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C

HAPTER

 57: DHCP C

ONFIGURATION

Figure 165   Sub-option structure

SubOpt: Indicates the number of the sub-option. Sub-options contained in this 
packet are sub-option 1, sub-option 2 and sub-option 5. They have the following 
meanings:

■

Sub-option 1 defines the Circuit ID.

■

Sub-option 2 defines the Remote ID.

■

Sub-option 5 defines the Link Selection.

Len: Indicates the length of the Sub-option Value field.

Sub-option Value: Indicates the sub-option value. For example, the value for 
sub-option 1 is Circuit ID.

DHCP supports option 82. It can add option 82 into the request packets from the 
client to the server to identify the user location information. Only sub-option-1 
and sub-option 2 can be added while sub-option 5 cannot be added currently. In 
the normal mode, sub-option 1 is the layer 2 port number and VLAN ID of the 
received packet, and sub-option 2 is the MAC address of the device to receive 
packets.

In order to locate the users more exactly, we put forward the IP DSLAM user 
physical position location solution for DSLAM application, and define the 3Com 
fixed network mode of the DHCP option 82, where the sub-option 1 of Option 82 
is expressed in the form of "Node identifier + frame number/slot 
number/subslot/port number + vlan", sub-option2 still represents the MAC 
address of the Relay system, and sub-option5 is not added.

The node identifier in the sub-option1 of Option82 is a string, which can adopt 
the MAC address of the administration port of the device by default, in the form 
of 00-E0-FC-0D-DC-EC. You can modify the user node identifiers through