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website on the user’s hard disk. The information is stored in the form of name value pair. Generally,
the cookies folder is stored in c:\windows\cookies.
Working of Cookies

1. The user enters the name of the website on the browser.

2. The browser contacts the DNS server to convert the domain name into IP address. The browser
looks for the cookies on the hard disk.
3. The IP address is used to contact the corresponding server along with cookies data.

4. If no cookies data is supplied, then the website comes to know that the user is visiting the
website for the first time.
5. The server creates an ID of a person which is then stored by cookies on the hard disk.

The information which is stored by a website is known as state information. The information can
be of the following types:

1. How many visitors have visited the site?
2. How many are new visitors?

3. How many are repeat visitors?
4. What is the frequency of a particular visitor?

CTM: Cookies are the messages which are stored by the website on a user’s hard disk whenever they visit
any website.

8.24 FIREWALL

A firewall is a software that protects the private network from unauthorized user access. The
firewall filters the information coming from the internet to the network or a computer to protect
the system. Firewall exists both as a software solution and as a hardware application. In the form
of hardware firewall such as router, it protects the network, and in terms of software firewall, it
helps in preventing the spread of virus from one computer to another. A firewall is a network
security system, either hardware- or software-based, that controls incoming and outgoing network
traffic based on a set of rules. Various examples of firewalls are CISCO firewall, NetGear firewall,
Netscreen 25, etc.
A firewall can use various methods for filtering the information such as:

1. Packet filtering: In packet filtering, the data, which is outgoing or incoming in the form of
packets, is filtered. Packet filter looks at each packet entering or leaving the network and accepts
Computer Science with Python–XII 8.46 2. Proxy service: The information which is requested is not directly sent to the person who
or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to
users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.

makes the request; rather, the information is first received in firewall and then sent to the
proxy server. The proxy server intercepts all messages entering and leaving the network and
effectively hides the true network addresses.

3. IP address blocking: If the data is coming from a network or website that contains some
unwanted data, then the data from that particular IP address or domain name is blocked by
firewall.