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Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 20 Configuring DHCP Features and IP Source Guard Features
Configuring IP Source Guard
• If you enable IP source guard with source IP and MAC address filtering, DHCP snooping and port
security must be enabled on the interface. You must also enter the ip dhcp snooping information
option global configuration command and ensure that the DHCP server supports option 82. When
IP source guard is enabled with MAC address filtering, the DHCP host MAC address is not lea rned
until the host is granted a lease. When forwarding packets from the server to the host, DHCP
snooping uses option-82 data to identify the host port.
• When configuring IP source guard on interfaces on which a private VLAN is configured, port
security is not supported.
• IP source guard is not supported on EtherChannels.
• You can enable this feature when 802.1x port-based authentication is enabled.
• If the number of ternary content addressa ble memory (TCAM) entries exceeds the maximu m, the
CPU usage increases.
• In a switch stack, if IP source guard is configured on a stack member interface and you remove the
switch configuration by entering the no switch stack-member-number provision global
configuration command, the interface static bindings are removed from the binding table. They are
not removed from the running configuration. If you again provision the switch by entering the
switch stack-member-number provision command, the binding is restored. To remove the binding
from the running configuration, you must disable IP source guard before entering the no switch
provision global configuration command. The configuration is also removed if the switch reloads
while the interface is removed from the binding table. For more information about provisioned
switches, see the “Stack Offline Configuration” section on page 7-7.
Enabling IP Source Guard
Begin in privileged EXEC mode.
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 interface interface-id Specify the interface to be configured, and enter interface configuration
mode.
Step 3 ip verify source
or
ip verify source port-security
Enable IP source guard with source IP address filtering.
Enable IP source guard with source IP and MAC address filtering.
Note When you enable both IP source guard and Port Security by using
the ip verify source port-security interface configuration
command, there are two caveats:
• The DHCP server must support option 82, or the client is not
assigned an IP address.
• The MAC address in the DHCP packet is not learned as a secure
address. The MAC address of the DHCP client is learned as a
secure address only when the switch receives non-DHCP data
traffic.
Step 4 exit Return to global configuration mode.