Chapter - Application Layer Functionalityand Protocols CCNA Exploration 4.0 Overview • 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 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 Use network analysis tools to examine and explain how common user applications work H c vi n m ng Bách khoa - Website: www.bkacad.com Introduction • Explain that applications provide the means for generating and receiving data that can be transported on the network H c vi n m ng Bách khoa - Website: www.bkacad.com 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 was the descriptive network model that the ISO created It provided vendors with a set of standards that ensured greater compatibility and interoperability among various network technologies produced by companies around the world H c vi n m ng Bách khoa - Website: www.bkacad.com 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 H c vi n m ng Bách khoa - Website: www.bkacad.com The OSI Model H c vi n m ng Bách khoa - Website: www.bkacad.com OSI model • Explain the role of applications, services and protocols in converting • communication to data that can be transferred across the data network Application layer: It is the layer that provides the interface between the applications we use to communicate and the underlying network over which our messages are transmitted H c vi n m ng Bách khoa - Website: www.bkacad.com OSI model H c vi n m ng Bách khoa - Website: www.bkacad.com OSI model H c vi n m ng Bách khoa - Website: www.bkacad.com 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, Presentation and Session layers H c vi n m ng Bách khoa - Website: www.bkacad.com E-mail Services and SMTP/POP Protocols • • • 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 email server to the client (MUA) 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 H c vi n m ng Bách khoa - Website: www.bkacad.com FTP • • • • The File Transfer Protocol (FTP) is another commonly used Application layer protocol FTP was developed to allow for file transfers between a client and a server An FTP client is an application that runs on a computer that is used to push and pull files from a server running the FTP daemon (FTPd) 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 H c vi n m ng Bách khoa - Website: www.bkacad.com DHCP • • The Dynamic Host Confirmation Protocol (DHCP) service enables devices on a network to obtain IP addresses and other information from a DHCP server DHCP allows a host to obtain an IP address dynamically when it connects to the network H c vi n m ng Bách khoa - Website: www.bkacad.com Why Use DHCP? DHCP reduces the complexity and amount of administrative work by using automatic TCP/IP configuration Manual TCP/IP Configuration Automatic TCP/IP Configuration IP addresses are entered manually on each client computer IP addresses are supplied automatically to client computers Possibility of entering incorrect or invalid IP address Ensures that clients always use correct configuration information Incorrect configuration can lead to communication and network issues Client configuration is updated automatically to reflect changes in network structure Administrative overload on networks where computers are frequently moved Eliminates a common source of network problems H c vi n m ng Bách khoa - Website: www.bkacad.com What Are DHCP Scopes? A scope is a range of IP addresses that are available to be leased DHCP Server LAN A LAN B Scope A Scope B Scope Properties • Network ID • Subnet mask • Network IP • Lease duration • Scope name • Router • Exclusion range address range H c vi n m ng Bách khoa - Website: www.bkacad.com DHCP • • The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when the client is powered on DHCP Packet: – DHCP DISCOVER – DHCP OFFER – DHCP REQUEST – DHCP ACK H c vi n m ng Bách khoa - Website: www.bkacad.com How the DHCP Operation DHCP Server2 DHCP Server1 DHCP Client DHCP client broadcasts a DHCPDISCOVER packet DHCP servers broadcast a DHCPOFFER packet DHCP client broadcasts a DHCPREQUEST packet DHCP Server1 broadcasts a DHCPACK packet H c vi n m ng Bách khoa - Website: www.bkacad.com 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 H c vi n m ng Bách khoa - Website: www.bkacad.com 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 H c vi n m ng Bách khoa - Website: www.bkacad.com P2P Services and Gnutella Protocol • • • Many P2P applications 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 H c vi n m ng Bách khoa - Website: www.bkacad.com 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 H c vi n m ng Bách khoa - Website: www.bkacad.com 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 H c vi n m ng Bách khoa - Website: www.bkacad.com Labs H c vi n m ng Bách khoa - Website: www.bkacad.com Summary H c vi n m ng Bách khoa - Website: www.bkacad.com H c vi n m ng Bách khoa - Website: www.bkacad.com ... - Website: www.bkacad.com 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... vi n m ng Bách khoa - Website: www.bkacad.com Peer-to-Peer Networking and Applications (p2p) Peer-to-Peer Applications • A peer-to-peer application (P2P), unlike a peer-to-peer network, allows... 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