The Juniper router 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.

Review the configuration to determine if gratuitous ARP is disabled on all external interfaces. [edit interfaces] <external interface> { no-gratuitous-arp-reply; no-gratuitous-arp-request; unit <number> { family inet { address <IPv4 address>/<mask>; } family inet6 { address <IPv6 address>/<mask>; } } }

If gratuitous ARP is enabled on any external interface, this is a finding.

Disable gratuitous ARP on all external interfaces.

set interfaces <external interface> no-gratuitous-arp-reply set interfaces <external interface> no-gratuitous-arp-request set interfaces <external interface> unit <number> family inet address <IPv4 address>/<mask> set interfaces <external interface> unit <number> family inet6 address <IPv6 address>/<prefix>