H3C Technologies H3C S5120 Series Switches - Manual (Page 254)

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DHCP Snooping Configuration
When configuring DHCP snooping, go to these sections for information you are interested in:
z DHCP Snooping Overview
z Configuring DHCP Snooping Basic Functions
z Configuring DHCP Snooping to Support Option 82
z Displaying and Maintaining DHCP Snooping
z DHCP Snooping Configuration Examples
The DHCP snooping enabled device does not work if it is between the DHCP relay agent and DHCP
server, and it can work when it is between the DHCP client and relay agent or between the DHCP client
and server.
DHCP Snooping Overview
Functions of DHCP Snooping
As a DHCP security feature, DHCP snooping can implement the following:
1) Ensuring DHCP clients to obtain IP addresses from authorized DHCP servers
2) Recording IP-to-MAC mappings of DHCP clients
Ensuring DHCP clients to obtain IP addresses from authorized DHCP servers
If there is an unauthorized DHCP server on a network, DHCP clients may obtain invalid IP addresses
and network configuration parameters, and cannot normally communicate with other network devices.
With DHCP snooping, the ports of a device can be configured as trusted or untrusted, ensuring the
clients to obtain IP addresses from authorized DHCP servers.
z Trusted: A trusted port forwards DHCP messages normally.
z Untrusted: An untrusted port discards the DHCP-ACK or DHCP-OFFER messages from any
DHCP server.
You should configure ports that connect to authorized DHCP servers or other DHCP snooping devices
as trusted, and other ports as untrusted. With such configurations, DHCP clients obtain IP addresses
from authorized DHCP servers only, while unauthorized DHCP servers cannot assign IP addresses to
DHCP clients.