IP address spoofing

In computer networking, IP address spoofing or IP spoofing is the creation of (IP) packets with a false source IP address, for the purpose of hiding the identity of the sender or impersonating another computing system. One technique which a sender may use to maintain anonymity is to use a proxy server.

The basic protocol for sending data over the Internet network and many other computer networks is the (IP). The protocol specifies that each IP packet must have a header which contains, among other things, the IP address of the sender of the packet. The source IP address is normally the address that the packet was sent from, but the sender's address in the header can be altered, so that to the recipient it appears that the packet came from another source. The protocol requires the receiving computer to send back a response to the source address, so that spoofing is mainly used when the sender can anticipate the network response or does not care about the response.

IP spoofing involving the use of a trusted IP address can be used by network intruders to overcome network security measures, such as authentication based on IP addresses. This type of attack is most effective where trust relationships exist between machines. For example, it is common on some corporate networks to have internal systems trust each other, so that users can log in without a username or password provided they are connecting from another machine on the internal network (and so must already be logged in). By spoofing a connection from a trusted machine, an attacker on the same network may be able to access the target machine without authentication.

IP spoofing is most frequently used in denial-of-service attacks, where the objective is to flood the target with an overwhelming volume of traffic, and the attacker does not care about receiving responses to the attack packets. Packets with spoofed IP addresses are more difficult to filter since each spoofed packet appears to come from a different address, and they hide the true source of the attack. Denial of service attacks that use spoofing typically randomly choose addresses from the entire IP address space, though more sophisticated spoofing mechanisms might avoid unroutable addresses or unused portions of the IP address space. The proliferation of large botnets makes spoofing less important in denial of service attacks, but attackers typically have spoofing available as a tool, if they want to use it, so defenses against denial-of-service attacks that rely on the validity of the source IP address in attack packets might have trouble with spoofed packets. Backscatter, a technique used to observe denial-of-service attack activity in the Internet, relies on attackers' use of IP spoofing for its effectiveness.

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