Bob has finally had enough of Malice's behavior and has sought your help to set up a firewall with packet filtering to stop the malicious packets entering his network from Malice's computers that are hosted on a different local area network. Bob is aware of the IP addresses of the computers Malice uses

I need help to briefly explain how you would design a firewall (You can describe it in text. It need not be in any firewall product format) to help Bob to prevent Malice from launching a SYN flood attack against a host within Bob's network.

For example, think about a rule of the form "block all packets with value x in the field y".

Please cite all used sources and no copy paste answers.