacing the
original Option 82 with the user-defined
Option 82.
no Option 82 N/A normal
Forwards the message after adding the Option
82 padded in normal format.