Which option is the cause of the problem?

A switch is added into the production network to increase port capacity. A network engineer is configuring the switch for DHCP snooping and IP Source Guard, but is unable to configure ip verify source under several of the interfaces.

Which option is the cause of the problem?
A . The local DHCP server is disabled prior to enabling IP Source Guard.
B . The interfaces are configured as Layer 3 using the no switchport command.
C . No VLANs exist on the switch and/or the switch is configured in VTP transparent mode.
D . The switch is configured for sdm prefer routing as the switched database management template.
E . The configured SVIs on the switch have been removed for the associated interfaces.

View Answer

Answer: B

Explanation:

IP source guard is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering traffic based on the DHCP snooping binding database and on manually configured IP source bindings. You can use IP source guard to prevent traffic attacks caused when a host tries to use the IP address of its neighbor. You can enable IP source guard when DHCP snooping is enabled on an untrusted interface. After IP source guard is enabled on an interface, the switch blocks all IP traffic received on the interface, except for DHCP packets allowed by DHCP snooping. A port access control list (ACL) is applied to the interface. The port ACL allows only IP traffic with a source IP address in the IP source binding table and denies all other traffic. The IP source binding table has bindings that are learned by DHCP snooping or are manually configured (static IP source bindings). An entry in this table has an IP address, its associated MAC address, and its associated VLAN number. The switch uses the IP source binding table only when IP source guard is enabled. IP source guard is supported only on Layer 2 ports, including access and trunk ports. You can configure IP source guard with source IP address filtering or with source IP and MAC address filtering.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12­2_25_see/configuration/guide/3550SCG/ swdhcp82.html#wp1069615