Fundamentals of NetworkingDiscovery 1, Chapter 6Network Services

Objectives•Compare and contrast clients and servers, and their

interaction over the network.

•Describe the type of interactions of Internet applications.

•Describe the purpose of a layered model.

• Illustrate the interaction on various protocols.

Introduction•Everyday we communicate across the Internet▫What kinds of activities?

•What’s in common with all of these?▫Servers

•All these interactions use standards & protocols

Client-Server•Web Page Request▫Client has web client

software Browser- widely used

client software▫Server

Host running an application that provides info or services to a client

Types of Servers

Web Site domain names to IP address translation

Remote login to device to control it

Send/Receive email

Assigns IP addresses

Web Site File Transfer

Activity•Complete 6.1.1.4▫Match the service to the client’s request

Standardized Communication•Different computers & operating systems across the

Internet▫Communication not possible if they didn’t share a

protocol

•Phone call China to US▫We have connectivity▫A Chinese sales person couldn’t be understood by an

English speaking person▫That’s why there’s protocols (rules) to follow

Licklider•DoD•Saw the need for

networked computers•3 bidders w/ different

systems▫They couldn’t communicate

with each other▫Came up with the idea of

ARPAnet, which later became the Internet

Client Server Interaction•A web server & client use specific protocols and

standards in exchanging info to ensure that the messages are received & understood.

•Application, transport, Internetwork and network access protocols

Client Server Interaction•Application Protocols•HTTP▫Rules for how browser & web

server interact

•You request web page•Another protocol delivers it

Client Server Interaction•Transport Protocols•TCP▫Manages the conversations/packet exchange▫Splits message into segments▫Flow control & acknowledgments between the hosts▫Retransmission

Client Server Interaction• Internetwork Protocols• IP▫Assigns IP addresses▫Encapsulate into packets for routing

Client Server Interaction•Network Access Protocols▫Get on the Ethernet cable!!!

•Data Link Management▫Takes packets & encaps them into frames▫MAC addresses are attached here

•Physical Transmission▫How bits go on media (wired, wireless)

Overview

Review•Which server…▫Translates names to IP addresses?▫Used for remote login?▫Assigns IP addresses?

•Which protocol…▫Splits data into segments?▫Controls flow of data?▫Acknowledges receipt of data?▫Requests retransmission if a piece is missing?

End of Day One

Review•Which protocol adds the IP addresses?

•Which category of protocols encapsulates packets into frames?

•Which protocol is for the rules of how a browser & web server communicate?

TCP & UDP Transport Protocols• Each protocol does its’ own

job▫ IP addresses & routes data

Doesn’t say how it is transported

• Different applications use different protocols for transport of the data▫ How data is sent/exchanged

• TCP or UDP

Transmission Control Protocol•Used when an application requires an

acknowledgement▫ Like a registered letter in the mail

•Breaks messages into small numbered segments▫ If sender doesn’t get an ACK of message received, it

retransmits ▫Only portion lost is resent

•On receiving host, TCP reassembles data•FTP & HTTP are examples of protocols using TCP• Look at 6.1.3.2 Example

User Datagram Protocol•Used for faster transmissions• “Best effort delivery” ▫Standard postal letter

•No ACK or retransmission•Used for streaming audio or video, Internet radio,

VoIP

UDP & Internet Radio• If some of the message is

lost, it is not retransmitted. ▫ You might hear a slight

break in the sound. • If TCP were used and the

lost packets were resent, the transmission would pause to receive them and the disruption would be more noticeable.

Compare TCP & UDP• Let’s do this together

Review

Keep Track of Conversations•All the conversations need to be tracked▫Port Number▫A # in each segment▫Helps identify what service the message is for

Web request, email, DHCP, etc.

Port Numbers & Communication•Each message sent, has a source & destination port

number•Source Port- randomly generated▫Placed into the segment

Port Numbers, Communication & Sockets

•The combo of the source & destination IP AND the source & destination port number is known as a socket. ▫Used to identify the server and service being requested

by the client. ▫Thousands of requests per day are tracked by this

Destination Port Numbers•Destination- tells about service requested▫80- HTTP▫25- SMTP▫53- DNS▫21- FTP▫23- Telnet

Application Protocols

& Services

Domain Name Service•Server with table of IP &

host names•Request sent to port 53

(DNS)▫DNS server looks in table

to translate it▫ If there, it lets client know▫ If not there, forwards to

another DNS server If no learn, time out

Lab•DNS Lab▫Lab 6.2.1.3 Handout▫Use nslookup

Review•What does www.gcit.org represent?▫An IP address

•Which server would translate that name to an IP address?▫DNS server

•Which server would assign IP addresses?▫DHCP server

•Which Application protocol does FTP use?▫TCP

Review•Why would an application use UDP?▫No disruption if dropped packets (fast)▫Slight interruption, but it keeps going

•Which protocol is used for web sites?▫HTTP

•Which port # is…▫FTP

21▫HTTP

80

Web Communication•You want www.cisco.com•DNS gets you the IP address of it•Your browser uses that IP & port 80 to request the

web page•Socket connection made with server•Web page comes back to your browser encoded in

HTML

Web Clients & Servers•HTTP is not secure•Secure HTTP (https:) is port 443

Lab•Packet Tracer 6.2.2.2 together

FTP Clients & Servers•Transfer files from host to host•Built in to OS & browsers•Also GUI based software available

•Client/Server•Uses TCP•Request to server on port 21•Port 20 to send files to client

FTP•Up/downloading of files, music, web site

Email•Email server receives & stores emails•You email client allows access to view messages•user@company.domain •Protocols used in email include SMTP, POP3, IMAP4

Email Protocols- SMTP•SMTP (25)▫Used to send email from client to server▫Email server to email server

Email Protocols- POP3•POP3 (110)▫Used to send client messages & deleted from storage

on the server Mail on server until collected from client

Email Protocols- IMAP4• IMAP4 (143)▫Like POP3, but it keeps messages on server until user

deleted them

Email Communication & Protocols

Configuring Email Example

Review

IM Protocols: Clients & Servers•Real-time communication•Each IM service may use different protocols &

destination ports▫So you must have compatible IM software

Voice Protocols: Clients & Servers•VoIP•Can call similar clients▫Calls to landlines need public phone network

More About Port Numbers- 6.2.7.2•1-65,535•Well-known ports▫1- 1023▫Common applications

•Registered ports▫1024- 49,151▫Can be source or destination ports▫Used for specific applications like IM

•Private ports▫49,152 & above ▫For source ports

Port # Review•6.2.7.2

Review•Which email service protocol…▫Is used to send mail to server?

SMTP▫Is used to get mail from the server & keep it there until

deleted? IMAP4

▫Is used to communicate from email server to email server? SMTP

▫Is used to get mail from the server & delete it? POP3

Layered Model &

Protocols

Protocol Interaction•They interact with each other▫Protocol Stack

•Some protocols focus on content of message

•Others focus on moving the data

•Protocols visualized in layers

TCP/IP Model

Sending a Message•Web Server to client (you)▫Application data broken into TCP segments

Each segment has a header w/ source & dest ports▫Segment encapsulates HTTP & HTML data▫Encapsulates into a packet w/ IP header

IP header has source & dest IP addresses▫IP Packet sent to Ethernet protocol

Encapsulates into frame header & trailer Source & destination MAC AND error checking

▫Bits encoded onto the media

Sending- 6.3.2.1

Receiving a Message- 6.3.2.2• Last process in reverse▫Bits received by NIC & decoded

Destination MAC recognized▫Ethernet header & trailer removed

Source & dest MAC removed▫IP header removed

Source & dest IP removed▫TCP header removed

Source & dest ports removed▫Web page data passed to HTTP & browser▫TCP segment received, reassembled, & page displays

TCP/IP Model Match

OSI Model•Primary model for

protocol development•Unlike TCP/IP model,

this is for all protocols

Viewing OSI in Packet Tracer

Activity- 6.3.3.3•192.168.5.101

•80 or TCP or UDP

•01-5A-FF-65-80-DC

•1100101101000010

•DHCP or POP3 or HTTP

Activity•Handout 6.3.3.4•Packet Tracer 6.3.3.5

Review 1- 9 Questions

Advanced Review

Fundamentals of NetworkingDiscovery 1, Chapter 6Network Services