Enabling Dhcp-Snooping Option 82 - H3C S7500 Series Operation Manual

Operation Manual – DHCP
H3C S7500 Series Ethernet Switches
If the message contains option 82, the switch replaces the original option 82 in the
message with its own option 82, and then broadcasts the request message.
If the request message does not contain option 82, the DHCP-Snooping-enabled
switch inserts option 82 into the message, and then broadcast this message.
3) By now, the request message contains the number of the switch port connected to
the DHCP client, the VLAN to which the port belongs to, and the MAC address of
the DHCP-Snooping-enabled switch.
4) After
DHCP-Snooping-enabled device, the DHCP server records the information
carried by the options in the message, and then sends the message containing
DHCP
DHCP-Snooping-enabled device.
5) After
DHCP-Snooping-enabled switch checks the option 82 field in the message.
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.
Note:
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.

4.2.2 Enabling DHCP-Snooping Option 82

I. 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.
receiving the DHCP
configuration information
receiving the returned
Chapter 4 DHCP Snooping Configuration
request message
and option
message from
4-4
broadcast by
82 information to
the DHCP server,
the
the
the