Network Services and Applications
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    Network Services and Applications Network Services and Applications Presentation Transcript

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