chapter 2 communicating over the network cis 81 networking fundamentals rick graziani cabrillo...

Chapter 2Communicating Over the Network

CIS 81 Networking Fundamentals

Rick Graziani

Cabrillo College

[email protected]

Last Updated: 2/17/2008

2

This Presentation

For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please email me for a username and password. Email: [email protected] Web Site: www.cabrillo.edu/~rgraziani

The Platform for Communications

4

Elements of Communication

5

Communicating the Messages

Theoretically, single communication, such as a music video or an e-mail message, could be sent across a network from a source to a destination as one massive continuous stream of bits.

No other device would be able to send or receive messages on the same network.

Results in significant delays. Inefficient use of channel or link. Any loss in data, entire message would have to be resent.

00101010100101010101010101010101010

I have to wait…

Continuous stream of bits

6


Better approach – segmentation. Division of the data stream into smaller pieces is called segmentation.

Segmentation has two benefits…

Segmentation

7


Benefits of segmentation: Multiplexing:

Different conversations can be interleaved on the network.

Segmentation

8


Reliability Increase the reliability of network communications. Separate pieces of each message can travel across different paths to

destination. Path fails or congested, alternate path can be used. Part of the message fails to make it to the destination, only the missing

parts need to be retransmitted.

X

9

Disadvantage of Segmentation

Disadvantage – added level of complexity. Like sending a 100 page letter one page at a time.

All of the separate envelopes needed Need to label the pages with a sequence number.

This extra overhead is handled by protocols used to format and address these messages (later).

10

Components of the Network

Devices (hardware) End devices, switch, router, firewall, hub

Media (wired, wireless) Cables, wireless mediums

Services (software) Network applications, routing protocols, processes, algorithms

11

End devices

End devices: Computers (work stations, laptops, file servers, web servers) Network printers VoIP phones Security cameras Mobile handheld devices (such as wireless barcode scanners, PDAs)

End devices are referred to as hosts. A host device is either the source or destination of a message.

12

Each host on a network is identified by an address. IP (Internet Protocol) address (later)

Source Address: 209.67.102.55

Destination Address: 107.16.4.21

209.67.102.55 107.16.4.21

13

Servers and Clients

A host can act as a client, a server, or both. Software installed on the host determines the role.

Servers are hosts that have software installed that enables them to provide information and services, like e-mail or web pages, to other hosts on the network.

Clients are hosts that have software installed that enables them to request and display the information obtained from the server.

Server

Client

14

Intermediary Devices

Intermediary devices: Provide connectivity to the network (switches/hubs) Connect individual networks (routers) Connect segments (links) within the same network (switches/hubs)

Examples: Network Access Devices (Hubs, switches, and wireless access points) Internetworking Devices (routers) Communication Servers and Modems Security Devices (firewalls)

routers

switch or hub

switch or hub

15

Network Media

Network media: The medium provides the channel over which the message travels from source to destination. Metallic wires - encoding into patterns of electrical impulses. Fiber optics – encoding into pulses of light (infrared or visible light ranges) Wireless – encoding patterns of electromagnetic waves.

(Later: OSI Physical Layer)

16

Network Media

Different media considerations: Distance it can carry the signal Environment it works in Bandwidth Cost of medium and installation Cost of connectors and equipment

17

Local Area Network (LAN)

Local Area Network (LAN) An individual network usually spans a single geographical area, providing

services and applications to people within a common organizational structure, such as a single business, campus or region.

LAN devices Switches (and hubs) Routers Multilayer switches

18

Wide Area Network (WAN)

Wide Area Networks (WANs) Leased connections through a telecommunications service provider

network. Networks that connect LANs in geographically separated locations

Telecommunications service provider (TSP) interconnect the LANs at the different locations.

TSPs transported voice and data communications on separate networks. Providers are now offering converged information network services to their

subscribers.

T1, DS3, OC3 PPP, HDLC Frame Relay, ATM ISDN, POTS

19

The Internet – A Network of Networks

ISPs (Internet Service Providers) are often also TSPs. Connect their customers to the Internet. The Internet is created by the interconnection of networks belonging to ISPs. ISPs cooperate with other ISPs and TSPs to make sure their customers have

access to all Internet networks. BGP peering and routing is used.

20

CENIC – ISP for K-12, Community Colleges, CSU and UC

ISPs route traffic within their own group of networks (autonomous system). ISPs connect their networks to other ISPs networks. Within the ISP’s networks are both WANs and customer LANs

21

Network Representations

Network Interface Card (NIC) - Provides the physical connection to the network at the PC or other host device.

Physical Port - A connector or outlet on a networking device where the media is connected to a host or other networking device.

Interface - Specialized ports on an internetworking device that connect to individual networks. Because routers are used to interconnect networks, the ports on a router

are referred to network interfaces.

Protocols

23

Protocol

Protocol – Rules that govern communications. Protocol suite - A group of inter-related protocols that are necessary to

perform a communication function.

24

Multiple protocols (encapsulated)

The message received by the host usually contains multiple protocols, plus the actual data.

Note: Application Header (HTTP) may or may not exist. Typically Application Header or Data. (later)

HTTP Header Data

Frame Header IP Header TCP HeaderApp Header Frame Trailer

Data

Protocols

25

Multiple protocols (encapsulated)

Encapsulation – Process of adding a header to the data or any previous set of headers.

Decapsulation – Process of removing a header. More later.

HTTP Header Data

Frame Header IP Header TCP HeaderApp Header Frame Trailer

Data

Protocols

26

Example: Protocol – IPv4

Example of IPv4 More later

Frame Header IP Header TCP Header Frame Trailer

Data

HTTP Header

27

209.67.102.55 107.16.4.21

Frame Header IP Header TCP Header Frame Trailer

Data

209.67.102.55107.16.4.21

HTTP Header

28

Protocols

Networking protocols suites describe processes such as: The format or structure of the message The process by which networking devices share information about

pathways with other networks How and when error and system messages are passed between devices The setup and termination of data transfer sessions

29

Early days – proprietary network equipment and protocols. Now – Industry standards Institute of Electrical and Electronics Engineers (IEEE)

Develops standards in telecommunications, information technology and power generation.

Examples: 802.3 (Ethernet), 802.11 (WLAN) Internet Engineering Task Force (IETF)

Internet standards RFCs (Request for Comments) Example: TCP, IP, HTTP, FTP

Protocol Suites and Standards

30

Interaction of Protocols

Hypertext Transfer Protocol (HTTP) Common protocol that governs interaction between web server and a web

client. Defines the content and formatting of the requests and responses between the

client and server. Both the client and the web server software implement the HTTP application. HTTP relies on other protocols to govern how the messages are transported

between client and server.

31


Transmission Control Protocol (TCP) Transport protocol that manages the individual conversations between servers

and clients (not just web servers and web clients) TCP divides the HTTP messages into smaller pieces, called segments Responsible for controlling the information exchanged between the server and

the client: Size of data Flow control – how much is sent and received Reliability – Sequence numbers in case lost or missing

segment

32

Internetwork Protocol (IP) Responsible for taking the formatted segments from TCP, encapsulating them

into packets. Assigns the appropriate source and destination addresses,

Original source address of host Final destination address of host Used by routers in selecting the best path to the destination host.

packet

33


Network access protocols (Data link and Physical layer protocols) Physical transmission of data on the media. Take the packets from IP and format them to be transmitted over the media.

frame

34


Network access protocols (Data link and Physical layer protocols) Responsible for addressing and sending the IP packet between two devices on

the same network. Host to router Router to router Router to host

209.67.102.55 107.16.4.21

35

Technology-Independent Protocols

Protocols are not dependent upon any specific technology. For example:

Our IP Packet (IP + TCP + HTTP + Data) can be delivered over various types of networks using a variety of data link frames.

More later! – Herding cats.

Frame Header IP Header TCP Header Frame TrailerHTTP Header

T1, DS3, OC3 PPP, HDLC Frame Relay, ATM ISDN, POTS

Ethernet Ethernet

IP PacketIP Packet

Using Layered Protocols

37

Layered Model

Layered Models separate the functions of specific protocols.

38

Using a layered model: Have defined information that they act upon and a defined interface to the

layers above and below. Fosters competition because products from different vendors can work

together. Prevents technology or capability changes in one layer from affecting other

layers above and below. Provides a common language to describe networking functions and

capabilities.

Benefits of a Layered Model

39

Protocol and Reference Models

A protocol model provides a model that closely matches the structure of a particular protocol suite.

A reference model provides a common reference for maintaining consistency within all types of network protocols and services. Not intended to be an implementation specification.

40

Protocol and Reference Models

The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. OSI is also a protocol suite or protocol model. OSI lost out to TCP/IP as the protocol suite of the Internet. OSI protocol suite includes layers 3 through 7

41

TCP/IP Model

TCP/IP Model and Protocol Suite is an open standard. No one company controls it.

Governed by IETF Working Groups with standards proposed using Request for Comments (RFCs).

42

Example: RFC 791 IPv4

43

The Communication Process - Encapsulation

Server

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

HTTP Data

Encapsulation – Process of adding control information as it passes down through the layered model.

Note: Application Header (HTTP) may or may not exist. (later)

44

The Communication Process - Decapsulation

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

Client

HTTP Data

Decapsulation – Process of removing control information as it passes upwards through the layered model.

45

Wireshark will let us examine protocols!

46

The Communication Process

Protocol Data Unit (PDU) - The form that a piece of data takes at any layer. At each stage of the process, a PDU has a different name to reflect its new

appearance. PDUs are named according to the protocols of the TCP/IP suite.

Data - The general term for the PDU used at the Application layer Segment - Transport Layer PDU Packet - Internetwork Layer PDU Frame - Network Access Layer PDU Bits - A PDU used when physically transmitting data over the medium

47

ISO and the OSI Model

The International Organization for Standardization (ISO) released the OSI reference model in 1984, was the descriptive scheme they created.

“ISO. A network of national standards institutes from 140 countries working in partnership with international organizations, governments, industry, business and consumer representatives. A bridge between public and private sectors.” www.iso.ch

http://www.iso.ch/

48

OSI Model

It breaks network communication into smaller, more manageable parts.

It standardizes network components to allow multiple vendor development and support.

It allows different types of network hardware and software to communicate with each other.

It prevents changes in one layer from affecting other layers.

It divides network communication into smaller parts to make learning it easier to understand.

49

OSI Model

Presentation and Session layers are not commonly referred to in most instances.

50

Comparing OSI and TCP/IP Models

Network Addressing

52

Layer 3 addresses are primarily designed to move data from one local network to another local network within an internetwork.

Layer 2 addresses are only used to communicate between devices on a single local network,

53

Layer 2 Addresses (Data Link Layer) Includes the host physical address. Layer 2 is concerned with the delivery of messages on a single local network. The Layer 2 address is unique on the local network and represents the address

of the end device on the physical media. In a LAN using Ethernet, this address is called the Media Access Control (MAC)

address. When two end devices communicate on the local Ethernet network, the frames

that are exchanged between them contain the destination and source MAC addresses. (later)

54

Ethernet LAN - Multiaccess

On an Ethernet LAN there are usually more than just two devices.

There can be hundreds, even thousands of devices on a single LAN.

Need a way to send it to a specific device on the LAN.


Destination Address

Source Address InternetWho are you?

55

Ethernet LAN - Multiaccess

Ethernet LANs are multiaccess networks. Multiple devices can access the network

(even at the same time). Ethernet NICs have unique 48 bit MAC

addresses. (much more later)


Destination Address

Source Addressaaa

bbb

ccc

ddd

eee

111

222

333

444

555

666

777

888

999

000

123

These Ethernet addresses are abbreviated for brevity.

Internet

987

56

Layer 2 addresses, including Ethernet MAC addresses are used to get the IP packet from one device to another device on the same network.


Destination Address: 888

Source Address: aaaaaa

bbb

ccc

ddd

eee

111

222

333

444

555

666

777

888

999

000

123


Internet

987

Sending an IP Packet to a device within the LAN

57

The Layer 2 destination address is always a layer 2 address within that network.

Disregarding using proxies which are uncommon.


Destination Address: 987

Source Address: aaaaaa

bbb

ccc

ddd

eee

111

222

333

444

555

666

777

888

999

000

123


Internet

987

Sending an IP packet outside the LAN

58

What is the Address on my Ethernet NIC?

59

Serial vs Multiaccess NetworkSerial (PPP)

Multiaccess (Ethernet)

60

Serial point-to-point networks

PPP – Point-to-Point Protocol (later) Only two devices on this network. No need for unique layer 2 address. Can use anything. PPP uses an 8 bit broadcast address – FF - Hex (all 1’s binary)

61

IP: 192.168.4.10

IP: 172.16.35.5

MAC: DD-DD-DD-44-44-44

MAC: AA-AA-AA-11-11-11

PPP

MAC: CC-CC-CC-33-33-33

MAC: BB-BB-BB-22-22-22

PPP

PPP

What are the frame and packet addresses at every point from Host A to Host D?

A

D


L2 Destination Address?

L3 Source Address?L3 Destination Address?

L2 Source Address?

W X

YZ

62

Layer 3 Addresses (Network Layer) Layer 3 addresses are primarily designed to move data from one local network to

another local network within an internetwork. At the boundary of each LAN a router, decapsulates the frame to read the

destination host address contained in the header of the packet. Routers use the Layer 3 destination address to determine which path to use to

reach the destination host. Once the path is determined, the router encapsulates the packet in a new frame

and sends it on its way toward the destination end device. When the frame reaches its final destination, the frame and packet headers are

removed and the data moved up to Layer 4.

63

The sending host builds message with multiple encapsulations.

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

Dest. MAC 0B-31

Source MAC 00-20

Type 800

TrailerDest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

DataDest. Add FF-FF

Source Add Type 800

TrailerDest. MAC 0B-20

Source MAC 0C-22

Type 800

Trailer

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

DataHTTP Header

TCP Header

IP Header

Data Link Header

Data Link Trailer

The receiving host receives the message with multiple decapsulations.

64

Getting Data to the Right Application

Layer 4 (TCP/UDP) contains a port number which represents the application or service carried in the IP packet. Destination port – destination application Source port – source application

More later.

65

Getting Data to the Right Application

Destination port number tells the OS (TCP/IP) stack which application to hand the data to.

Examples: 80 = HTTP (www) 23 = Telnet 20, 21 = FTP 25 = SMTP

Chapter 2Communicating Over the Network

CIS 81 Networking Fundamentals

Rick Graziani

Cabrillo College

[email protected]

Last Updated: 2/17/2008

chapter 2 communicating over the network cis 81 networking fundamentals rick graziani cabrillo...

Documents

destination address

network switcheshubsexamples

network access devices

email message

entire message

host device

pdas end devices

wireless resources