In the Cisco ASA firewall appliance provides more protection outside the box with the default configuration. However, in order to increase the protection of another, there are several configuration accessories that can be used to implement additional security features. Two of these features are IP Spoofing protection and basic Intrusion Prevention (IPS) support.
IP Spoofing Protection
IP spoofing attacks are those that change the actual IP-address of the source package to hide their true origin. This means that packets arriving at the particular interface (eg, inside) must have a valid source IP address, which coincides with the correct source interface according to the firewall in the routing table. Typically, a firewall only looks at the packet destination address, in order to direct it accordingly. If you enable IP Spoofing mechanism, the firewall also checks the source address packets.
For example, if our internal interface for connecting to the internal network of 192.168.1.0/24, which means that packets arrive at the internal interface of the firewall must be addressed in the range 192.168.1.0/24 or they will be reset (if configured IP Spoofing).
IP-Spoofing is used Unicast Reverse path Forwarding (Unicast RPF) mechanism, which dictates that for any traffic that you want to allow through the security device, security device in the routing table must include a route back to the original address.
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