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Four major types of firewalls in OSI2

Window firewalls3

Firewall

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An internetwork gateway that restricts data communicationtraffic to and from one of the connected networks (the onesaid to be "inside" the firewall) and thus protects that

network's system resources against threats from the othernetwork (the one that is said to be "outside" the firewall).

A firewall is hardware, software, or a combination of boththat is used to prevent unauthorized programs or Internetusers from accessing a private network and/or a singlecomputer

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Hardware Firewalls

Protect an entire network

Implemented on the router level

Usually more expensive, harder to configure

Software Firewalls

Protect a single / group of computers Usually less expensive, easier to configure

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Intranet

DMZInternet

Firewall

Firewall

Web server, email

server, web proxy,etc

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DeMilitarized Zone: a portion of a networkthat separate a purely internal network from

an external network.

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Allow traffic that flows automaticallybecause it has been deemed as safe (Ex.

Meeting Maker, Eudora, etc.) Block traffic that is blocked because it has

been deemed dangerous to your computer Ask asks the user whether or not the traffic

is allowed to pass through

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Packet filters

work at the network level.

compared to a set of criteria before it is forwarded

Advantages: low cost, low impact on networkperformance.

Disadvantages: does not support sophisticated rulebased models.

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Circuit level gateways work at the session layer

monitor TCP handshaking between packets to

determine whether a requested session is legitimate Information passed to remote computer through a

circuit level gateway appears to have originated fromthe gateway.

Advantages: relatively inexpensive , hidinginformation about the private network Disadvantages:they do not filter individual packets.

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Application level gateways

work at the application layer

Incoming or outgoing packets cannot access servicesfor which there is no proxy

filter application specific commands

can also be used to log user activity and logins.

Advantages: a high level of security Disadvantages: having a significant impact on network

performance, not transparent to end users.

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Stateful multilayer inspection firewalls work at the application , session, network layer.

They filter packets at the network layer, determinewhether session packets are legitimate and evaluatecontents of packets at the application layer

They allow direct connection between client and host,alleviating the problem caused by the lack oftransparency of application level gateways. can alsobe used to log user activity and logins.

Advantages: a high level of security, goodperformance, transparency to end users

Disadvantages: they are expensive and complex.

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In 2003, Sasser worm and blaster wormattacked a large number of Windows machines,taking advantage of flaws in the RPC Windowsservice. Adding to that, Microsoft was criticizedfor not being active in protecting customersfrom threats. Therefore, Microsoft decided toimprove both functionality and the interface ofWindows XPs built-in firewall, and rebrand itas: Windows Firewall.

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Windows Firewall helps protecting yourcomputer by preventing unauthorized users

from gaining access to your computerthrough a network or internet.

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Help block computer viruses and wormsfrom reaching your computer.

Ask for your permission to block or unblockcertain connection requests.

Create a record (a security log)

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