In today's world, most business, regardless of size, believe that access to Internet is imperative if they are going to compete effectively. Yet connecting a private computer (or a network) to the Internet can expose critical or confidential data to malicious attack from anywhere in the world since unprotected connections to the Internet (or any network topology) leaves the user computer vulnerable to hacker attacks and other Internet threats. Therefore, to provide protection to the network and network computers, firewall needs to be used. Firewall provides a barrier between the user computer and the Internet (i.e. it prevents unauthorized Internet users from accessing private computers and networks connected to the Internet. This work concerned with development of a proposed Dynamic Packet Filtering Firewall system called (DPFF) which is used to protect both individual computers and corporate networks from hostile intrusion from the LAN. The Screened Host Architecture has been used to implement the proposed system. The designed DPFF is implemented using JAVA language and was tested on a LAN. DPFF absolutely isolates user computer from the other network computers using a wall of code that inspects each individual packet of data as it arrives at either side" of the firewall (inbound to or outbound from user computer) to determine whether it should be allowed to pass or be blocked. The designed firewall is provided with friendly user interface.