3Com 8807 Configuration Manual page 700

700 C 57: DHCP C
HAPTER
n
c
Displaying and
Debugging DHCP Relay
ONFIGURATION
The DHCP client applies for an IP address through the DHCP relay. When the
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packet from DHCP client passes the DHCP relay, the DHCP relay adds its
primary IP address in the packet and forwards the packet to the DHCP server.
When receiving the packet, DHCP server allocates an IP address in the same
segment as the IP address added by the DHCP relay.
If there is a local DHCP Server, when the DHCP Client applies for IP addresses, it
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can be assigned with only the address which is in the same network segment
with the primary IP address of the interface connecting the client to the server.
The client cannot be assigned with the address which is in the same network
segment with the secondary IP address of the interface connecting the client to
the server.
If there is no local DHCP Server, when the DHCP client applies for IP address
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through Relay, the DHCP Serer can be assigned with only the address which is
in the same network segment with the primary IP address of the Relay. The
DHCP Server cannot be assigned with the address which is in the same
network segment with the secondary IP address of the Relay.
Enable/Disable DHCP security on a VLAN interface
If you enable the DHCP security feature on a VLAN interface, the switch performs
user address checking on the VLAN interface to prevent unauthorized binding
request. If you disable the DHCP security feature on a VLAN interface, the switch
does not perform user address checking on the VLAN interface.
Perform the following configuration in VLAN interface view.
Table 652 Enable/disable DHCP security on a VLAN interface
Operation
Enable DHCP security on a VLAN interface
Disable DHCP security on a VLAN interface
The DHCP security feature is disabled on a VLAN interface by default.
CAUTION: After the DHCP security feature is enabled on a VLAN interface, the
client that has already obtained an IP address will lose its access right and has to
apply for an IP address again. Therefore, it is recommended that the administrator
should conduct this configuration before any user has obtained an IP address.
After the above configuration, you can execute the display command in any view
to display running information about DHCP Relay to verify your configuration.
Execute the debugging command in user view to debug DHCP Relay.
Table 653 Display and debug DHCP Relay
Operation
Display information about the DHCP relay
configured for VLAN interface
Display information about legal user address
entries for DHCP relay
Command
dhcp relay security address-check enable
dhcp relay security address-check disable
Command
display dhcp relay address { interface
vlan-interface vlan-id | all }
display dhcprelay-security [ ip-address ]