Firewalls
Broda M Broadus
ECPI University

A firewall can either be software-based or hardware-based and is used to help keep a network secure. Its primary objective is to control the incoming and outgoing network traffic by analyzing the data packets and determining whether it should be allowed through or not, based on a predetermined rule set. A network's firewall builds a bridge between the internal network or computer it protects, upon securing that the other network is secure and trusted, usually an external (inter)network, such as the Internet, that is not assumed to be secure and trusted.
Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic routing functions.
Although Firewalls have been good in the past for protection with the growing DDoS attacks it’s hard for them to work effectively in certain cases. Firewalls should not be placed in front of servers. Folks do it because they have been programmed to do it. In many cases, these devices became immediate bottlenecks in the face of DDoS, achieving the attackers' aims with ease.
Firewalls and IPS were fine for LANs where they filtered outgoing traffic, but turned into obvious points of failure when used as a barrier to protect servers receiving large volumes of inbound packets. Firewalls are an important part of any network setup but if you put them in front of your Web servers, they become a single point of failure in the event of a DDoS attack. If you look at the big picture firewalls work but since they only cover one way in and one way out that’s easy for certain attacks to penetrate. This is what makes DDoS so easy to attack the firewall.

Citations
Ingham, Kenneth; Forrest, Stephanie (2002). "A History and Survey of Network Firewalls" . p. 4. Retrieved 2013-4-9