3Com Switch 7750 Configuration Guide Guide

590 CHAPTER 56: DHCP SNOOPING CONFIGURATION
■ If the option 82 field is inserted by the switch, the switch removes the option
82 field from the message, and then forwards the message containing the
DHCP configuration information to the DHCP client.
■ If the option 82 field is not inserted by the switch, the switch obtains the VLAN
information contained in this field and broadcasts the returned message in this
VLAN.
n
There are two types of request messages from a DHCP client: DHCP_DISCOVER
and DHCP_REQUEST. The DHCP servers of different vendors process the request
messages differently. Some devices process the option 82 information in the
DHCP_DISCOVER message, whereas other devices process the option 82
information in the DHCP_REQUEST message, so a DHCP-Snooping-enabled switch
inserts option 82 into both messages.
Enabling
DHCP-Snooping Option
82
Configuration prerequisites
Before configuring DHCP-Snooping option 82, you need to:
Configure network parameters of the DHCP-Snooping-enabled switch.
Enable DHCP-Snooping.
Configure network parameters of the DHCP server, address pool, and address
lease time, and other address assignment policies.
Enabling DHCP-Snooping option 82
Perform the following configuration on a DHCP-Snooping-enabled network
device.
Displaying and
Debugging
DHCP-Snooping
After the above-mentioned configuration, you can use the display command in
any view to display the running status after the DHCP relay is configured. Use the
reset command in user view to clear the IP/MAC mapping relations recorded by
the DHCP-Snooping-enabled switch.
Tabl e 461 Enable DHCP-Snooping option 82
Operation Command Description
Enter system view system-view -
Enable DHCP-Snooping
option 82
dhcp-snooping information
enable
Required
This function is disabled by
default