CS计算机代考程序代写 PowerPoint Presentation

PowerPoint Presentation

Deakin University CRICOS Provider Code: 00113B

SIT182 – Real World Practices For Cyber Security

Trimester 2 – 2021
Deakin College

Week 4 – Part 1

Deakin University CRICOS Provider Code: 00113B

• Basic Networking Background

2

Topics,

Deakin University CRICOS Provider Code: 00113B

NOTE

• This unit is not aiming to teach you ALL about networking. You will have other units for this in your
degree.

• Concepts covered here are just the very minimum knowledge that you need to have so we can
cover some of the basics of network security.

Deakin University CRICOS Provider Code: 00113B

Protocol

• A Protocol is an agreement on how to communicate

• Specifies the syntax
• Format of messages
• Order in which they’re exchanged

• Specifies the semantics
• What messages mean
• What to do on message send or receive, or at specified times

• Defines a language for communications

Deakin University CRICOS Provider Code: 00113B

Internet Protocol (IP)

• The Internet Protocol (IP) is what lets computers communicate around the
world.

• Has a well-defined binary representation for transmission over the
networks it comprises.

• Everything is big-endian (aka Network byte order)

• Any IP-enabled host receiving an IP packet knows how to handle it,
because of the protocol.

Deakin University CRICOS Provider Code: 00113B

End-to-End Principles

A and B are End hosts

• on the periphery of the network

• not physically connected

• communicate through the network

Ri are Routers

• in the interior of the network

• Routing specifies how to get from A to B

• Forwarding moves traffic towards B

End-to-end Principles: knowledge/control of connections exclusively at
the periphery

Interior nodes only forward packets based on local delivery rules

Deakin University CRICOS Provider Code: 00113B

An Analogy

Postal service:
You write a letter to your friend
You seal that letter in an envelope
You write your friend’s address on the envelope
You drop that envelope in themail
Australia Post picks it up

Internet:
You click on a link in your webbrowser
Your browser constructs a packet with the GET request
Your browser adds the server’s address to the packet
Your computer sends that packet out its network interface
The gateway router receives that packet

Deakin University CRICOS Provider Code: 00113B

An Analogy

Postal service: Envelope → Destination with successively smaller hops

State -> City -> Street -> Address -> Apartment number

⇒ Australia Post never knows contents of envelope

Internet: Packet → Destination with successively smaller hops

ISP (Internet Service Provider) -> Region -> Organization’s network -> Office’s
subnet -> Server
⇒ Routers never look at payload of packet

Layers

• Abstract network protocol into separate layers

• Each layer controls some aspect of

communications

• A layer relies on services provided by the layer

below it

• A layer provides services to the layer above it

(Similar to how software is designed)

• Each layer has a distinct role

The Network Stack

• Open Systems Interconnection (OSI) Model

• Defines 7-Layer Model for the network stack

• We will only worry about 5 of these -☺

• As with software stack, each layer has a distinct

role

• These roles are codified/implemented with

protocols

How Protocol Stack Works

Physical Layer

How to encode bits for a single physical link

►Voltage levels

►RF modulation

►Photon wavelengths/intensities

Lots of technologies

►Coaxial cable

►Twisted-pair cable

►RF broadcast

►Fiber-optic cable

Link Layer

• Combines bits into frames
• Provides local addressing (MAC—Media Access

Control)
• Supports point-to-point and often broadcast

delivery

MAC address of a device
shown in MS Windows OS

Link Layer

• Link-layer connections grouped into subnets

• Link-layer protocol used to transmit messages within this subnet. MAC addresses must be unique.

⇒ Device can join any subnet
⇒ Address space partitioned by manufacturers (MAC is fixed and unique, which is included by the
device manufacturer)

What is a subnet?

• A subnet is a logical partition of an IP
network into multiple, smaller
network segments.

• The internet is composed of many
networks that are run by many
organizations. In turn, each
organization’s network can be
composed of many smaller networks,
or subnets. Each subnet allows its
connected devices to communicate
with each other, and routers are used
to communicate between subnets.

Network Layer

• Bridges subnets for end-to-end connectivity

• Provides global addressing (IP addresses — 32 bits)

• Delivery is best-effort

⇒ No retransmissions
⇒ No message integrity

• Data is encapsulated in packets

⇒ payload for Link-layer (Layer 2) frames

Internet: network of networks using the Internet Protocol

https://thumbs.dreamstime.com/z/tcp-ip-network-model-28867280.jpg

Network Layer

• IP addresses are locally unique
⇒ assigned within a subnet (CIDR notation: 192.168.0.0/16)
⇒ some hosts not globally addressable

• A router is a device that implements up through Network layer (Layer 3)

⇒ connects multiple subnets

⇒ different IP addresses on each interface

Deakin University CRICOS Provider Code: 00113B

IP Networks – Simply Put

• Data is divided into packets
• Internet delivers packets between IP addresses

Deakin University CRICOS Provider Code: 00113B

Routers – Simply Put

• Each router forwards packets to the next based on the destination address
• Unreliable (best effort), routers may drop packets
• Not through predefined route – different factors such as load affect the route a packet

takes

Packet Switching: example

A

C

B

D

F

E

3 2 1Packets

A

C

B

D

F

E

3 2

1

Packets

Packet Switching: example

A

C

B

D

F

E

3

21

Packets

Packet Switching: example

A

C

B

D

F

E

321

Packet Switching: example

Computer Networks

24

Transport Layer

End-to-end communication between processes

UDP (User Datagram Protocol)

► UDP socket contains the port number and

IP address of the destination only

► unreliable, best effort, no packet retransmission

if it gets lost

► datagram-based (single-packet messages)

TCP (Transmission Control Protocol)

► TCP socket contains the port numbers and IP addresses of the source & destination

► reliable, keeps track of data sent/received

► retransmission of lost packets

► byte-based (messages/sessions span possibly many packets)

Computer Networks

25

Application Layer

What users/processes interact with

Choice of transport depends on what is needed

► Web browsing ⇒ TCP

► Email ⇒ TCP

► Voice calls ⇒ UDP

Defines its own data formats and protocols, within TCP or UDP

► Web browsing ⇒ HTTP (Hypertext Transfer Protocol)

► Email ⇒ SMTP (Simple Mail Transfer Protocol)

► Voice calls ⇒ RTP (Real-time Transport Protocol)

Computer Networks

26

Endpoint Names

Each protocol layer has its own way of naming endpoints:

• Ethernet (MAC) addresses in the link layer (e.g. 00-B0-D0-05-04-7E)

• IP address in the network layer (e.g. 157.58.56.101)

• TCP port number + IP address

• URL in web services (e.g. http://www.tempurl.org/myservice)

Computer Networks

27

Network Protocols in 1-slide

Deakin University CRICOS Provider Code: 00113B

References and Further Reading

What’s a Network: https://www3.nd.edu/~cpoellab/teaching/cse40814_fall14/networks.pdf
[Chapter: An Introduction to Information Networks] Introduction to Computer Networks and Cybersecurity, J.
Irwin, CRC Press.

https://www3.nd.edu/~cpoellab/teaching/cse40814_fall14/networks.pdf

Deakin University CRICOS Provider Code: 00113B

Acknowledgement

Acknowledging the kind support and contribution of:
Dr Arash Shaghaghi (Deakin University, Australia), Prof. Chang-Tsun Li (Deakin University, Australia), Prof. Sanjay
Jha (The University of New South Wales, Australia), Dr. Nicolas Courtois (University College London, UK), Dr George
Danezis (University College London, UK), and Dr Michael March (University of Maryland, USA).