SYN flooding is the most used and deadly DOS/DDOS attacks.
There is not solution for this kind of attack, because even if some protective application (i.e. firewall), detected those packets, and stopped them before entering the LAN, those packets consumed part or most of the corporate bandwidth. (and the protective application resources as well)
How does it work
Computer A sends computer B a legal SYN packet (beginning of the three way handshake), but it spoofs the source IP.
Computer B sends a SYN+ACK packet back to the spoofed IP.
Computer A user needs to make sure that no computer answers on the spoofed IP.
Computer B waits for an answer but it will never come, meanwhile it needs to keep information on that connection attempt (takes up resources), and only after a certain timeout it will free those resources.
Instead of only one packet, Computer A sends the thousands and hundred of thousands of packets (and maybe from multiple computers), this attack takes the resources of the network and the target computer, disallowing legit users to access it.