1. Computer Networks and Internets Term Presentation ASLIHAN BÜLBÜL 28672442386 2867244238619.11.2007-23.11.2007

2. Client/Server Architecture What are Client and Server? What are Client and Server? Characteristics of Clients and Servers Characteristics of Clients and Servers Information Flow between Client and Servers Information Flow between Client and Servers Communication Paradigm Communication Paradigm The important issues about Client Server Communication The important issues about Client Server Communication Most Commonly Used Server Types Most Commonly Used Server Types Web Server Web Server E-mail Server E-mail Server FTP Server FTP Server IRC Server IRC Server DNS Server DNS Server Telnet/SSH Server Telnet/SSH Server DHCP (Dynamic Host Configuration Protocol) DHCP (Dynamic Host Configuration Protocol)

3. What are Client and Server? What is Client? What is Client? What is Server? What is Server?

4. Characteristics of Client and Servers Client Software Local running. (on PC). Local running. (on PC). Contact initiator. Contact initiator. Active contact with one remote server at a time. Active contact with one remote server at a time. No need of special hardware or sophisticated OS. No need of special hardware or sophisticated OS. For one session execution. For one session execution. Arbitrary application program. Arbitrary application program. Server Software Not local running. Contact expectant. Contact from arbitrary clients, but offering a single service. Need of powerful hardware and sophisticated OS. One service, many clients. Special-purpose program.

5. Information Flow Between Client and Servers Type of Information flow. Type of Information flow. Request-Response Mechanism. Request-Response Mechanism. Server behaviors in Request- Response Mechanism. Server behaviors in Request- Response Mechanism. Client behaviors in Request- Response Mechanism. Client behaviors in Request- Response Mechanism.

6. Communication Paradigm Establish communication. Establish communication. Exchange messages. Exchange messages. Terminate communication. Terminate communication. Ex. Video: Ex. Video: http://www.youtube.com/wat ch?v=ey9HCvTIO70 http://www.youtube.com/wat ch?v=ey9HCvTIO70 http://www.youtube.com/wat ch?v=ey9HCvTIO70 http://www.youtube.com/wat ch?v=ey9HCvTIO70

7. The important issues about Client Server Communication Client and Server communication protocols. Client and Server communication protocols. Working style of Client and Servers. Working style of Client and Servers. How can a client find server? How can a client find server? Port Numbers. Port Numbers. How can server’s hardware capacity and internet connection speed can be specified? How can server’s hardware capacity and internet connection speed can be specified?

8. Most Common Server Types Web Server Publishing web sites. Publishing web sites. Importance of Adjusting connection capacity Importance of Adjusting connection capacity In LANs or ISP’s system rooms(colocation). In LANs or ISP’s system rooms(colocation). Web hosting Web hosting Need of: 7x24 internet connection 7x24 internet connection Real and static IP address Real and static IP address Domain name Domain name Port situation (80th TCP port) Port situation (80th TCP port) Examples: Open Source Apache Server on Linux, IIS(Internet Information System) on Windows XP OS, Windows 2000.

9. Most Common Server Types-2 E-Mail Server: Delivery of e-mail from sender to receiver’s e-mail server. Delivery of e-mail from sender to receiver’s e-mail server. Saving e-mails and deliver them when user connects. Saving e-mails and deliver them when user connects. E-mail sending operation: E-mail sending operation: 1.Connecting to the server. 2.Sending e-mail. 3.Looking receiver address’s domain name by server. (xxx@ddd.com) xxx@ddd.com 4.Delivering the mails according to domain name. (if same domain deliver to own POP3 server, otherwise ask to the DNS server and learn the IP address). 5.Send e-mail with STMP(Simple Mail Transfer Protocol) to the other server. 6.Looking to the user name of this e-mail address and accept this e-mail.

10. Most Common Server Types-3 FTP(File Transfer Protocol) Server: A program or file transfer from network. A program or file transfer from network. Download links Download links Connecting to FTP: Connecting to FTP: Web browsers Command line of OSs. FTP Client Programs (cuteFTP, FlashFXP) Updating web sites. Updating web sites. Remote control of PC. Remote control of PC. User types (anonymous and private) and security. User types (anonymous and private) and security. Ex: for Linux, ProFTP, PureFTP Ex: for Linux, ProFTP, PureFTP for Windows, an FTP Server exists with IIS(Internet Information Server) Uses TCP 21th port. Uses TCP 21th port.

11. Most Common Server Types-4 IRC (Internet Relay Chat) Server: Communication and chat. Communication and chat. Basic client server paradigm. Basic client server paradigm. More than one clients and server at the scene. More than one clients and server at the scene. Ex: for UNIX/shell: ircII Ex: for UNIX/shell: ircII for Windows:mIRC or PIRCH for Macintosh Ircle

12. Most Common Server Types-5 DNS (Domain Name)Server: Conversion between domain names and IPs. Conversion between domain names and IPs. Resource Records (tables). Resource Records (tables). Hierarchical communication of DNS servers. Hierarchical communication of DNS servers. Cache (temporary database) and TTL (time to live). Cache (temporary database) and TTL (time to live). Duties of DNS Duties of DNS Response to Clients Response to Clients Response to other DNS servers. Response to other DNS servers. nslookup command. nslookup command. For client requests UDP 53th port. For client requests UDP 53th port. For other DNS requests TCP 53th port. For other DNS requests TCP 53th port. Mostly used DNS server is BIND (Berkeley Internet Domain). Mostly used DNS server is BIND (Berkeley Internet Domain).

13. Most Common Server Types-6 Telnet/SSH (Secure Shell) Servers: Remote connection and using commands. (LAN and internet) Remote connection and using commands. (LAN and internet) Terminal usage. Terminal usage. E-mail send/receive, e-chat, news group in the past, management and control duties now. E-mail send/receive, e-chat, news group in the past, management and control duties now. Difference of SSH from Telnet. Difference of SSH from Telnet. Text-based servers. Text-based servers.

14. DHCP(Dynamic Host Configuration Protocol) IP address specification. IP address specification. Distributing IP addresses. Distributing IP addresses. IP address pool. IP address pool. Net mask, gateway and DNS server addresses. Net mask, gateway and DNS server addresses.

15. Most Common Server Types Web Server Includes the web sites (hosting). E-Mail Server Includes the e-mail accounts and emails. FTP Server Programs and files for downloading exist here. IRC Server Communication and chat. DNS Server Domain names are converted to IP addresses here. Telnet/SSH Servers Remote connection and using commands.

16. PORTS Definitions and Classification Definitions and Classification TCP (Transport Control Protocol) TCP (Transport Control Protocol) Characteristics of TCP Characteristics of TCP UDP (User Datagram Protocol) UDP (User Datagram Protocol) TCP/UDP and Application Programs TCP/UDP and Application Programs Port Numbers of various application programs Port Numbers of various application programs Packet Loss and Retransmission Packet Loss and Retransmission

17. Definitions and Classification What is PORT? What is PORT? Why port is needed? Why port is needed? Entrance points. Entrance points. Security. Security. Types of ports Types of ports TCP (Transport Control Protocol) TCP (Transport Control Protocol) UDP (User Datagram Protocol) UDP (User Datagram Protocol)

18. TCP (Transport Control Protocol) Segmentation and TCP Segmentation and TCP Secure Communication Secure Communication Advantage and disadvantages of security Advantage and disadvantages of security Source Port Source Port Destination Port Destination Port Connection-Oriented Connection-Oriented SYN, SYN/ACK, ACK, FIN SYN, SYN/ACK, ACK, FIN Acknowledgement information Acknowledgement information Optimum Window Size (536 byte) Optimum Window Size (536 byte) Source Port Destination Port Sequence Number Acknowledgement Number HlenRserved Code bits Window Checksum Urgent Pointer Options (optional) Padding Data ….

19. Characteristics of TCP Connection-Orientation Connection-Orientation Point-To-Point Communication Point-To-Point Communication Complete Reliability Complete Reliability Full Duplex Communication Full Duplex Communication Stream Interface Stream Interface Reliable Connection Startup Reliable Connection Startup Graceful Connection Shutdown Graceful Connection Shutdown

20. UDP (User Datagram Protocol) Simpler than TCP Simpler than TCP No handshaking No handshaking Not secure communication Not secure communication No acknowledgement information No acknowledgement information Advantages and disadvantages Advantages and disadvantages

21. TCP/UDP and Application Programs Differences of TCP and UDP Differences of TCP and UDP Where to use TCP or UDP? Where to use TCP or UDP? Simultaneous usage of TCP & UDP Simultaneous usage of TCP & UDP Ex. MSN messenger, Skype Ex. MSN messenger, Skype See the open ports: See the open ports: http://www.youtube.com/watch ?v=fuZylN8ZV_o http://www.youtube.com/watch ?v=fuZylN8ZV_o http://www.youtube.com/watch ?v=fuZylN8ZV_o http://www.youtube.com/watch ?v=fuZylN8ZV_o DNS 53 (UDP) TFTP 69 (UDP) SNMP 161 (UDP) FTP 20 &21 (TCP) Telnet 23 (TCP) SMTP 25 (TCP) HTTP 80 (TCP) POP3 110 (TCP) Port Numbers of some network Servers

22. Packet Loss and Retransmission Acknowledgement message (ACK) Acknowledgement message (ACK) Timer Timer Delay Delay Retransmission Retransmission Concurrent working of application programs. Concurrent working of application programs. Duplicate packets problem Duplicate packets problem

23. IP (Internet Protocols) General Expression about IP General Expression about IP The explanation of IPv4 The explanation of IPv4 IPv4 address format IPv4 address format The explanation of IPv6 The explanation of IPv6 IPv6 address format IPv6 address format Transition Duration to IPv6 Transition Duration to IPv6 IPV4 vs. IPv6 IPV4 vs. IPv6

24. General Expression about IP What is IP? What is IP? The Success of IP: Unique Unique Locator Locator Identifier Identifier Handling heterogeneity Handling heterogeneity IP datagram IP datagram Compatibility Compatibility Frame sizes and IP Frame sizes and IP

25. IPv4 IP and IPv4 IP and IPv4 32 bit address 32 bit address Solving need of IP Solving need of IP NAT (Network Address Translation), CIDR (Classless Inter-Domain Routing), DHCP NAT (Network Address Translation), CIDR (Classless Inter-Domain Routing), DHCP What will happen in 2010s? What will happen in 2010s? Deficiencies of IPv4 Quality of service Quality of service Security Security Compatibility with electronic devices Compatibility with electronic devices IPv4 Routing Protocols IPv4 Routing Protocols

26. IPv4 Address Format Four numbers, each ranging from 0 to 255 Four numbers, each ranging from 0 to 255 Ex. 147.132.42.18 Classes of networks Classes of networks A class (1-126) A class (1-126) B class (128-191) B class (128-191) C class (192-223) C class (192-223)

27. IPv6 Why IPv6 is needed? Why IPv6 is needed? Transition from IPv4 to IPv6 Transition from IPv4 to IPv6 Changes in this transition duration Changes in this transition duration Producers and IPv6 (MAC OS, Solaris, Linux, WinXP/2003) Producers and IPv6 (MAC OS, Solaris, Linux, WinXP/2003) Providing IPv6 support to application programs Providing IPv6 support to application programs IOS (Interface Operating Systems) Nokia, Cisco,3Com IOS (Interface Operating Systems) Nokia, Cisco,3Com Ex. video: http://www.youtube.com/watch?v=qsWNWm2O0_Q Ex. video: http://www.youtube.com/watch?v=qsWNWm2O0_Qhttp://www.youtube.com/watch?v=qsWNWm2O0_Q

28. IPv6 Address Format 8 Pieces, 32 x hexadecimal numbers 8 Pieces, 32 x hexadecimal numbers 32*4=128 bits. Ex: 3FFE:0B00:0000:0000:0000:0000:0000:0046 0000:0000:0000:0000:0000:0000:0000:0 000 0000:0000:0000:0000:0000:0000:0000:0 000 Same with  0:0:0:0:0:0:0:0 or :: 2010:0234:0000:0000:0067:0000:0000:0 0E2 2010:0234:0000:0000:0067:0000:0000:0 0E2 Same with  2010:234:0:0:67:E2 40A1:0000:16FE:0000:0000:0C23:86E1 40A1:0000:16FE:0000:0000:0C23:86E1 Same with  40A1:0:16FE:0:0:C23:86E1 Or 40A1:0:16FE::C23:86E1 40A1:0:16FE::C23:86E1 Only once usage of ::

29. Transition Duration to IPv6 Changes in Client-Server Software Changes in Client-Server Software Cost of change Cost of change Updating; Updating; Client programs, Client programs, OSs, OSs, Hardware Hardware Network Connection device software updates. Network Connection device software updates.

30. IPv4 vs. IPv6 IPv4IPV6 32 bit address 128 bit address Uses base 10 Uses base 16 No abbreviation Allow abbreviation 4 x 8 bits 8 x 16 bits Pieces are separated with “.” Pieces are separated with “:” 127.0.0.1 is loopback address 0:0:0:0:0:0:0:1 or ::1 is loopback address Ex. video: http://www.youtube.com/watch?v=-ZW8v0zd6C0http://www.youtube.com/watch?v=-ZW8v0zd6C0

31. Sources BOOKS: Bilgisayar Ağları ve Güvenliği – Alper ÖZBİLEN (Pusula Yayıncılık) Bilgisayar Ağları ve Güvenliği – Alper ÖZBİLEN (Pusula Yayıncılık) IPv6 clearly explained- Pete LOSHIN IPv6 clearly explained- Pete LOSHIN Internetworking with TCP/IP vol:III Client Server Programming and Applications Internetworking with TCP/IP vol:III Client Server Programming and Applications INTERNET Sources: http://en.wikipedia.org/wiki/IP_address http://en.wikipedia.org/wiki/IP_address http://en.wikipedia.org/wiki/IP_address www.youtube.com (videos) www.youtube.com (videos) www.youtube.com

32. Thank you for listening. Questions