ECS4660-28F_Management Guide-R03

C HAPTER 29 | General Security Measures
DHCPv4 Snooping
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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 4500
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.