• IP spoofing is a technique used to gain unauthorized access to computers, where by the attacker send messages to a computer with a foreign IP address indicating that the message is coming from a trusted host.
• Attacker puts an internal, or trusted, IP address as its source. The access control device saw the IP address as it is trusted and then lets it through.
• IP spoofing occurs when a hacker inside or outside a network impersonates the conversations of a trusted computer.

Note : This article is written only for educational purposes. The contents should not be useful for any illegal purposes.

• There are two general techniques are used during IP spoofing:
• A hacker uses an IP address that is within the range of trusted IP addresses.
• A hacker uses an authorized external IP address that is trusted.

• Other uses for IP spoofing:
• IP spoofing is usually limited to the injection of malicious data or commands into an existing stream of data.
• A hacker changes the routing tables to point to the spoofed IP address, then the hacker can receive all the network packets that are addressed to the spoofed address and reply just as any trusted user can.

• Problem with the Routers.
• Routers look at Destination addresses only.
• Authentication based on Source addresses only.
• To change source address field in IP header field is easy.

• There are a few variations on the types of attacks that using IP spoofing.

• This attack takes place when the attacker is on the same subnet as the target that could see sequence and acknowledgement of packets.
• Using this spoofing to interfere with a connection that sends packets along with their own subnet.

• This attack may take place from outside where sequence and acknowledgement numbers are unreachable.
• Attackers usually send several packets to the target machine in order to sample sequence numbers, which is double in older days .
• Using these spoofing to interfere with a connection (or creating one), that does not send packets along with the cable.

• These type is also called as connection hijacking.
• In this attack, a malicious party intercepts a legitimate communication between two hosts to controls the flow of communication and to eliminate or alter the information sent by one of the original participants without their knowledge.

• Send ICMP ping packet with spoofed IP source address to a LAN which will broadcast to all hosts on the LAN.
• Each host will send a reply packet to the spoofed IP address leading to denial of service.

• This is how, the attacker will change the IP Address while doing illegal activity through online.
• Using this kind of techniques, the attackers will hack the servers .