IP address spoofing is a type of attack when an attacker assumes the source Internet Protocol (IP) address of IP packets to make it appear as though the packet is coming from another valid IP address. In IP address spoofing, IP packets are generated with fake source IP addresses in order to impersonate other systems or to protect the identity of the sender.
To explain this clearly, in IP address spoofing, the IP address information placed on the source field of the IP header is not the real IP address of the source computer, where the packet was originated. By changing the source IP address, the actual sender can make it look like the packet was sent by another computer and therefore the response from the target computer will be sent to the fake address specified in the packet and the identity of tha attacker is also protected.
Packet filtering is a method to prevent IP spoofing attacks. Blocking of packets from outside the network with a source address inside the network (ingress filtering) and blocking of packets from inside the network with a source address outside the network (egress filtering) can help preventing IP spoofing attacks.