What is a network firewall, and what can a firewall protect my systems against?
A firewall is a system that enforces an access control policy between two networks. In general, a firewall is used to block network traffic coming from outside the network to the inside, and permit traffic from the inside to communicate to the outside world. A firewall can also provide logging and auditing functions to record all traffic passing through. In other words, a firewall can protect the internal network against attacks from outside by defining an access control policy to permit or deny traffic. However, a firewall cannot protect against attacks that do not go through the firewall itself, and cannot protect against attacks like viruses or data driven attacks that ride inside network traffic permitted by the firewall (such as web traffic). Proper configuration of a firewall plays a very important role in ensuring its effectiveness in terms of security protection.
