With IP Spoofing the sender of a packet poses itself as another computer. This happens either in order to trick the Firewall, which trusts packets from the own network more than packets from untrusted networks, or in order to hide the author of an attack (e.g. Smurf).
The LANCOM Firewall protects itself against spoofing by route examination, i.e. it examines, whether a packet was allowed to be received over a certain interface at all, from which it was received.