CLI Reference Guide-R07

Chapter 9 | General Security Measures
DHCPv4 Snooping
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ip dhcp snooping This command enables DHCP snooping globally. Use the no form to restore the
default setting.
Syntax
[no] ip dhcp snooping
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
◆ Network traffic may be disrupted when malicious DHCP messages are received
from an outside source. DHCP snooping is used to filter DHCP messages
received on an unsecure interface from outside the network or fire wall. When
DHCP snooping is enabled globally by this command, and enabled on a VLAN
interface by the ip dhcp snooping vlan command, DHCP messages received on
an untrusted interface (as specified by the no ip dhcp snooping trust
command) from a device not listed in the DHCP snooping table will be
dropped.
◆ When enabled, DHCP messages entering an untrusted interface are filtered
based upon dynamic entries learned via DHCP snooping.
◆ Table entries are only learned for trusted interfaces. Each entry includes a MAC
address, IP address, lease time, VLAN identifier, and port identifier.
ip dhcp snooping max-
number
configures the maximum number of DHCP clients which
can be supported per interface
IC
ip dhcp snooping trust Configures the specified interface as trusted IC
ip dhcp snooping information
option circuit-id
Enables or disables the use of DHCP Option 82
information circuit-id suboption
IC
ip dhcp snooping trust Configures the specified interface as trusted IC
clear ip dhcp snooping
binding
Clears DHCP snooping binding table entries from RAM PE
clear ip dhcp snooping
database flash
Removes all dynamically learned snooping entries from
flash memory.
PE
ip dhcp snooping database
flash
Writes all dynamically learned snooping entries to flash
memory
PE
show ip dhcp snooping Shows the DHCP snooping configuration settings PE
show ip dhcp snooping
binding
Shows the DHCP snooping binding table entries PE
Table 57: DHCP Snooping Commands (Continued)
Command Function Mode