CCNA1_Mod15_Application_Layer v1.pdf

Application Layer The upper three layers of the OSI model (application, presentation, and session) define functions of the TCP/IP application layer. The application layer provides the interface between the applications used to communicate, and the underlying network over which messag...

Application Layer The upper three layers of the OSI model (application, presentation, and session) define functions of the TCP/IP application layer. The application layer provides the interface between the applications used to communicate, and the underlying network over which messages are transmitted. Some of the most widely known application layer protocols include HTTP, FTP, TFTP, IMAP and DNS. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1 Presentation and Session Layer The presentation layer has three primary functions: Formatting, or presenting, data at the source device into a compatible format for receipt by the destination device Compressing data in a way that can be decompressed by the destination device Encrypting data for transmission and decrypting data upon receipt The session layer functions: It creates and maintains dialogs between source and destination applications. It handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 TCP/IP Application Layer Protocols The TCP/IP application protocols specify the format and control information necessary for many common internet communication functions. Application layer protocols are used by both the source and destination devices during a communication session. Name System Host Config Web DNS - Domain Name System DHCP - Dynamic Host HTTP - Hypertext Transfer (or Service) Configuration Protocol Protocol Translates domain names, Dynamically assigns IP A set of rules for exchanging such as cisco.com, into IP addresses to be re-used text, graphic images, sound, addresses. when no longer needed video, and other multimedia files on the World Wide Web © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 Hypertext Transfer Protocol  When a web address or Uniform Resource Locator (URL) is typed into a web browser, the web browser establishes a connection to the web service.  The web service is running on the server that is using the HTTP protocol.  To better understand how the web browser and web server interact, examine how a web page is opened in a browser in the following steps: Step 1 The browser interprets the three parts of the URL: http (the protocol or scheme) www.cisco.com (the server name) index.html (the specific filename requested) © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 Hypertext Transfer Protocol Step 2 Step 3 The browser then checks with a In response to the request, the server name server to convert sends the HTML code for this web page www.cisco.com into a numeric to the browser. IP address, which it uses to connect to the server. The client initiates an HTTP request to a server by sending a GET request to the server and asks for the index.html file. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 HTTP and HTTPS  HTTP is a request/response protocol that specifies the message types used for that communication.  The three common message types are GET, POST, and PUT: GET - This is a client request for data. A client (web browser) sends the GET message to the web server to request HTML pages. POST - This uploads data files to the web Note: HTTP is not a secure protocol. For server, such as form data. secure communications sent across the PUT - This uploads resources or content to internet, HTTPS should be used. the web server, such as an image. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 Email Protocols  Email is a store-and-forward method of sending, storing, and retrieving electronic messages across a network.  Email messages are stored in databases on mail servers.  Email clients communicate with mail servers to send and receive email.  The email protocols used for operation are: Simple Mail Transfer Protocol (SMTP) – used to send mail. Post Office Protocol (POP) & IMAP – used for clients to receive mail. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 Domain Name Service Domain names were created to convert the numeric IP addresses into a simple, recognizable name. Fully-qualified domain names (FQDNs), such as http://www.cisco.com, are much easier for people to remember than 198.133.219.25. The DNS protocol defines an automated service that matches resource names with the required numeric network address. It includes the format for queries, responses, and data. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 DNS Hierarchy DNS uses a hierarchical system to create a database to provide name resolution. Each DNS server maintains a specific database file and is only responsible for managing name-to-IP mappings for that small portion of the entire DNS structure. When a DNS server receives a request for a name translation that is not within its DNS zone, the DNS server forwards the request to another DNS server within the proper zone for translation. Examples of top-level domains:.com - a business or industry.org - a non-profit organization.au - Australia © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9 Dynamic Host Configuration Protocol The Dynamic Host Configuration Protocol (DHCP) for IPv4 service automates the assignment of IPv4 addresses, subnet masks, gateways, and other IPv4 networking parameters. When a host connects to the network, the DHCP server is contacted, and an address is requested. The DHCP server chooses an address from a configured range of addresses called a pool and assigns (leases) it to the host. DHCP for IPv6 (DHCPv6) provides similar services for IPv6 clients. However, DHCPv6 does not provide a default gateway address. This can only be obtained dynamically from the Router Advertisement message of the router. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10 File Transfer Protocol FTP was developed to allow for data transfers between a client and a server. An FTP client is an application which runs on a computer that is being used to push and pull data from an FTP server. Step 1 - The client establishes the first connection to the server for control traffic using TCP port 21. Step 2 - The client establishes the second connection to the server for the actual data transfer using TCP port 20. This connection is created every time there is data to be transferred. Step 3 - The data transfer can happen in either direction. The client can download (pull) data from the server, or the client can upload (push) data to the server. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 Server Message Block  The Server Message Block (SMB) is a client/server, request- response file sharing protocol.  Servers can make their own resources available to clients on the network.  Three functions of SMB messages: Start, authenticate, and terminate sessions Control file and printer access Allow an application to send or receive messages to or from another device  Unlike the file sharing supported by FTP, clients establish a long-term connection to servers. After the connection is established, the user of the client can access the resources on the server as though the resource is local to the client host. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12