H3C Technologies H3C S10500 Series Switches - Manual (Page 85)

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To do… Use the command… Remarks
Enter Ethernet interface view
interface interface-type
interface-number
—
The interface connects to the DHCP
server.
Specify the port as a trusted port
that records the IP-to-MAC
bindings of clients
dhcp-snooping trust
Required
After DHCP snooping is enabled, a
port is an untrusted port by default
Return to system view quit —
Enter interface view
interface interface-type
interface-number
—
The interface indirectly connects to
the DHCP client.
Specify the port as a trusted port
that does not record the IP-to-MAC
bindings of clients
dhcp-snooping trust
no-user-binding
Optional
After DHCP snooping is enabled, a
port is an untrusted port by default.
Configuring DHCP snooping to support Option 82
Configuration guidelines
Follow these guidelines when configure DHCP snooping to support Option 82:
• You can only enable DHCP snooping to support Option 82 on Layer 2 Ethernet ports, and Layer 2
aggregate interfaces.
• If a Layer 2 Ethernet port is added to an aggregation group, enabling DHCP snooping to support
Option 82 on the interface will not take effect. After the interface quits the aggregation group, the
configuration will be effective.
• Option 82 support requires configuration on both the DHCP server and the device enabled with
DHCP snooping. See the chapter “DHCP server configuration” for DHCP server configuration of
this kind.
• If the handling strategy of the DHCP-snooping-enabled device is configured as replace, you need
to configure a padding format for Option 82. If the handling strategy is keep or drop, you need not
configure any padding format.
• If the Option 82 is padded with the device name, the device name must contain no spaces.
Otherwise, the DHCP-snooping device will drop the message. You can use the sysname command
to specify the device name. For more information about this command, see the Fundamentals
Command Reference.
• If DHCP snooping and QinQ work together or the DHCP snooping device receives a DHCP packet
with two VLAN tags, and the normal or verbose padding format is adopted for Option 82, DHCP
snooping fills the VLAN ID field of sub-option 1 with outer VLAN tag.inter VLAN tag. For example,
if the outer VLAN tag is 10 (a in hexadecimal) and the inner VLAN tag is 20 (14 in hexadecimal),
the VLAN ID is 000a.0014.
Configuration procedure
Follow these steps to configure DHCP snooping to support Option 82:
To do… Use the command… Remarks
Enter system view system-view —