General Security Measures
4-165
4
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
firewall. When DHCP snooping is enabled globally by this command, and
enabled on a VLAN interface by the
command
(page 4-167), DHCP messages received on an untrusted interface (as
specified by the
command, page 4-167) 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 untrusted interfaces. Each entry includes a
MAC address, IP address, lease time, VLAN identifier, and port identifier.
• When DHCP snooping is enabled, the rate limit for the number of DHCP
messages that can be processed by the switch is 100 packets per second.
Any DHCP packets in excess of this limit are dropped.
• Filtering rules are implemented as follows:
- If global DHCP snooping is disabled, all DHCP packets are forwarded.
- If DHCP snooping is enabled globally, and also enabled on the VLAN where
the DHCP packet is received, all DHCP packets are forwarded for a
trusted
ip dhcp snooping
information policy
Sets the information option policy for DHCP client packets that
include Option 82 information
GC
ip dhcp snooping
database flash
Writes all dynamically learned snooping entries to flash
memory
PE
clear ip dhcp snooping
database flash
Removes all dynamically learned snooping entries from 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 4-45 DHCP Snooping Commands
(Continued)
Command
Function
Mode
Page
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