The Cisco switch must be configured to have gratuitous ARP disabled on all external interfaces.
A gratuitous ARP is an ARP broadcast in which the source and destination MAC addresses are the same. It is used to inform the network about a host IP address. A spoofed gratuitous ARP message can cause network mapping information to be stored incorrectly, causing network malfunction.
Disable gratuitous ARP as shown in the example below: SW1(config)#no ip gratuitous-arps
Review the configuration to determine if gratuitous ARP is disabled. The following command should not be found in the switch configuration: ip gratuitous-arps Note: With Cisco IOS, gratuitous ARP is enabled and disabled globally. If gratuitous ARP is enabled on any external interface, this is a finding.