CLI Reference Guide-R03

Chapter 8 | General Security Measures
DHCP Snooping
– 277 –
■
vlan - Tag of the VLAN which received the DHCP request.
Note that the sub-type and sub-length fields can be enabled or disabled
using the ip dhcp snooping information option command.
■
The ip dhcp snooping information option circuit-id command can be
used to modify the default settings described above.
Example
This example sets the DHCP Snooping Information circuit-id suboption string.
Console(config)#interface ethernet 1/1
Console(config-if)#ip dhcp snooping information option circuit-id string mv2
Console(config-if)#
ip dhcp snooping trust This command configures the specified interface as trusted. Use the no form to
restore the default setting.
Syntax
[no] ip dhcp snooping trust
Default Setting
All interfaces are untrusted
Command Mode
Interface Configuration (Ethernet, Port Channel)
Command Usage
◆ A trusted interface is an interface that is configured to receive only messages
from within the network. An untrusted interface is an interface that is
configured to receive messages from outside the network or fire wall.
◆ Set all ports connected to DHCP servers within the local network or fire wall to
trusted, and all other ports outside the local network or fire wall to untrusted.
◆ When DHCP snooping is enabled globally using the ip dhcp snooping
command, and enabled on a VLAN with ip dhcp snooping vlan command,
DHCP packet filtering will be performed on any untrusted ports within the
VLAN according to the default status, or as specifically configured for an
interface with the no ip dhcp snooping trust command.
◆ When an untrusted port is changed to a trusted port, all the dynamic DHCP
snooping bindings associated with this port are removed.
◆ Additional considerations when the switch itself is a DHCP client – The port(s)
through which it submits a client request to the DHCP server must be
configured as trusted.