3com S7906E Manuel De Montage

 

3-2 

Figure 3-2 DHCP relay agent work process 

 

 

As shown in 

, the DHCP relay agent works as follows: 

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, which conveys them to the client. 

Option 82 records the location information of the DHCP client. The administrator can locate the DHCP 

client to further implement security control and accounting. For more information, refer to 

. 

If the DHCP relay agent supports Option 82, it will handle a client’s request according to the contents 

defined in Option 82, if any. The handling strategies are described in the table below. 

If a reply returned by the DHCP server contains Option 82, the DHCP relay agent will remove the Option 

82 before forwarding the reply to the client. 

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.