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DHCP S
NOOPING
C
OMMANDS
22-11
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 ip dhcp
snooping vlan command (page 22-13), DHCP messages received on
an untrusted interface (as specified by the no ip dhcp snooping trust
command, page 22-17) 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, and
static entries configured in the DHCP snooping table.
• Table entries are only learned for untrusted interfaces. Each entry
includes a MAC address, IP address, lease time, entry type
(Dynamic-DHCP-Binding, Static-DHCP-Binding), 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 the global DHCP snooping is disabled, all DHCP packets are
forwarded.