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•[email protected] •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