H3C Technologies H3C S12500 Series Switches - Manual (Page 92)

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Step Command Remarks
3. Enter Ethernet interface view.
interface interface-type
interface-number The interface connects to the DHCP
server.
4. Specify the port as a trusted port
that records the IP-to-MAC
bindings of clients. dhcp-snooping trust
After DHCP snooping is enabled, a
port is an untrusted port by default.
5. Return to system view. quit N/A
6. Enter interface view.
interface interface-type
interface-number The interface indirectly connects to
the DHCP client.
7. 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 you configure DHCP snooping to support Option 82:
• You can configure DHCP snooping to support Option 82 on Layer 2 Ethernet interfaces or Layer 2
aggregate interfaces only.
• If a Layer 2 Ethernet interface 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.
• To support Option 82, perform related configuration on both the DHCP server and the switch
enabled with DHCP snooping. For DHCP server configuration of this kind, see "
Configuring the
DHCP server ."
• If the handling strategy of the DHCP-snooping-enabled switch 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 contains the device name (sysname) of a node, the device name must contain no
spaces. Otherwise, the DHCP-snooping-enabled switch will drop the message. You can use the
sysname command to specify the device name. For more information about this command, see
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
To configure DHCP snooping to support Option 82: