Dhcp-Snooping Option 82; Overview Of Dhcp-Snooping Option 82 - H3C S7500 Series Operation Manual

Operation Manual – DHCP
H3C S7500 Series Ethernet Switches
Enter system view
Enable the DHCP
snooping function
Enter Ethernet port view
Set the port connected to
a DHCP server to a
trusted port
Note:
DHCP relay agent and DHCP snooping cannot be enabled at the same time. If you
have enabled DHCP relay agent on the device, you will fail to enable DHCP
snooping.
The dhcp-snooping trust command and the dhcp-snooping command must be
configured at the same time; otherwise DHCP packets may be dropped in actual
networking.

4.2 DHCP-Snooping Option 82

4.2.1 Overview of DHCP-Snooping Option 82

I. Introduction to DHCP Option 82
For details of option 82, see
II. Working mechanism of DHCP-Snooping option 82
The process in which a DHCP client obtains an IP addresses from a DHCP server
through DHCP-Snooping is the same as the process in which a DHCP client obtains an
IP address from a DHCP server directly. The process includes four phases: IP lease
request, IP lease offer, IP lease selection, and IP lease acknowledgement. This section
only introduces the working mechanism of DHCP-Snooping option 82. The details are
as follows:
1) When a DHCP client gets online, it broadcasts an IP address request message
across the network.
2) After receiving the broadcast message, the DHCP-Snooping-enabled switch
checks whether the message contains option 82 and processes it.
To do...
system-view
dhcp-snooping
interface interface-type
interface-number
dhcp-snooping trust
Option 82
Chapter 4 DHCP Snooping Configuration
Use the command...
Supporting.
4-3
Remarks
—
Required
By default, the DHCP
snooping function is
disabled
—
Required
By default, all ports of a
switch are untrusted ports