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When receiving a DHCP client’s request without Option 82, the DHCP snooping device will add the
option field with the configured sub-option and then forward the packet. For details, see
Table 3-2.
Table 3-2 Ways of handling a DHCP packet without Option 82
Sub-option configuration The DHCP-Snooping device will …
Neither of the two sub-options is
configured.
Forward the packet after adding Option 82 with the default
contents.
The format of Option 82 is the one specified with the
dhcp-snooping information format command or the default
HEX format if this command is not executed.
Circuit ID sub-option is configured.
Forward the packet after adding Option 82 with the configured
circuit ID sub-option in ASCII format.
Remote ID sub-option is configured.
Forward the packet after adding Option 82 with the configured
remote ID sub-option in ASCII format.
The circuit ID and remote ID sub-options in Option 82, which can be configured simultaneously or
separately, are independent of each other in terms of configuration sequence.
When the DHCP snooping device receives a DHCP response packet from the DHCP server, the DHCP
snooping device will delete the Option 82 field, if contained, before forwarding the packet, or will directly
forward the packet if the packet does not contain the Option 82 field.
Configuring DHCP Snooping
Configuring DHCP Snooping
Follow these steps to configure DHCP snooping:
To do… Use the command… Remarks
Enter system view
system-view
—
Enable DHCP snooping
dhcp-snooping
Required
By default, the DHCP snooping
function is disabled.
Enter Ethernet port view
interface interface-type
interface-number
—
Specify the current port as a
trusted port
dhcp-snooping trust
Required
By default, after DHCP
snooping is enabled, all ports of
a switch are untrusted ports.