IT341 Chapter 10 - Application Layer
DNS Message Format
A - An end device IPv4 address NS - An authoritative name server AAAA - An end device IPv6 address (pronounced quad-A) MX - A mail exchange record
Server Message Block (SMB)
A client/server file sharing protocol that describes the structure of shared network resources, such as directories, files, printers, and serial ports.
BitTorrent
A peer-to-peer technology in which pieces of files are distributed to and from a collection of networked computers; used for distributing music and movies over the Internet
Host Config
BOOTP - Bootstrap Protocol DHCP - Dynamic Host Configuration Protocol
Client-Server Model
Client and server processes are considered to be in the application layer. Application layer protocols describe the format of the requests and responses between clients and servers.
Session Layer
Create and maintain dialogs between source and destination applications. Handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time.
DHCP Operations
DHCPDISCOVER - the client sends a query to the DHCP server to see if there are any IP addresses available DHCPOFFER - The server will send available IP address(es) to the client DHCPREQUEST - The client sends a request to the server asking for a lease of the IP address (usually the client will send a request to the first IP address offer given) DHCSPACK - Server sends an ack to the client and assigns the client the IP address
Name System
DNS - Domain Name system TCP, UDP client 53 Translates domain names, such as cicso.com into IP addresses.
Peer-To-Peer Network
Data is accessed from a peer device without the use of a dedicated server. Each device (known as a peer) can function as both a server and a client.
Application Layer Protocols
Domain Name System (DNS) Hypertext Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) Post Office Protocol (POP) Dynamic Host Configuration Protocol (DHCP) Internet Message Access Protocol (IMAP)
File Transfer
FTP - File Transfer Protocol TFTP - Trivial File Transfer Protocol
Presentation Layer 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.
HTTP Message Types
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 server, such as form data. PUT - This uploads resources or content to the web server, such as an image.
Web
HTTP - Hypertext Transfer Protocol HTTPS - HTTP Secure
Gnutella
Peer-to-peer applications based on *THIS* protocol, people can make files on their hard disks available to others for downloading.
SMTP - Simple Transfer Protocol POP3 - Post Office Protocol IMAP - Internet Message Access Protocol
SMB Functions
Start, authenticate, and terminate sessions. Control file and printer access. Allow an application to send or receive messages to or from another device.
HTTP Process
Step 1: Browser interprets the URL into: protocol or scheme, server name, specific file name. Step 2: The browser then checks with a name server to convert www.cisco.com into a numeric 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. Step 3: In response to the request, the server sends the HTML code for this web page to the browser. Step 4: The browser deciphers the HTML code and formats the page for the browser window.
DNS Process
Step 1: The user types an FQDN into a browser application Address field. Step 2: A DNS query is sent to the designated DNS server for the client computer. Step 3: The DNS server matches the FQDN with its IP address. Step 4: The DNS query response is sent back to the client with the IP address for the FQDN. Step 5: The client computer uses the IP address to make requests of the server.
POP3
TCP 110 Enables clients to retrieve email from a mail server Downloads the email to the local mail application of the client
IMAP
TCP 143 Enables clients to access email stored on a mail server Maintains email on the server
FTP
TCP 20 to 21 Sets rules that enable a user on one host to access and transfer files to and from another host over a network FTP is a reliable, connection-oriented, and acknowledged file delivery protocol Requires 2 connections between the client and the server, one for commands and replies, and the other for the file transfer.
SMTP
TCP 25 Enables clients to send email to a mail server Enables servers to send email to other servers
HTTP
TCP 80, 8080 A set of rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web
HTTPS
TCP, UDP 443 The browser uses encryption to secure HTTP communications Authenticates the website to which you are connecting your browser
DHCP
UDP client 68, server 67 Dynamically assigns IP addresses to be re-used when no longer needed.
BOOTP
UDP client 68, server 67 Enables a diskless workstation to discover its own IP address, the IP address of a server on the network, and a file to be loaded into memory to boost the machine. Being superseded by DHCP
TFTP
UDP client 69 A simple, connectionless file transfer protocol with best-effort, unacknowledged file delivery It uses less overhead than FTP
