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Computer Network Security and Firewalls - 2


DRAWINGS USED IN THE PROJECT


Figure 1.1.1a: General structure of a computer. 14

Figure 1.1.1b: Computer central processing unit (CPU) 15

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Figure 1.1. 1c: Control unit of CPU 16

Figure 1. 1.2: Basic functions of a computer 17

Figure 1.2. 1: Computer network with preprocessor. 18

Figure 1.2.4.3.1: Star network 25

Figure 1.2.4.3.2: Ring network 26

Figure 1.2.4.3.3: Linear backbone network (Bus) 26

Figure 1.2.4.3.4: Radio Network – Satellite or Radio 27

Figure 1.2.4.3.5: Mixed connection network 28

Figure 1.2.5.2: Wide area network with LAN to LAN connection 30

Figure 2.2.2: OSI 7 layer reference model 33

Figure 2. 2.4: Data transmission process in the OSI model 36

Figure 2.3.1.1a: OSI model and TCP/IP architecture model 38

Figure 2.3.1.1.b: Data structure at TCP/IP layers 39

Figure 2.3.1.2.1a: How to type TCP/IP address 40

Figure 2.3.1.2.1b: Adding subnetid 41

Figure 2.3.1.2a: TCP/IP data packet structure 42

Figure 2.3.1.2.2c: TCP service access port 43

Figure 2.3.1.3: Using gateways to send data packets 44


Figure 3.1 Common network diagram today 48

Figure 3.3 Network Security Levels 50

Figure 4.2.a: Stateless Firewall 63

Figure 4.2.b: Stateful Firewall 64

Figure 4.2.c: Deep Packet Layer Firewall 64

Figure 4.2.1a: PIX 65 interface

Figure 4.2.1b: NetScreen Firewall layout. 66

Figure 4.3.1: Dual–homed Host architecture diagram 67

Figure 4.3.2: Screened Host Architecture Diagram 69

Figure 4.3.3: Screened Subnet Host 70 Architecture Diagram

Figure 4.4.1: Working diagram of Packet Filtering 72

Figure 4.4.2: Connection between user (Client) and Server via Proxy 74

Figure 4.4.3: Connection via Circuit–Level Gateway. 77

Figure 5.1.3.1:Overview of Network-Based IDS 80

Figure 5.1.3.1b: Network-Based IDS 80 Architecture

Figure 5.1.3.1c: Network-Based IDS Sensor Layout 81

Figure 5.1.3.2a: Structure of Host Sensor Agent 83

Figure 5.1.3.2b: Host IDS 84 Deployment

Figure 5.2.3.1: Deploying Intrusion Prevention Sensor 88

Figure 5.2.3.2: Access control processing. 93


Abbreviations


ARP Address resolution protocol

ASYN Asychronous

CPU Central Processing Unit

DNS Domain Name System

EDVAC Electronic Discrete Variable Computer

ENIAC Electronic Numerical Integrator And Computer FTP File Transfer Protocol

GAN Global Area Network

HIDS Host-based Instrusion Detection System HIPS Host-based Instrusion Prevension System HTML Hyper Text Markup Language

HTTP Hyper Text Transport Protocol

IP Internet Protocol

ICMP Internet control message protocol IGMP Internet group management protocol ISDN Integrated Services Digital Network IDS Instrusion Detection System

IPS Instrument Prevension System

LAN Local Area Network

MAC Media Access Control

MAN Metropolitan Area Network

NIC Network Interface Card

NIDS Network-based Instrusion Detection System NIPS Network-based Instrusion Prevension System NSF National Science Foundation

RARP Reverse address resolution protocol


RCP Remote Call Procedure

RIP Routing Information Protocol

SH Session Header

SLIP Serial Line Internet Protocol

SMTP Simple Mail Transfer Protocol

SNMP Simple Network Management Protocol RST Reset

SYN Synchronous

TCP Transmission Control Protocol

TFTP Trivial File Transfer Protocol

TTL Time To Live

VER Version

WAN Wide Area Network


PART I: OVERVIEW OF COMPUTER NETWORKS


CHAPTER 1: INTRODUCTION TO COMPUTERS AND COMPUTER NETWORKS

1.1. Computer history

1.1.1. General structure of the computer

A computer is a complex system with millions of basic electronic components. At its simplest, a computer can be viewed as an entity that interacts in some way with its external environment. In general, its relationships with the external environment can be classified as peripheral devices or communication lines.


Figure 1.1.1a: General structure of a computer

The main and most important component of a computer is the Central Processing Unit (CPU): Controls the computer's operations and performs data processing functions.



Figure 1.1.1b: Computer central processing unit (CPU)

CPU is often referred to as the processor. A computer may have one or more of the above components, for example one or more CPUs. In the past, most computers had only one CPU, but recently there has been an increase in the use of multiple CPUs in a single system. The CPU has always been an important object because it is the most complex component of the system. The structure of a CPU consists of the following main components:

- Control unit: Controls the operation of the CPU and thus controls the operation

of computer.

- Arithmetic and Logic Unit (ALU): Performs the data processing functions of the computer.

- Register set: Provides internal storage for CPU.

- Internal CPU interconnection component: Mechanism that provides communication between the control unit

control, ALU and register set.

Among the above mentioned sub-components of the CPU, the control unit plays the most important role. The implementation of this unit leads to a fundamental concept in the manufacture of computer microprocessors. That is the concept of microprogramming. The figure below depicts the internal organization of a control unit with three main components:

- Logic sequencer.


- Decoder and set of control registers.

- Control memory.


Figure 1.1. 1c: CPU control unit

Other components of the computer:

Main memory: Used to store data.

Input and output components: Used to move data between the computer and the environment.

outside field

System interconnect components: Provide communication mechanism between CPU, memory

main and import and export components.

1.1.2. Computer functions

In general, a computer can perform the following four basic functions:

- Data migration.

- Control.

- Data storage.

- Data processing.


Storage

data

Data Migration

Thing

control

Handle

data


Figure 1. 1.2: Basic functions of a computer

Data processing: Computers must be able to process data. Data can be of many types and the scope of processing requirements is also very wide. However, there are only a few basic methods in data processing.

Data storage: Computers also need to be able to store data. Even when the computer is processing data, it still has to temporarily store each time the data is being processed. Therefore, short-term storage is necessary. However, long-term storage is also important for data that needs to be stored on the computer for subsequent updates and searches.

Data movement: The computer must be able to move data between itself and the outside world. This ability is demonstrated through the movement of data between the computer and devices directly or remotely connected to it. Depending on the type of connection and the distance of data movement, there is a process of data import, export or data transmission:

- Data import and export process: Perform short-distance data movement between

computers and devices directly connected.

- Data transmission process: Perform long-distance data movement between computers

computers and remote connection devices.

- Control: Inside the computer system, the control unit is responsible for managing computer resources and coordinating the operation of functional components in accordance with requests received from users.

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