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1 A firewall is a mechanism for maintaining control over the traffic that flows into and out of our network(s).
2 The concept and first implementations of firewall technologies can be traced back to the late 1980s and early 1990s.
3 A firewall is typically placed in a network where we see the level of trust change.
4 Many of the firewalls in use today are based on the concept of examining the packets that are coming in over the network.
5 examination determines what should be allowed in or out.
6 Packet filtering is one of the oldest and simplest of firewall technologies. Packet filtering looks at the contents of each packet in the traffic individually and makes a gross determination, based on the source and destination IP addresses, the port number, and the protocol being used, of whether the traffic will be allowed to pass. Since each packet is examined individually and not in concert with the rest of the packets comprising the content of the traffic, it can be possible to slip attacks through this type of firewall.
7 Packet filtering looks at the contents of each packet in the traffic individually and makes a gross determination, based on the source and destination IP addresses, the port number, and the protocol being used, of whether the traffic will be allowed to pass.
8 Stateful packet inspection firewalls (generally referred to as stateful firewalls) function on the same general principle as packet filtering firewalls, but they are able to keep track of the traffic at a granular level.
9 packet filtering firewalls and stateful firewalls can only look at the structure of the network traffic itself in order to filter out attacks and undesirable content, deep packet inspection firewalls can actually reassemble the contents of the traffic to look at what will be delivered to the application for which it is ultimately destined.
10 this technology has great promise for blocking a large number of the attacks we might see, the question of privacy is also raised. In theory, someone in control of a deep packet inspection device could read every one of our e-mail messages, see every Web page exactly as we saw it, and easily listen in on our instant messaging conversations.
11 Proxy servers can serve as a choke point in order to allow us to filter traffic for attacks or undesirable content such as malware or traffic to Web sites hosting adult content. They also allow us to log the traffic that goes through them for later inspection, and they serve to provide a layer of security for the devices behind them, by serving as a single source for requests.
12 Proxy servers are nearly ubiquitous in the business world, largely due to the filtering capability they provide. Many companies rely on them to keep the large amounts of spam that flow over e-mail from reaching their users and lowering productivity. We also see them used to filter Web traffic in such environments in order to keep employees from visiting Web sites that might have objectionable material, and to filter out traffic that might indicate the presence of malware.


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1 to ensure, Web
2 restrict, DMZ
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