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4
Command Line Interface
• When DHCP snooping is globally enabled, configuration changes for specific
VLANs have the following effects:
- If DHCP snooping is disabled on a VLAN, all dynamic bindings learned for
this VLAN are removed from the binding table.
Example
This example enables DHCP snooping for VLAN 1.
Console(config)#ip dhcp snooping vlan 1
Console(config)#
Related Command
ip dhcp snooping (4-115)
ip dhcp snooping trust (4-118)
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 firewall.
• Set all ports connected to DHCP servers within the local network or firewall to
trusted, and all other ports outside the local network or firewall to untrusted.
• When DHCP snooping enabled globally using the ip dhcp snooping
command (page 4-115), and enabled on a VLAN with ip dhcp snooping vlan
command (page 4-117), 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.
4-118