CLI Reference Guide-R05

Chapter 9 | General Security Measures
DHCP Snooping
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Command Usage
The format for TR101 option 82 is: “<IP> eth <SID>/<PORT>[:<VLAN>]”. Note that
the SID (Switch ID) is always 0. By default the PVID is added to the end of the TR101
field for untagged packets. For tagged packets, the VLAN ID is always added. Use
the ip dhcp snooping information option remote-id tr101 no-vlan-field
command to remove the VLAN ID from the end of the TR101 field for untagged
packets. Use the no form of this command to add the PVID for untagged packets at
the end of the TR101 field.
Example
This example sets the remote ID to the switch’s IP address.
Console(config)#ip dhcp snooping information option remote-id tr101
node-identifier ip
Console(config)#
ip dhcp snooping
information policy
This command sets the DHCP snooping information option policy for DHCP client
packets that include Option 82 information. Use the no form to restore the default
setting.
Syntax
ip dhcp snooping information policy {drop | keep | replace}
no ip dhcp snooping information policy
drop - Drops the client’s request packet instead of relaying it.
keep - Retains the Option 82 information in the client request, and
forwards the packets to trusted ports.
replace - Replaces the Option 82 information circuit-id and remote-id fields
in the client’s request with information about the relay agent itself, inserts
the relay agent’s address (when DHCP snooping is enabled), and forwards
the packets to trusted ports.
Default Setting
replace
Command Mode
Global Configuration
Command Usage
When the switch receives DHCP packets from clients that already include DHCP
Option 82 information, the switch can be configured to set the action policy for
these packets. The switch can either drop the DHCP packets, keep the existing
information, or replace it with the switch’s relay information.