IP spoofing involves an attacker using a spoofed IP address to gain access to information or systems. There are several types of attacks that use IP spoofing, including blind spoofing where the attacker does not see return packets, man-in-the-middle attacks by intercepting traffic, and source routing attacks where the attacker specifies their system is in the packet route. Defenses include not relying on IP-based authentication, using router filters to block spoofed packets, and using random sequence numbers to prevent prediction. While less common now, application spoofing remains a threat if programs are not properly configured.