Firewall is one of the great features that can be incorporated in your system for analyzing incoming and outgoing traffic. Based on this, they are capable to take an appropriate action. Also, they can perform several conditional evaluations.
These conditional evaluations are also referred to as 'rules'. When a firewall is constructed, it is set with rules that will be strictly followed by it. For example, if the company policy demands that only the sales department will have the access to the FTP site, the firewall can be set accordingly.

Read More So, even if any other department wants to access the site, it will not be possible. In this aspect, Firewalls are to networks what privilege schemes are to operating systems. For example, Windows XP will allow you to specify which users can access a directory or a file. In a similar way, firewalls can provide you with access control to your web sites or network work stations.
Some other features included in firewall are as follows:
a) Virtual Private Networking:
They are also referred to as VPN's. VPN's are used to move the traffic securely from point A to point B over the internet. it creates a tunnel between the points separating the private traffic from the public. There are many players both commercial and open source in the open market offering these services. Many firewall dedicated products offer both LAN-to-LAN and VPN functionalities.
b) Load Balancing:
It's more of a generic term and it refers to the art of moving the traffic in a distributed way. To minimize link congestion this done by routing traffic through two different tunnels they maybe from different internet service providers. These days, some firewalls products also incorporate certain features like directing FTP traffic and web in a distributed manner.
c) Content filtering:
Companies may want to block their employees from viewing certain websites like: underground sites, pornography sites, and web based emails to either reduce on the running costs in terms of bandwidth, maintainous costs etc Content filtering features in a firewall allows you to do just that. It blocks all the sites other than the specified ones.
d) Network Address Translation:
Firewalls allow you to bind one ip to hundreds allowing the outside world on the web to see your network as one it protects your internal users and servers from the web minimizing the hacker’s risk they are often used to map illegal address blocks to valid ones. NAT's are security related, devices that make use of them in corporate world are firewall products.

e) Intrusion Detection:
They detect unwanted attempts at accessing, manipulating, and/or disabling of computer systems, mainly through a network In general, this term could mean anything. But in this context, some manufacturers are beginning to combine different types of products into their firewall offering. Even though this in itself doesn't create a problem, users have to be a bit weary of the work load that might be imposed on their firewal

f) Fault tolerance:
Few higher end firewall products developed by companies like Nokia/Checkpoint combination and Cisco PIX support certain kind of fail-over features.
Fault tolerance features of firewall products are also referred to as High-Availability functionality. Advanced versions of fault tolerance features allow the firewalls to run in pairs. In this scenario, while one device is functioning, the other will act as a stand by.
Entertaining the thoughts of managing all these features in one single product, can be a daunting task. Hence, one has to approach it with a kitchen sink mentality and with a fair amount of skepticism. Let us not forget that they have a played a pivotal role in various security models of different organizations as well.