“I know internet”

Me : I want to visit “http://secuaed.blogspot.in/2012/12/naughty-css-injection-how-bad-it-is.html”

Browser(Friend) : Ok. Let me apply my trick and get back to you with the resource you are looking for.

Browser To Name Server: Can you translate the server name to IP Address(DNS Does This!) ??I need the IP ?

Name Server: Ok Translated and Take the IP. “123.123.234.55”

[Browser Connected to the IP]

Browser to Server(Via IP): I have sent you a “GET” request . Did you see that ? Actually I need

“naughty-css-injection-how-bad-it-is.html ” file.

Server: Take The file.

Summary:

1. Person typed the URL
2. Browser get the URL and Broke it to 3 parts and read the server name.
3. Communicated with the DNS server to get the IP address.
4. Connected to the IP using a Port no.
5. Sent a GET Request
6. Got the file as a response.

Firewalls:

Say we have a company having 500 people. How should we implement Firewall ??

“Out of the 500 computers inside this company, only one of them is permitted to receive public FTP traffic. Allow FTP connections only to that one computer and prevent them on all others. ”

In Simple words Firewall stop connecting to all 500 systems.

Firewalls use one or more of three methods to control traffic flowing in and out of the network:

• Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.
• Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.
• Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.
  

For example, if a certain IP address outside the company is reading too many files from a server, the firewall can block all traffic to or from that IP address.

Firewall vs Proxy Servers

Firewalls can block ports and programs that try to gain unauthorized access to your computer, while proxy servers basically hide your internal network from the Internet. It works as a firewall in the sense that it blocks your network from being exposed to the Internet by redirecting Web requests when necessary. 

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