Chương 3 - Lớp ứng dụng giao thức CCNA ppsx

• Describe how the functions of the three upper OSI model layers provide network services to end user applications.. • Describe how the TCP/IP Application Layer protocols provide the s

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Chapter 3 - Application Layer Functionalityand Protocols

CCNA Exploration 4.0

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• Describe how the functions of the three upper OSI model layers

provide network services to end user applications.

• Describe how the TCP/IP Application Layer protocols provide the

services specified by the upper layers of the OSI model.

• Define how people use the Application Layer to communicate across the information network.

• Describe the function of well-known TCP/IP applications, such as the

• Describe the function of well-known TCP/IP applications, such as the World Wide Web and email, and their related services (HTTP, DNS, SMB, DHCP, STMP/POP, and Telnet).

• Describe file-sharing processes that use peer-to-peer applications and the Gnutella protocol.

• Explain how protocols ensure services running on one kind of device can send to and receive data from many different network devices.

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OSI model

• To address the problem of network incompatibility, the International

Organization for Standardization (ISO) researched networking models like Digital Equipment Corporation net (DECnet), Systems Network Architecture (SNA), and TCP/IP in order to find a generally applicable set of rules for all networks

• Using this research, the ISO created a network model that helps vendors create networks that are compatible with other networks

• The Open System Interconnection (OSI) reference model released in 1984

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The OSI Model

• Initially the OSI model was designed by the International Organization for

Standardization (ISO) to provide a framework on which to build a suite of open systems protocols

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The OSI Model

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OSI model

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OSI model

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OSI and TCP/IP Model

• Functionality of the TCP/IP application layer protocols fit roughly into the framework of the top three layers of the OSI model: Application,

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• The Presentation layer has three primary functions:

data from the source device can be interpreted by the appropriate application on the destination device.

by the destination device.

upon receipt by the destination.

Example : QuickTime, Motion Picture Experts Group (MPEG),

Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG)…

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The Session Layer

• Functions at this layer create and maintain dialogs between source and destination applications.

• The Session layer handles the exchange of information to initiate

dialogs, keep them active, and to restart sessions that are disrupted or dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time

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Application Layer Protocols

• These protocols specify the format and control information necessary for many of the common Internet communication functions Among these TCP/IP protocols are:

– Domain Name Service Protocol (DNS).

– Hypertext Transfer Protocol (HTTP).

– Simple Mail Transfer Protocol (SMTP)

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Application Layer Software

• The functions associated with the Application layer protocols enable our human network to interface with the underlying data network.

• Within the Application layer, there are two forms of software programs

or processes that provide access to the network: applications and

services

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User applications, Services, and Application Layer Protocols

• The Application layer uses protocols that are implemented within

applications and services.

• While applications provide people a way to create messages and

application layer services establish an interface to the network,

protocols provide the rules and formats that govern how data is treated.

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Application Layer Protocol Functions

• Application layer protocols are used by both the source

and destination devices during a communication session

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The Client-Server Model

• In the client/server model, the device requesting the information is called a client and the device responding to the request is called a

Application layer.

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user account information

to verify if the user has

permission to access the

requested data or to use

a particular operation

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Application Layer Services and Protocols

• A single application may employ many different supporting Application layer services.

• Additionally, servers typically have multiple clients requesting

information at the same time.

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Peer-to-Peer Networking and Applications (p2p)

The Peer-to-Peer Model

• Peer-to-peer networking involves two distinct forms: peer-to-peer network

design and peer-to-peer applications (P2P) Both forms have similar features but in practice work very differently

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Peer-to-Peer Networking and Applications (p2p)

Peer-to-Peer Applications

• A peer-to-peer application (P2P), unlike a peer-to-peer network, allows a

device to act as both a client and a server within the same communication

• In this model, every client is a server and every server a client Both can initiate

a communication and are considered equal in the communication process

• Peer-to-peer applications can be used on peer-to-peer networks, client/server networks, and across the Internet

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Application Layer Protocols and Services Examples

• Now that we have a better understanding of how applications provide

an interface for the user and provide access to the network, we will take a look at some specific commonly used protocols.

• Some of these services are:

– Domain Name System (DNS) - TCP/UDP Port 53

– Hypertext Transfer Protocol (HTTP) - TCP Port 80

– Simple Mail Transfer Protocol (SMTP) - TCP Port 25

– Post Office Protocol (POP) - UDP Port 110

– Telnet - TCP Port 23

– Dynamic Host Configuration Protocol - UDP Port 67

– File Transfer Protocol (FTP) - TCP Ports 20 and 21

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DNS Services and Protocol

• A domain naming system was developed in order to associate the

contents of the site with the address of that site The Domain Name System (DNS) is a system used on the Internet for translating names

of domains and their publicly advertised network nodes into IP

addresses

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DNS Services and protocol

• The Domain Name System (DNS) was created for domain name to

address resolution for these networks DNS uses a distributed set of servers to resolve the names associated with these numbered

addresses

names with the required numeric network address.

• DNS protocol communications use a single format called a message.

• DNS is used for all types of client queries and server responses, error messages, and the transfer of resource record information between

servers.

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DNS - Example

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DNS - Example

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DNS - Example

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DNS - Example

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DNS - Example

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DNS - Example

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DNS Services and Protocol

• The DNS server stores different types of resource records used to resolve names These records contain the name, address, and type of record.

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DNS Services and protocol

• When configuring a network device, we generally provide one or more

DNS Server addresses that the DNS client can use for name

resolution

• Computer operating systems also have a utility called nslookup that allows the user to manually query the name servers to resolve a given host name This utility can also be used to troubleshoot name

resolution issues and to verify the current status of the name servers

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WWW Service and HTTP

• When a web address (or URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server using the HTTP protocol

• URLs (or Uniform Resource Locator) and URIs (Uniform Resource Identifier) are the names most people associate with web addresses

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• In order to access the content, web clients make connections to the server and request the desired resources The server replies with the resources and, upon receipt, the browser interprets the data and

presents it to the user.

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• Browsers can interpret and present many data types, such as plain text

or H yper t ext M arkup L anguage (HTML, the language in which web

pages are constructed) Other types of data, however, may require

another service or program, typically referred to as plug-ins or add-ons

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• HTTP specifies a request/response protocol When a client, typically a web browser, sends a request message to a server, the HTTP protocol defines the message types the client uses to request the web page and also the message types the server uses to respond The three common message types are GET, POST and PUT

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E-mail Services and SMTP/POP Protocols

• E-mail, the most popular network service and run on a computer or other end device, e-mail requires several applications and services

• POP/SMTP define client/server processes

• Mail User Agent (MUA): allows messages to be sent and places received messages into the client's mailbox, both of which are distinct processes MUA include: POP and SMTP

• POP: used to receive e-mail messages from an e-mail server

• SMTP: used to send e-mail from either a client or a server uses message

formats and command strings

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E-mail Server Processes - MTA and MDA

• The e-mail server operates two separate processes:

– M ail T ransfer A gent (MTA).

– M ail D elivery A gent (MDA).

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• We see that the Mail Delivery Agent (MDA) accepts a piece of e-mail from a Mail Transfer Agent (MTA) and performs the actual delivery

• The MDA receives all the inbound mail from the MTA and places it into the appropriate users' mailboxes

• The MDA can also resolve final delivery issues, such as virus scanning, spam filtering, and return-receipt handling

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• POP and POP3 (Post Office Protocol, version 3) are inbound mail delivery

protocols and are typical client/server protocols They deliver e-mail from the mail server to the client (MUA)

e-• The MDA listens for when a client connects to a server Once a connection is established, the server can deliver the e-mail to the client

• Some of the commands specified in the SMTP protocol are: HELO, EHLO,

MAIL FROM, RCPT TO, DATA

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• The client establishes the first connection to the server on TCP port 21 The client establishes the second connection to the server over TCP port 20

• The file transfer can happen in either direction

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Why Use DHCP?

DHCP reduces the complexity and amount of administrative work by using automatic TCP/IP configuration

Manual TCP/IP Configuration

IP addresses are entered

manually on each client computer

Automatic TCP/IP Configuration

IP addresses are supplied automatically to client computers

Possibility of entering incorrect or

invalid IP address

Incorrect configuration can lead

to communication and network

in network structure Eliminates a common source of network problems

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What Are DHCP Scopes?

A scope is a range of IP addresses that are available to be leased

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How the DHCP Operation

DHCP DHCP

DHCP Server2

DHCP client broadcasts a DHCPDISCOVER packet

11

DHCP servers broadcast a DHCPOFFER packet

22

DHCP Client DHCP

Server1

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File Sharing Services and SMB Protocol

• The Server Message Block (SMB) is a client/server file sharing protocol

• Unlike the file sharing supported by FTP, clients establish a long term

connection to servers Once the connection is established, the user of the client can access the resources on the server as if the resource is local to the client host

• SMB file-sharing and print services have become the mainstay of Microsoft networking

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File Sharing Services and SMB Protocol

• The SMB protocol describes file system access and how clients can make

requests for files All SMB messages share a common format This format uses

a fixed-sized header followed by a variable-sized parameter and data

component

• SMB messages can:

– Start, authenticate, and terminate sessions

– Control file and printer access

– Allow an application to send or receive messages to or from another device

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P2P Services and Gnutella Protocol

• Many P2P applications do not use a central database to record all the files available on the peers

• When a user is connected to a Gnutella service, the client applications will

search for other Gnutella nodes to connect to These nodes handle queries for resource locations and replies to those requests

• The Gnutella protocol defines five different packet types: ping, pong, query, query hit, push

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Telnet Services and Protocol

• Telnet provides a standard method of emulating text-based terminal devices

over the data network Both the protocol itself and the client software that implements the protocol are commonly referred to as Telnet

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Telnet Services and Protocol

• Telnet is a client/server protocol and it specifies how a VTY session is

established and terminated

• Each Telnet command consists of at least two bytes The first byte is a special character called the Interpret as Command (IAC) character

• If security is a concern, the Secure Shell (SSH) protocol offers an alternate and secure method for server access

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Labs

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Tiêu đề	Chương 3 - Lớp ứng dụng giao thức CCNA ppsx
Trường học	Học viện Mạng Bách Khoa
Chuyên ngành	Networking / Computer Networks
Thể loại	Giáo trình / Tài liệu học tập
Năm xuất bản	N/A
Thành phố	Unknown

Định dạng
Số trang	54
Dung lượng	2,7 MB