SYN Flood is a DOS attack in which an attacker deliberately violates the three-way handshake and opens a large number of half-open TCP connections. The signature of attack for SYN Flood contains:

A.
The source and destination port numbers having the same value

B.
A large number of SYN packets appearing on a network with the corresponding reply packets

C.
A large number of SYN packets appearing on a network without the corresponding reply packets

D.
The source and destination address having the same value

Explanation:
A SYN attack occurs when an attacker exploits the use of the buffer space during a Transmission Control Protocol (TCP) session initialization handshake. The attacker floods the target system’s small "in-process" queue with connection requests, but it does not respond when a target system replies to those requests. This causes the target system to time out while waiting for the proper response, which makes the system crash or become unusable.