Computer Computer Networks and Networks and

Internets Internets Term Term

PresentationPresentationASLIHAN BÜLBÜLASLIHAN BÜLBÜL

286724423862867244238619.11.2007-23.11.200719.11.2007-23.11.2007

Client/Server ArchitectureClient/Server Architecture

What are Client and Server?What are Client and Server? Characteristics of Clients and ServersCharacteristics of Clients and Servers Information Flow between Client and ServersInformation Flow between Client and Servers Communication ParadigmCommunication Paradigm The important issues about Client Server CommunicationThe important issues about Client Server Communication Most Commonly Used Server TypesMost Commonly Used Server Types

Web ServerWeb Server E-mail ServerE-mail Server FTP ServerFTP Server IRC ServerIRC Server DNS ServerDNS Server Telnet/SSH ServerTelnet/SSH Server DHCP (Dynamic Host Configuration Protocol)DHCP (Dynamic Host Configuration Protocol)

What are Client and Server?What are Client and Server?

What is Client?What is Client?

What is Server?What is Server?

Characteristics of Client and ServersCharacteristics of Client and Servers

Client SoftwareClient Software Local running.Local running. (on PC).(on PC). Contact initiator.Contact initiator. Active contact with one remote Active contact with one remote

server at a time.server at a time. No need of special hardware No need of special hardware

or sophisticated OS.or sophisticated OS. For one session execution.For one session execution. Arbitrary application program.Arbitrary application program.

Server SoftwareServer Software Not local running.Not local running. Contact expectant.Contact expectant. Contact from arbitrary clients, Contact from arbitrary clients,

but offering a single service.but offering a single service. Need of powerful hardware Need of powerful hardware

and sophisticated OS.and sophisticated OS. One service, many clients.One service, many clients. Special-purpose program.Special-purpose program.

Information Flow Between Client and Information Flow Between Client and ServersServers

Type of Information flow.Type of Information flow. Request-Response Request-Response

Mechanism.Mechanism. Server behaviors in Request- Server behaviors in Request-

Response Mechanism.Response Mechanism. Client behaviors in Request- Client behaviors in Request-

Response Mechanism. Response Mechanism.

Communication ParadigmCommunication Paradigm

Establish communication.Establish communication. Exchange messages.Exchange messages. Terminate communication.Terminate communication. Ex. Video:Ex. Video: http://http://

www.youtube.com/watch?vwww.youtube.com/watch?v=ey9HCvTIO70=ey9HCvTIO70

The important issues about Client The important issues about Client Server CommunicationServer 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 How can server’s server’s hardware capacity and internet connection hardware capacity and internet connection speed can be specified?speed can be specified?

Most Common Server TypesMost Common Server Types

Web ServerWeb Server

Publishing web sites.Publishing web sites. Importance of Adjusting connection capacityImportance of Adjusting connection capacity In LANs or ISP’s system rooms(colocation).In LANs or ISP’s system rooms(colocation). Web hostingWeb hosting

Need of: Need of: 7x24 internet connection7x24 internet connection Real and static IP addressReal and static IP address Domain nameDomain name Port situation (80th TCP port)Port situation (80th TCP port)

Examples: Open Source Apache Server on Linux, IIS(Internet Information Examples: Open Source Apache Server on Linux, IIS(Internet Information System) on Windows XP OS, Windows 2000.System) on Windows XP OS, Windows 2000.

Most Common Server Types-2Most Common Server Types-2

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

e-mail.e-mail.

Most Common Server TypesMost Common Server Types-3-3

FTP(File Transfer Protocol) Server:FTP(File Transfer Protocol) Server:

A program or file transfer from network.A program or file transfer from network. Download linksDownload links Connecting to FTP:Connecting to FTP:

Web browsersWeb browsersCommand line of OSs.Command line of OSs.FTP Client Programs (cuteFTP, FlashFXP)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, PureFTPEx: for Linux, ProFTP, PureFTP

for Windows, an FTP Server exists with IIS(Internet Information for Windows, an FTP Server exists with IIS(Internet Information Server)Server)

Uses TCP 21th port.Uses TCP 21th port.

Most Common Server Types-4Most Common Server Types-4

IRC (Internet Relay Chat) Server: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 More than one clients and server at the

scene.scene. Ex: for UNIX/shell: ircIIEx: for UNIX/shell: ircII

for Windows:mIRC or PIRCHfor Windows:mIRC or PIRCH

for Macintosh Irclefor Macintosh Ircle

Most Common Server Types-5Most Common Server Types-5

DNS (Domain Name)Server: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 Cache ((temporary database) and TTL (time to live). temporary database) and TTL (time to live). Duties of DNSDuties of DNS

Response to ClientsResponse 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).

Most Common Server Types-6Most Common Server Types-6

Telnet/SSH (Secure Shell) Servers:Telnet/SSH (Secure Shell) Servers:

Remote connection and using commands. Remote connection and using commands. ((LAN and internet)LAN and internet) Terminal usage.Terminal usage. E-mail send/receive, e-chat, news group in the past, management E-mail send/receive, e-chat, news group in the past, management

and control duties now.and control duties now. Difference of SSH from Telnet.Difference of SSH from Telnet. Text-based servers.Text-based servers.

DHCP(Dynamic Host Configuration DHCP(Dynamic Host Configuration Protocol)Protocol)

IP address specification.IP address specification. Distributing IP addresses.Distributing IP addresses. IP address pool.IP address pool. Net mask, gateway and DNS Net mask, gateway and DNS

server addresses.server addresses.

Most Common Server TypesMost Common Server TypesWeb ServerWeb Server Includes the web sites Includes the web sites ((hosting).hosting).

E-Mail ServerE-Mail Server Includes the e-mail accounts and Includes the e-mail accounts and emails.emails.

FTP ServerFTP Server Programs and files for Programs and files for downloading exist here.downloading exist here.

IRC ServerIRC Server Communication and chat.Communication and chat.

DNS ServerDNS Server Domain names are converted to IP Domain names are converted to IP addresses here.addresses here.

Telnet/SSH ServersTelnet/SSH Servers Remote connection and using Remote connection and using commands.commands.

PORTSPORTS

Definitions and ClassificationDefinitions and Classification TCP (Transport Control Protocol)TCP (Transport Control Protocol) Characteristics of TCPCharacteristics of TCP UDP (User Datagram Protocol)UDP (User Datagram Protocol) TCP/UDP and Application ProgramsTCP/UDP and Application Programs Port Numbers of various application programsPort Numbers of various application programs Packet Loss and RetransmissionPacket Loss and Retransmission

Definitions and ClassificationDefinitions and Classification

What is PORT?What is PORT? Why port is needed?Why port is needed? Entrance points.Entrance points. Security.Security. Types of portsTypes of ports

TCP (Transport Control Protocol)TCP (Transport Control Protocol) UDP (User Datagram Protocol)UDP (User Datagram Protocol)

TCP (Transport Control Protocol)TCP (Transport Control Protocol)

Segmentation and TCPSegmentation and TCP Secure CommunicationSecure Communication Advantage and disadvantages of Advantage and disadvantages of

securitysecurity Source Port Source Port Destination Port Destination Port Connection-OrientedConnection-Oriented SYN, SYN/ACK, ACK, FINSYN, SYN/ACK, ACK, FIN Acknowledgement informationAcknowledgement information Optimum Window Size (536 byte)Optimum Window Size (536 byte)

Source Port Destination PortSource Port Destination Port

Sequence NumberSequence Number

Acknowledgement NumberAcknowledgement Number

HlenHlen RservedRserved Code bitsCode bits WindowWindow

Checksum Urgent PointerChecksum Urgent Pointer

Options (optional) PaddingOptions (optional) Padding

DataData

……..

Characteristics of TCPCharacteristics of TCP

Connection-OrientationConnection-Orientation Point-To-Point CommunicationPoint-To-Point Communication Complete ReliabilityComplete Reliability Full Duplex CommunicationFull Duplex Communication Stream InterfaceStream Interface Reliable Connection StartupReliable Connection Startup Graceful Connection ShutdownGraceful Connection Shutdown

UDP (User Datagram Protocol)UDP (User Datagram Protocol)

Simpler than TCPSimpler than TCP No handshaking No handshaking Not secure communicationNot secure communication No acknowledgement informationNo acknowledgement information Advantages and disadvantagesAdvantages and disadvantages

TCP/UDP and Application ProgramsTCP/UDP and Application Programs

Differences of TCP and UDPDifferences of TCP and UDP Where to use TCP or UDP?Where to use TCP or UDP? Simultaneous usage of TCP & Simultaneous usage of TCP &

UDPUDP Ex. MSN messenger, SkypeEx. MSN messenger, Skype See the open ports:See the open ports: http://http://

www.youtube.com/watch?vwww.youtube.com/watch?v=fuZylN8ZV_o=fuZylN8ZV_o

DNSDNS 53 (UDP)53 (UDP)

TFTPTFTP 69 (UDP)69 (UDP)

SNMPSNMP 161 (UDP)161 (UDP)

FTPFTP 20 &21 (TCP)20 &21 (TCP)

TelnetTelnet 23 (TCP)23 (TCP)

SMTPSMTP 25 (TCP)25 (TCP)

HTTPHTTP 80 (TCP)80 (TCP)

POP3POP3 110 (TCP)110 (TCP)

Port Numbers of some network ServersPort Numbers of some network Servers

Packet Loss and RetransmissionPacket Loss and Retransmission

Acknowledgement message (ACK)Acknowledgement message (ACK) Timer Timer Delay Delay RetransmissionRetransmission Concurrent working of application programs.Concurrent working of application programs. Duplicate packets problemDuplicate packets problem

IP (Internet Protocols)IP (Internet Protocols)

General Expression about IPGeneral Expression about IP The explanation of IPv4The explanation of IPv4 IPv4 address formatIPv4 address format The explanation of IPv6The explanation of IPv6 IPv6 address formatIPv6 address format Transition Duration to IPv6Transition Duration to IPv6 IPV4 vs. IPv6IPV4 vs. IPv6

General Expression about IPGeneral Expression about IP

What is IP?What is IP?

The Success of IP:The Success of IP: UniqueUnique LocatorLocator IdentifierIdentifier Handling heterogeneityHandling heterogeneity IP datagramIP datagram CompatibilityCompatibility Frame sizes and IPFrame sizes and IP

IPv4IPv4

IP and IPv4IP and IPv4 32 bit address32 bit address Solving need of IP Solving need of IP NAT (Network Address Translation), CIDRNAT (Network Address Translation), CIDR (Classless Inter-Domain (Classless Inter-Domain

Routing), DHCPRouting), DHCP What will happen in 2010s?What will happen in 2010s?

Deficiencies of IPv4Deficiencies of IPv4 Quality of serviceQuality of service SecuritySecurity Compatibility with electronic devicesCompatibility with electronic devices IPv4 Routing ProtocolsIPv4 Routing Protocols

IPv4 Address FormatIPv4 Address Format

Four numbers, each ranging Four numbers, each ranging from 0 to 255from 0 to 255

Ex. 147.132.42.18Ex. 147.132.42.18 Classes of networksClasses 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)

IPv6IPv6

Why IPv6 is needed?Why IPv6 is needed? Transition from IPv4 to IPv6Transition from IPv4 to IPv6 Changes in this transition durationChanges 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 programsProviding IPv6 support to application programs IOS (Interface Operating Systems) Nokia, Cisco,3ComIOS (Interface Operating Systems) Nokia, Cisco,3Com Ex. video: Ex. video: http://http://www.youtube.com/watch?vwww.youtube.com/watch?v=qsWNWm2O0_Q=qsWNWm2O0_Q

IPv6 Address FormatIPv6 Address Format

8 Pieces, 32 x hexadecimal numbers8 Pieces, 32 x hexadecimal numbers32*4=128 bits.32*4=128 bits.Ex: Ex: 3FFE:0B00:0000:0000:0000:0000:0000:00463FFE:0B00:0000:0000:0000:0000:0000:0046 0000:0000:0000:0000:0000:0000:0000:000000:0000:0000:0000:0000:0000:0000:00

0000Same with Same with 0:0:0:0:0:0:0:0 or :: 0:0:0:0:0:0:0:0 or :: 2010:0234:0000:0000:0067:0000:0000:002010:0234:0000:0000:0067:0000:0000:00

E2E2Same with Same with 2010:234:0:0:67:E2 2010:234:0:0:67:E2 40A1:0000:16FE:0000:0000:0C23:86E140A1:0000:16FE:0000:0000:0C23:86E1Same with Same with 40A1:0:16FE:0:0:C23:86E1 40A1:0:16FE:0:0:C23:86E1OrOr

40A1:0:16FE::C23:86E140A1:0:16FE::C23:86E1Only once usage of ::Only once usage of ::

Transition Duration to IPv6Transition Duration to IPv6

Changes in Client-Server SoftwareChanges in Client-Server Software Cost of changeCost of change Updating;Updating;

Client programs,Client programs, OSs,OSs, HardwareHardware

Network Connection device software updates.Network Connection device software updates.

IPv4 vs. IPv6IPv4 vs. IPv6

IPv4IPv4 IPV6IPV6

32 bit address32 bit address 128 bit address128 bit address

Uses base 10Uses base 10 Uses base 16Uses base 16

No abbreviationNo abbreviation Allow abbreviationAllow abbreviation

4 x 8 bits4 x 8 bits 8 x 16 bits8 x 16 bits

Pieces are separated with “.”Pieces are separated with “.” Pieces are separated with “:” Pieces are separated with “:”

127.0.0.1 is loopback address127.0.0.1 is loopback address 0:0:0:0:0:0:0:1 or ::1 is loopback 0:0:0:0:0:0:0:1 or ::1 is loopback addressaddress

Ex. video: http://www.youtube.com/watch?v=-ZW8v0zd6C0

SourcesSources

BOOKS:BOOKS: Bilgisayar Ağları ve Güvenliği – Alper ÖZBİLEN (Pusula Bilgisayar Ağları ve Güvenliği – Alper ÖZBİLEN (Pusula

Yayıncılık)Yayıncılık) IPv6 clearly explained- Pete LOSHINIPv6 clearly explained- Pete LOSHIN Internetworking with TCP/IP vol:III Client Server Internetworking with TCP/IP vol:III Client Server

Programming and ApplicationsProgramming and Applications

INTERNET Sources:INTERNET Sources: http://http://en.wikipedia.org/wiki/IP_addressen.wikipedia.org/wiki/IP_address www.youtube.comwww.youtube.com (videos) (videos)

Thank you for listening.Thank you for listening.

QuestionsQuestions