Network Services and Applications


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Network Services and Applications

  1. 1. Chapter 9 Network Services and Applications
  2. 2. Topics <ul><li>Understanding Network Services </li></ul><ul><li>File Transfer Protocol (FTP) </li></ul><ul><li>Telnet </li></ul><ul><li>Trivial File Transfer Protocol (TFTP) </li></ul><ul><li>Domain Name System (DNS) </li></ul><ul><li>Dynamic Host Configuration Protocol (DHCP) </li></ul><ul><li>Simple Network Management Protocol (SNMP) </li></ul><ul><li>Electronic Mail (E-mail) </li></ul><ul><li>World Wide Web </li></ul><ul><li>Remote Procedure Call (RPC) and Middleware </li></ul>
  3. 3. Understanding Network Services <ul><li>Services help the operating system and applications communicate with each other </li></ul><ul><li>This is done through TCP and UDP acting as port managers for the applications and services that are in the top layer </li></ul>
  4. 4. Understanding Network Services <ul><li>In order to establish a connection, a machine needs to know the IP address and port number on which the application communicates </li></ul><ul><li>The destination port number is placed in the header and is used to pass traffic to the correct application </li></ul><ul><li>There are 65,535 ports that can be accessed on a machine </li></ul>
  5. 5. Understanding Network Services <ul><li>The well-known ports are those from 0 through 1023 </li></ul><ul><li>These can be used only by system processes </li></ul><ul><li>Ports 1024 through 49151 are registered </li></ul><ul><li>Ports 49152 through 65535 are dynamic or private </li></ul>
  6. 6. File Transfer Protocol (FTP) <ul><li>File Transfer Protocol (FTP) allows a person to transfer files between two computers </li></ul><ul><li>This is usually a client and a server, while being connected to the Internet </li></ul><ul><li>FTP makes it possible to move one or more files between computers with security and data integrity controls appropriate for the Internet </li></ul>
  7. 7. File Transfer Protocol (FTP) <ul><li>FTP is a TCP-based service that utilizes a data port and a control port </li></ul><ul><li>Traditionally these are port 21 for the command port and port 20 for the data port </li></ul><ul><li>In active mode, the FTP client doesn't make the actual connection to the data port of the server; it simply states what port it is listening on and the server connects to the specified port on the client </li></ul>
  8. 8. File Transfer Protocol (FTP) <ul><li>In passive mode, the client initiates all connections to the server </li></ul><ul><li>The client opens two random unprivileged ports locally </li></ul><ul><li>This is useful when trying to provide FTP connections through firewalls </li></ul><ul><li>Most browsers only support passive mode </li></ul>
  9. 9. File Transfer Protocol (FTP) <ul><li>In standard routing, the route table is consulted every time a frame is received, and so plays a fundamental role in the proper delivery of data </li></ul><ul><li>A routing table only maintains the best possible route to a destination, not all possible routes </li></ul>
  10. 10. File Transfer Protocol (FTP) <ul><li>FTP is used with your Web browser or through a command line prompt </li></ul><ul><li>Programs such as Fetch, Cute FTP, and WS_FTP also are used for transferring and managing files </li></ul><ul><li>TRICKLE provides an alternative to FTP </li></ul><ul><li>It distributes files upon request or by subscription </li></ul>
  11. 11. Telnet <ul><li>Telecommunications Network or Telnet is a protocol that provides a way for clients to connect to servers on the Internet </li></ul><ul><li>The Telnet application is built over TCP/IP and provides the local machine with the means to emulate a terminal session compatible with the remote computer </li></ul><ul><li>It allows the user to create a connection and send commands and instructions interactively to the remote machine </li></ul>
  12. 12. Telnet <ul><li>The Telnet command is similar to the FTP command </li></ul><ul><li>Telnet has no graphical user interface (GUI). </li></ul><ul><li>The Telnet TCP connection is established between a random unprivileged port on the client and port 23 on the server </li></ul><ul><li>Because a TCP connection is full-duplex and identified by the pair of ports, the server can engage in many simultaneous connections involving its port 23 and different random unprivileged ports on the client </li></ul>
  13. 13. Trivial File Transfer Protocol (TFTP) <ul><li>Trivial File Transfer Protocol (TFTP) is a simple form of the File Transfer Protocol that uses the User Datagram Protocol (UDP) </li></ul><ul><li>It is often used for booting or loading programs on diskless workstations </li></ul><ul><li>It does not guarantee delivery and provides no security features </li></ul>
  14. 14. Trivial File Transfer Protocol (TFTP) <ul><li>TFTP provides its own reliable delivery using a simple stop-and-wait acknowledgment system </li></ul><ul><li>Its services run at port 69 </li></ul><ul><li>TFTP issues read and write requests to the remote machine </li></ul><ul><li>It can be implemented within the firmware on network devices that do not contain hard drive </li></ul>
  15. 15. Domain Name System (DNS) <ul><li>Domain Name System (DNS) takes the names we type into a Web browser and resolves them to a proper network address </li></ul><ul><li>DNS consists of name servers and resolvers </li></ul><ul><li>Domain name servers store authoritative data about sections of a distributed database and respond to browser requests by supplying name-to-address conversions </li></ul>
  16. 16. Domain Name System (DNS) <ul><li>There are several implementations of DNS </li></ul><ul><li>One the most popular is called Berkeley Internet Name Domain (BIND) </li></ul><ul><li>BIND is an Internet name server for Unix operating systems </li></ul><ul><li>Because most of the development on the DNS protocols is based on this code, the BIND name server is the most widely used on the Internet </li></ul>
  17. 17. Domain Name System (DNS) <ul><li>The last portion of a host name, such as .com, is the top-level domain to which the host belongs </li></ul><ul><li>Within every top-level domain there is a second-level domain, such as </li></ul><ul><li>The fully qualified domain name (FQDN) consists of the host name appended to the computer’s domain </li></ul>
  18. 18. Domain Name System (DNS) <ul><li>Name servers do not have complete information, so often it is necessary to obtain information from more than one server to resolve a query </li></ul><ul><li>If the name server is unfamiliar with the domain name, the resolver will ask a server further up the tree </li></ul><ul><li>It will continue to forward up until it finds one that knows the information </li></ul>
  19. 19. Domain Name System (DNS) <ul><li>At the top of the DNS database tree are root name servers, which contain pointer records to master name servers for each of the top-level domains </li></ul><ul><li>Each name server manages a group of records called a zone </li></ul><ul><li>Zones are set up to help resolve names more easily and for replication purposes </li></ul>
  20. 20. Domain Name System (DNS) <ul><li>DNS zones specify the domain name boundary in which a DNS server has authority to perform name translations </li></ul><ul><li>The .arpa domain maintains a reverse list of IP addresses to Internet addresses </li></ul><ul><li>The IP addresses in the .arpa domain are listed in reverse order </li></ul><ul><li>You can either administer your own DNS servers or have an Internet service provider (ISP) do it for you </li></ul>
  21. 21. Dynamic Host Configuration Protocol (DHCP) <ul><li>DHCP is an extension of the Bootstrap Protocol (BOOTP) </li></ul><ul><li>DHCP has capabilities for assigning clients a network address for a fixed period of time </li></ul><ul><li>It can allow for reassignment of network addresses to different clients </li></ul><ul><li>DHCP provides the means for a client to acquire all of the IP configuration parameters that it needs in order to operate </li></ul>
  22. 22. Dynamic Host Configuration Protocol (DHCP) <ul><li>The most important piece of data distributed by DHCP is the IP address </li></ul><ul><li>DHCP supports three methods of IP address allocation: </li></ul><ul><ul><li>Manual </li></ul></ul><ul><ul><li>Automatic </li></ul></ul><ul><ul><li>Dynamic </li></ul></ul><ul><li>Dynamic addressing simplifies network administration </li></ul>
  23. 23. Dynamic Host Configuration Protocol (DHCP) <ul><li>In dynamic addressing, the IP addresses are kept track of by the software rather than an administrator </li></ul><ul><li>It is the only one of the three methods that allows the server to automatically reuse an address that is no longer needed </li></ul><ul><li>It is useful for assigning an address to a client that will be connected to the network only temporarily </li></ul>
  24. 24. Dynamic Host Configuration Protocol (DHCP) <ul><li>DHCP is not supported by all operating systems </li></ul><ul><li>It can only work with TCP/IP </li></ul><ul><li>It cannot work with AppleTalk or IPX/SPX because it is tied to IP </li></ul><ul><li>These protocols have no need for DHCP because they have their own automated mechanisms for assigning network addresses </li></ul>
  25. 25. Dynamic Host Configuration Protocol (DHCP) <ul><li>When a DHCP device attaches itself to the network for the first time, it broadcasts a DHCPDISCOVER packet using UDP on port 67 </li></ul><ul><li>All DHCP servers on the local segment will broadcast a DHCPOFFER packet that contains proper configuration for the client based on parameters that are specified in the DHCP server on port 68 </li></ul><ul><li>The client may receive multiple DHCPOFFER packets from any number of servers </li></ul>
  26. 26. Dynamic Host Configuration Protocol (DHCP) <ul><li>The client then broadcasts a DHCPREQUEST packet that identifies the server address (siaddr) and IP address (yiaddr) offer that it has selected </li></ul><ul><li>The server then returns a DHCPACK that sends the client all the requested parameters </li></ul><ul><li>Once the client has the lease, it must be renewed prior to the expiration </li></ul><ul><li>Generally, a client attempts to renew its lease halfway through the lease process </li></ul>
  27. 27. Simple Network Management Protocol (SNMP) <ul><li>SNMP is part of the TCP/IP protocol suite </li></ul><ul><li>It is an Application layer protocol that is used to exchange management information between network devices </li></ul><ul><li>SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth </li></ul>
  28. 28. Simple Network Management Protocol (SNMP) <ul><li>SNMP management infrastructure consists of three main components: </li></ul><ul><ul><li>SNMP managed node </li></ul></ul><ul><ul><li>SNMP agent </li></ul></ul><ul><ul><li>SNMP network management station </li></ul></ul><ul><li>Three versions of SNMP exist </li></ul><ul><li>SNMPv3 addresses major security and authentication concerns of SNMPv1 and SNMPv2 </li></ul>
  29. 29. Simple Network Management Protocol (SNMP) <ul><li>All agents and management stations must belong to an SNMP community </li></ul><ul><li>SNMP and management stations that belong to the same community can accept messages from each other </li></ul><ul><li>The Remote Monitoring (RMON) specification can be considered an extension to the SNMP standard </li></ul><ul><li>Cisco Systems includes SNMP and RMON functionality in its software </li></ul>
  30. 30. Electronic Mail (E-mail) <ul><li>Electronic mail (e-mail) was one of the first Internet applications </li></ul><ul><li>E-mail uses a store-and-forward method of transmission </li></ul><ul><li>The messages are stored in an electronic mailbox </li></ul><ul><li>When a user logs on, the messages are downloaded onto the workstation </li></ul>
  31. 31. Electronic Mail (E-mail) <ul><li>Windows, Linux, and NetWare all have their own versions of e-mail software </li></ul><ul><li>Besides message delivery, many e-mail products offer: </li></ul><ul><ul><li>address books for storing contact information </li></ul></ul><ul><ul><li>filtering software for eliminating junk mail </li></ul></ul><ul><ul><li>the ability to make distribution lists </li></ul></ul>
  32. 32. Electronic Mail (E-mail) <ul><li>Multipurpose Internet Mail Extensions (MIME) is the standard that defines the format of text messages </li></ul><ul><li>The basic idea behind this standard is that the content of e-mail messages is logically divided into two pieces: </li></ul><ul><ul><li>the header </li></ul></ul><ul><ul><li>the body </li></ul></ul>
  33. 33. Electronic Mail (E-mail) <ul><li>Several different formats can be chosen for the e-mail body besides basic text formatting: </li></ul><ul><ul><li>HTML supports text formatting, color and background images, horizontal lines, alignments, HTML styles, and Web pages </li></ul></ul><ul><ul><li>MIME HTML (MHTML) enables full Web pages to be sent inside e-mail messages </li></ul></ul><ul><ul><li>Plain Text does not contain any formatting </li></ul></ul>
  34. 34. Electronic Mail (E-mail) <ul><li>Several different formats can be chosen for the e-mail body besides basic text formatting: </li></ul><ul><ul><li>Rich Text supports text formatting, bullets, color, and alignment </li></ul></ul><ul><ul><li>S/MIME helps ensure the security of e-mail by enabling users to digitally encrypt and sign messages </li></ul></ul><ul><ul><li>Pretty Good Privacy (PGP) allows messages to be digitally signed and encrypted </li></ul></ul>
  35. 35. Electronic Mail (E-mail) <ul><li>The standard protocols used for sending Internet e-mail are: </li></ul><ul><ul><li>Simple Mail Transfer Protocol (SMTP) </li></ul></ul><ul><ul><li>and Post Office Protocol (POP) </li></ul></ul><ul><li>Post Office Protocol (POP) is used to retrieve e-mail from a mail server </li></ul><ul><li>IMAP4 deals strictly with the client-side handling of e-mail </li></ul>
  36. 36. Electronic Mail (E-mail) <ul><li>IMAP4 allows client computers to work with messages stored in mailboxes on remote mail servers </li></ul><ul><li>SMTP works above the TCP/IP layer on port 25 </li></ul><ul><li>SMTP is used as a transport protocol for sending e-mail server-to-server </li></ul>
  37. 37. World Wide Web <ul><li>The Web consists of: </li></ul><ul><ul><li>Your computer </li></ul></ul><ul><ul><li>Web browser software </li></ul></ul><ul><ul><li>A connection to an ISP </li></ul></ul><ul><ul><li>Servers that host data </li></ul></ul><ul><ul><li>Routers or switches that direct the flow of information </li></ul></ul><ul><li>Based on a client/server architecture </li></ul>
  38. 38. World Wide Web <ul><li>The language used to format pages on the Web is called the Hypertext Markup Language (HTML) </li></ul><ul><li>HTML is a document markup language that includes a set of tags for defining the format and style of documents </li></ul><ul><li>Web pages are written in HTML so that Web browsers can understand them </li></ul>
  39. 39. World Wide Web <ul><li>Web clients and servers use Hypertext Transfer Protocol (HTTP) to communicate with each other </li></ul><ul><li>HTTP is an application-level stateless protocol </li></ul><ul><li>It only defines what the browser and Web server say to each other </li></ul><ul><li>Each command is executed independently </li></ul>
  40. 40. World Wide Web <ul><li>A Web browser is the client software that allows you to access and view any document on the Web </li></ul><ul><li>A Web page is accessed by typing a Uniform Resource Locator (URL) into the address bar of the browser </li></ul><ul><li>Every Web site and every Web page has a unique URL </li></ul>
  41. 41. World Wide Web <ul><li>In addition to HTML the following markup languages exist: </li></ul><ul><ul><li>SGML </li></ul></ul><ul><ul><li>XML </li></ul></ul><ul><ul><li>XHTML </li></ul></ul><ul><ul><li>DHTML </li></ul></ul><ul><ul><li>RDF </li></ul></ul><ul><ul><li>DAML </li></ul></ul>
  42. 42. Remote Procedure Call (RPC) and Middleware <ul><li>Remote Procedure Call (RPC) is a protocol that a program can use to request a service from a program located on another computer in a network </li></ul><ul><li>It uses the client/server model </li></ul><ul><li>The requesting program is a client and the service program is the server </li></ul><ul><li>The remote procedure call is intended to act across the network transparently </li></ul>
  43. 43. Remote Procedure Call (RPC) and Middleware <ul><li>RPC is transport independent </li></ul><ul><li>It allows the application to use a variety of transports </li></ul><ul><li>RPC does not care how a message is passed from one process to another </li></ul><ul><li>RPC deals only with specification and interpretation of messages </li></ul>
  44. 44. Remote Procedure Call (RPC) and Middleware <ul><li>Middleware is software that connects applications, allowing them to exchange data </li></ul><ul><li>It is a general term for any programming that provides messaging services so that two separate, and often already existing applications, can communicate </li></ul><ul><li>It is software that consists of a set of services that allow multiple processes running on one or more machines to interact across a network </li></ul>