  The challenging number is used for the detection of Spoofing attack. The IP
Spoofing is considered to be one of the potentially brutal attack which acts as
a tool for the DDoS attack which is considered to be a major threat among
security problems in today's internet. These kinds of attack are extremely
severe. They bring down business of company drastically. DDoS attack can easily
exhaust the computing and communication resources of its victim within a short
period of time. There are attacks exploiting some vulnerability or
implementation bug in the software implementation of a service to bring that
down and some attacks will use all the available resources at the target
machine. This deals on attacks that consume all the bandwidth available to the
victim machine. While concentrating on the bandwidth attack the TCP SYN flood
is the more prominent attack. TCP/IP protocol suite is the most widely used
protocol suite for data communication. The TCP SYN flood works by exhausting
the TCP connection queue of the host and thus denying legitimate connection
request. There are various methods used to detect and prevent this attack, one
of which is to block the packet based on SYN flag count from the same IP
address. This kind of prevention methods becomes unsuitable when the attackers
use the Spoofed IP address. The SYN spoofing becomes a major tool the TCP SYN
flooding. For the prevention of this kind of attacks, the TCP specific probing
is used in the proposed scheme where the client is requested challenging number
while sending the ACK in the three way hand shake. This is very useful to find
the Spoofed IP Packets/TCP SYN flood and preventing them.
