R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

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Figure 28 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 in a response to the relay agent, and the relay agent conveys it to the client.
DHCP relay agent support for Option 82
Option 82 records the location information about the DHCP client. It enables the administrator to locate
the DHCP client for security control and accounting purposes. For more information, see "Relay agent
opti
on (Option 82)."
If the DHCP relay agent supports Option 82, it handles a DHCP request according to Option 82, if any.
The handling strategies are described in Table 3.
If a r
esponse returned by the DHCP server contains Option 82, the DHCP relay agent removes the Option
82 before forwarding the response to the client.
Table 3 Handling strategies of the DHCP relay agent
If a DHCP request
has…
Handling
strate
gy
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 Option 82
padded in normal format.