Problem
Networks receive packets from other networks. Normally a packet will contain the IP address of the computer that originally sent it. This allows devices in the receiving network to know where it came from, allowing a reply to be routed back (amongst other things).
However, a sender IP address can be faked ('spoofed'), characterising a Spoofing attack. This disguises the origin of packets sent, for example in a Denial-of-service attack.
Read more about this topic: Ingress Filtering
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