This document discusses network security and firewalls. It explains that network security aims to create a secure computing platform and protect systems from hackers through devices like firewalls. Firewalls examine incoming and outgoing messages on a network and block those that do not meet security criteria. They can filter network traffic using packet filtering, proxy services, or stateful inspection. Firewalls are customizable and can filter based on IP addresses, domains, protocols, and other conditions to control network access and traffic flow.

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2. Network is medium for communication Security has become a mandatory thing for every network Network security can be described as the effort to create a secure computing platform Network Security systems insure the integrity of the system by protecting from hackers Network security can be provided through secure network devices like firewalls .

3. Network security can be described as the effort to create a secure computing platform Network Security systems insure the integrity of the system by protecting from hackers Network security can be provided through secure network devices like firewalls By this network security agents (users or programs) cannot perform actions that they are not allowed to perform, but can perform the actions that they are allowed to.

4. Firewalls is a combination of both hardware and software, means it can be implemented in both hardware and software Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet. All messages entering or leaving the internet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria. A firewall can use one or more sets of `rules’ to inspect the network packets as they come in or go out of your network connections

6. To protect and insulate the applications, services and machines of your internal network from unwanted traffic coming in from the public Internet. To limit or disable access from hosts of the internal network to services of the public Internet. To support network address translation (NAT), which allows your internal network to use private IP addresses and share a single connection to the public Internet A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system.

7. Firewalls use one or more of following three methods to control traffic flowing in and out of the network Packet filtering : 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.

8. Firewalls are customizable. This means that you can add or remove filters based on several conditions. Some of these are: IP addresses : Each machine on the Internet is assigned a unique address called an IP address. Domain names : IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names Protocols : The protocol is the pre-defined way that someone who wants to use a service talks with that service , Some common protocols that you can set firewall filters for include: IP (Internet Protocol) - the main delivery system for information over the Internet TCP ( Transmission Control Protocol ) - used to break apart and rebuild information that travels over the Internet HTTP ( Hyper Text Transfer Protocol ) - used for Web pages

9. FTP (File Transfer Protocol ) - used to download and upload files UDP ( User Datagram Protocol ) - used for information that requires no response, such as streaming audio and video ICMP ( Internet Control Message Protocol ) - used by a router to exchange the information with other routers SMTP ( Simple Mail Transport Protocol ) - used to send text-based information (e-mail) SNMP ( Simple Network Management Protocol ) - used to collect system information from a remote computer Telnet - used to perform commands on a remote computer

10. Remote login Application backdoors SMTP session hijacking Operating system bugs Redirect bombs Source routing

11. Proxy Servers : A function that is often combined with a firewall is a proxy server The proxy server is used to access Web pages by the other computers When another computer requests a Web page, it is retrieved by the proxy server and then sent to the requesting computer If you access a page on a Web site, it is cached (stored) on the proxy server. This means that the next time you go back to that page, it normally doesn't have to load again from the Web site. D.M.Z DMZ (Demilitarized Zone). Although this sounds pretty serious, it really is just an area that is outside the firewall.

12. Everyone has a different idea of what “security” is, and what levels of risk are acceptable . Many people pay great amounts of lip service to security, but do not want to be bothered with it when it gets in their way It's important to build systems and networks in such a way that the user is not constantly reminded of the security system around him It's important to get their feedback to understand what can be improved, and it's important to let them know Security is everybody's business, and only with everyone's cooperation, an intelligent policy, and consistent practices, will it be achievable.

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