Fundamentals of Networking

1. Fundamentals of Networking Discovery 1, Chapter 6 Network Services

2. 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.

3. 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

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. Client Server Interaction • Application Protocols • HTTP • Rules for how browser & web server interact • You request web page • Another protocol delivers it

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

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

13. 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)

14. Overview

15. 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?

16. 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?

17. 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

18. 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

19. 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

20. 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.

21. Compare TCP & UDP • Let’s do this together

22. Review

23. 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.

24. Port Numbers & Communication • Each message sent, has a source & destination port number • Source Port- randomly generated • Placed into the segment

25. 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

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

27. Application Protocols & Services

28. 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

29. Lab • DNS Lab • Lab 6.2.1.3 Handout • Use nslookup

30. 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

31. 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

32. 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

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

34. Lab • Packet Tracer 6.2.2.2 together

35. 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

36. Up/downloading of files, music, web site FTP

37. 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

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

39. Email Protocols- POP3 • POP3 (110) • Used to send client messages & deleted from storage on the server • Mail on server until collected from client

40. Email Protocols- IMAP4 • IMAP4 (143) • Like POP3, but it keeps messages on server until user deleted them

41. Email Communication & Protocols

42. Configuring Email Example

43. Review

44. IM Protocols: Clients & Servers • Real-time communication • Each IM service may use different protocols & destination ports • So you must have compatible IM software

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

46. 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

47. Port # Review • 6.2.7.2

48. 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

49. Layered Model & Protocols

50. 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