H3C Technologies H3C S12500 Series Switches - Manual (Page 74)

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Table 4 Handling strategies
If a DHCP request
has…
Handling
strategy
DHCP snooping…
Option 82
Drop Drops the message.
Keep Forwards the message without changing Option 82.
Replace
Forwards the message after replacing the original Option 82 with
the Option 82 padded according to the configured padding format,
padding content, and code type.
No Option 82 N/A
Forwards the message after adding the Option 82 padded
according to the configured padding format, padding content, and
code type.
72B
DHCP snooping configuration task list
If you configure DHCP snooping settings on a Layer 2 Ethernet interface that has been added to an
aggregation group, the settings do not take effect unless the interface is removed from the aggregation
group.
Tasks at a glance
(Required.)
715H
Configuring basic DHCP snooping
(Optional.)
Configuring Option 82
(Optional.)
717H
Saving DHCP snooping entries
(Optional.)
Enabling DHCP starvation attack protection
(Optional.)
719H
Enabling DHCP-REQUEST attack protection
73B
Configuring basic DHCP snooping
Follow these guidelines when you configure basic DHCP snooping:
• Specify the ports connected to authorized DHCP servers as trusted ports to make sure that DHCP
clients can obtain valid IP addresses. The trusted ports and the ports connected to DHCP clients
must be in the same VLAN.
• Layer 2 Ethernet interfaces and Layer 2 aggregate interfaces can be specified as trusted ports. For
more information about aggregate interfaces, see Layer 2—LAN Switching Configuration Guide.
• If you configure DHCP snooping settings on a Layer 2 Ethernet interface that has been added to an
aggregation group, the settings do not take effect unless the interface is removed from the
aggregation group.
• DHCP snooping can work with basic QinQ or flexible QinQ to record VLAN tags for DHCP
packets received from clients. Upon receiving a DHCP packet that has one VLAN tag, QinQ adds
an outer tag to the packet. DHCP snooping records the two VLAN tags of the packet in a DHCP
snooping entry. However, if you configure flexible QinQ to also modify the original VLAN ID of the
packet, DHCP snooping cannot record the VLAN tags. For more information about QinQ, see
Layer 2—LAN Switching Configuration Guide.