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FIREWALL

Kriptografi & Keamanan Jaringan

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Introduction to Firewalls

A firewall is a security mechanism to protect a localnetwork from the threats that the network might face

while interacting with other networks.

A firewall can be a hardware component, a software

component, or a combination of both.

It prevents the computers within one network domain

from communicating directly with the computers in

another network domain.

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The main purpose of a firewall is to protect thecomputers of an organization from unauthorized

access.

It allows the authorized users of the local network full

access to the Internet.

The basic functions that are performed by firewalls

are:

Security

Auditing

User authentication

Network Address Translation (NAT)

IP masquerading

Functions of a Firewall

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Security Firewalls prevent unwanted data from getting into the local

network from the Internet or from any other externalnetworks.

It examines the incoming data packets and allows them toenter the local network only if certain conditions are met.

Auditing Firewalls can be used to log the network traffic passing

through it.

This function is useful to track and filter unwantedinformation from entering the network.

Functions of a Firewall (Contd.)

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User authentication In order to provide security to a network, it is essential for a

firewall system to ensure that the users who access theinternal network are authorized.

A firewall system can implement user authenticationprocess in various ways such as using the user id and

password mechanism. Network Address Translation (NAT)

A firewall can be used for hiding the structure and contentsof a local network from external users.

NAT protects the internal private network of an organization

from the Internet by concealing the internal networkaddresses.

Functions of a Firewall (Contd.)

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NAT Implementation by a Firewall

Functions of a Firewall (Contd.)

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IP masquerading is the feature in which the clientnetwork uses a single network interface to interact

with the server.

Implementation of IP Masquerading

Functions of a Firewall (Contd.)

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The working of a firewall is based on a filteringmechanism.

The filtering mechanism of firewalls keeps track ofthe following details:

The source address of the data The destination address of the data

The data contents

The filtering mechanism allows information to bepassed to the Internet from a local network without

requiring any authentication. It makes sure that the downloading of information

from the Internet to a local network happens basedonly on a request made by an authorized user.

Working Principle of Firewalls

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Firewall in a Local Network

Working Principle of Firewalls (Contd.)

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Before using a firewall, the user should know some ofthe following basic terms associated with a firewall:

Gateway

Proxy servers

Screening routers Application-level gateway

Demilitarized zone

Bastion host

Firewall Terminology

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Gateway The computer that helps to establish a connection between

two networks is known as a gateway.

A firewall gateway can be used for exchanging information

between an internal network and the Internet.

Proxy servers

A proxy server masks the networks IP address with the

proxy servers IP address

Firewall Terminology (Contd.)

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Screening routers A screening router is one of the simplest and most effective

defensive mechanisms used in the creation of a firewall

system.

They are a special type of routers with filters, which are used

along with various firewalls.

Application-level gateway

This type of gateway uses a more complex policy than a

packet filtering technique that involves selectively restricting

the data that is allowed through the firewall.

Firewall Terminology (Contd.)

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Application Gateway Between Destination and Source Host

Firewall Terminology (Contd.)

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A demilitarized zone is a subnet between the Internetand the internal network.

An Application Server in a Demilitarized Zone

Firewall Terminology (Contd.)

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Bastion host

A bastion host is a publicly accessible server that is hosted

on the DMZ.

The bastion host is configured to serve a specific role of

disabling or removing all the protocols, files, and applications

that are not essential to the system.

Firewall Terminology (Contd.)

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Firewall architecture deals with the design of the

firewall system and its components and is

implemented in a network.

The following are the different types of firewallarchitectures:

Dial-up architecture

Single router architecture

Firewall with proxy server

Firewall Architecture

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Dial-up architecture It uses a dial-up service, such as an ISDN line.

A firewall system is used to separate the Internet from thelocal network.

Dial-up Architecture

Firewall Architecture (Contd.)

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Single router architecture You use a router to access the Internet.

Single Router Architecture

Firewall Architecture (Contd.)

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A firewall with a proxy server

Firewalls with a proxy server are used in a small network.

Here, the firewall system is integrated with your proxy

server.

These Firewalls can be implemented in two ways:

A firewall with built-in proxy services A firewall with a proxy server product installed separately

Firewall Architecture (Contd.)

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Firewall with proxy server

Firewall with Built-in Proxy Services

Firewall Architecture (Contd.)

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Firewall with proxy server

Firewall with a Proxy Server Product Installed Separately

Firewall Architecture (Contd.)

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The type of firewall used might vary from network to

network.

The following are the various types of firewalls

generally used:

Packet filter firewall

Circuit-level firewall

Proxy firewall

Network Address Translation (NAT) firewall

Types of Firewalls

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Packet filter firewall

Are usually deployed on routers.

Is the simplest and the primary defensive mechanism used

in firewall protection.

Are implemented at the network level to check all incoming

and outgoing packets of information.

Types of Firewalls (Contd.)

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Circuit-level firewall

Provides more protection than packet filtering firewalls.

Also known as a stateful inspection firewalls.

Checks for all the connections made to the local network.

Types of Firewalls (Contd.)

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Proxy firewall

Protects all the client applications running on a network from

the Internet by using the firewall itself as a gateway.

Automatically segregates the data packets depending upon

the protocols used by them.

Must support various protocols.

Types of Firewalls (Contd.)

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Network Address Translation firewall

Use a single IP address to represent the network.

All packets going outside the network have their internal IP

addresses hidden from the outside to increase security.

Any incoming packets are delivered only to the networks

public IP address.

Types of Firewalls (Contd.)

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A firewall can be used for securing the applications

running on a local network from the Internet.

It allows to use Internet services such as e-mail and

messengers from inside the protected network.

The idea behind the use of firewalls is to allow only

secured applications or services to pass through the

network and stop unsecured applications from

entering the network.

Role of Firewalls in Application Security

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Using Firewalls in VPNs

VPN guarantees private secured network traffic to

organizations.

Firewalls can be used with VPNs to enhance network

security.

The following figure shows the implementation of firewallswith VPNs:

Role of Firewalls in Application Security (Contd.)

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An organization can use a software firewall or a

hardware firewall or a mixture of both for network

security.

The firewalls solutions are:

Software firewall

Hardware firewall

Firewall Solutions

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Software firewall Works on a computer system. Software firewalls provide the

following benefits: They are inexpensive.

They can be easily configured.

Has the following disadvantages: The software firewall consumes disk, memory, and CPU

resources on your computer. Software firewalls may affect the performance of the operating

system.

The security threats to an operating system can affect theperformance of the software firewalls.

Examples include the DoorStop firewall and SINUS.

Firewall Solutions (Contd.)

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Has the following advantages:

The level of network protection is high.

They can support more network interfaces than most software

firewalls.

The performance of a hardware firewall exceeds software

firewalls because it does not have any additional overhead

found in operating systems. Has the following disadvantage:

Are very expensive compared to software firewalls.

Example includes SonicWall.

Firewall Solutions (Contd.)