PLANET XGS3-24040 - Manual (Page 232)

Chapter 31 DHCP Snooping Configuration
30-4
3. Enable the DHCP option 82 of server.
Command Explanation
Global mode
ip dhcp server relay information enable
no ip dhcp server relay information
enable
This command is used to enable the switch
DHCP server to identify option82. The “no
ip dhcp server relay information enable”
command will make the server ignore the
option 82.
4. Diagnose and maintain DHCP option 82
Command Explanation
Admin mode
show ip dhcp relay information option
This command will display the state
information of the DHCP option 82 in the
system, including option82 enabling switch,
the interface retransmitting policy, the
circuit ID mode and the DHCP server
option82 enabling switch.
debug ip dhcp relay packet
This command is used to display the
information of data packets processing in
DHCP Relay Agent, including the “add” and
“peel” action of option 82.
30.3 DHCP option 82 Application Examples
Figure 3-1 A DHCP option 82 typical application example
In the above example, layer 2 switches Switch1 and Switch2 are both connected to layer 3 switch Switch3,
Switch 3 will transmit the request message from DHCP client to DHCP serer as DHCP Relay Agent. It will also
transmit the reply message from the server to DHCP client to finish the DHCP protocol procedure. If the
DHCP option 82 is disabled, DHCP server cannot distinguish that whether the DHCP client is from the
network connected to Switch1 or Switch2. So, all the PC terminals connected to Switch1 and Switch2 will get
addresses from the public address pool of the DHCP server. After the DHCP option 82 function is enabled,
Switch1
Switch2
DHCP Client PC1
DHCP Client PC2
DHCP Server
Vlan2:ethernet1/2
Vlan2:ethernet1/3
DHCP Relay Agent
Switch3
Vlan3