The recommended action to mitigate an attack that is broadcasting a large number of ICMP packets using a spoofed source IP address is to use the subinterface command no ip directed-broadcast. This command prevents the Cisco IOS device from forwarding packets that are addressed to IP broadcast addresses. By disabling the directed broadcast feature, the network devices will not respond to broadcast messages sent to the network's broadcast address, thus mitigating the attack and preventing the amplification of the ICMP packets back to the victim's IP address.