Need only question 2.Need each step to do this problem. (Need steps to set up an SMTP server. Need link to install SMTP server. Code to send EMAIL .)
CNT 5008 – Fall 2021 - Homework 2 Due: September 27, 2021 Instructions: • Submit your answers in the form of a single document file • Remember that the homework is individual work. • Notice that points add up to 17, with 14 + 3 bonus points Problem 1 (3 points) – Setting up your computer for RAW TCP. Problems 2 and 3 require you to do raw TCP connection. You can do this in several ways, here are several: • Use Linux, and install telnet if not coming with it by default. • Use Linux subsystem for Windows, install Ubuntu, and then telnet. • Use Telnet in Windows (it is part of the system but you need to install it separately) • Use the raw mode of the program Putty in Windows. • Raw sockets in python • Raw sockets in C Research these options and configure your computer such that you can achieve Problems 2 and 3. Describe your research, the configation choices you made and possible challenges you encountered. Problem 2 (7 points): Access the UCF computer science web site by directly using the HTTP protocol directly entered into one of the options above. See Slide 33 in the application layer powerpoint slides. Use other resources in the book and internet as needed. Log the sessions and attach it to your answer. Describe any problem you had and any research you had to do. Problem 3 (7 points): Research and find an SMTP server you can access. Due to spam and security concerns, there are less number of freely available SMTP servers than they used to be. Please google “smtp server for testing”. Alternatively, you can use something like Papercut (https://github.com/ChangemakerStudios/Papercut- SMTP) or mailtrap / sendria (https://github.com/msztolcman/sendria ). Send yourself an email by directly using the SMTP protocol. See Slide 50 in the application layer powerpoint slides. Use other resources in the book and internet as needed. Log the sessions and attach it to your answer. Describe any problem you had and any research you had to do. https://github.com/ChangemakerStudios/Papercut-SMTP https://github.com/ChangemakerStudios/Papercut-SMTP https://github.com/msztolcman/sendria 3rd Edition: Chapter 2 Computer Networking: A Top Down Approach A note on the use of these Powerpoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996-2016 J.F Kurose and K.W. Ross, All Rights Reserved 7th edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 Chapter 2 Application Layer Application Layer 2-1 Application Layer 2-2 Chapter 2: outline 2.1 principles of network applications 2.2 Web and HTTP 2.3 electronic mail SMTP, POP3, IMAP 2.4 DNS 2.5 P2P applications 2.6 video streaming and content distribution networks 2.7 socket programming with UDP and TCP 2 Application Layer 2-3 Chapter 2: application layer our goals: conceptual, implementation aspects of network application protocols transport-layer service models client-server paradigm peer-to-peer paradigm content distribution networks learn about protocols by examining popular application-level protocols HTTP FTP SMTP / POP3 / IMAP DNS creating network applications socket API 3 Application Layer 2-4 Some network apps e-mail web text messaging remote login P2P file sharing multi-user network games streaming stored video (YouTube, Hulu, Netflix) voice over IP (e.g., Skype) real-time video conferencing social networking search … … 4 Application Layer 2-5 Creating a network app write programs that: run on (different) end systems communicate over network e.g., web server software communicates with browser software no need to write software for network-core devices network-core devices do not run user applications applications on end systems allows for rapid app development, propagation application transport network data link physical application transport network data link physical application transport network data link physical 5 Application Layer 2-6 Application architectures possible structure of applications: client-server peer-to-peer (P2P) 6 Application Layer 2-7 Client-server architecture server: always-on host permanent IP address data centers for scaling clients: communicate with server may be intermittently connected may have dynamic IP addresses do not communicate directly with each other client/server 7 Application Layer 2-8 P2P architecture no always-on server arbitrary end systems directly communicate peers request service from other peers, provide service in return to other peers self scalability – new peers bring new service capacity, as well as new service demands peers are intermittently connected and change IP addresses complex management peer-peer 8 Application Layer 2-9 Processes communicating process: program running within a host within same host, two processes communicate using inter-process communication (defined by OS) processes in different hosts communicate by exchanging messages client process: process that initiates communication server process: process that waits to be contacted aside: applications with P2P architectures have client processes & server processes clients, servers 9 Application Layer 2-10 Sockets process sends/receives messages to/from its socket socket analogous to door sending process shoves message out door sending process relies on transport infrastructure on other side of door to deliver message to socket at receiving process Internet controlled by OS controlled by app developer transport application physical link network process transport application physical link network process socket 10 Application Layer 2-11 Addressing processes to receive messages, process must have identifier host device has unique 32-bit IP address Q: does IP address of host on which process runs suffice for identifying the process? identifier includes both IP address and port numbers associated with process on host. example port numbers: HTTP server: 80 mail server: 25 to send HTTP message to gaia.cs.umass.edu web server: IP address: 128.119.245.12 port number: 80 more shortly… A: no, many processes can be running on same host 11 Application Layer 2-12 App-layer protocol defines types of messages exchanged, e.g., request, response message syntax: what fields in messages & how fields are delineated message semantics meaning of information in fields rules for when and how processes send & respond to messages open protocols: defined in RFCs allows for interoperability e.g., HTTP, SMTP proprietary protocols: e.g., Skype 12 Application Layer 2-13 What transport service does an app need? data integrity some apps (e.g., file transfer, web transactions) require 100% reliable data transfer other apps (e.g., audio) can tolerate some loss timing some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” throughput some apps (e.g., multimedia) require minimum amount of throughput to be “effective” other apps (“elastic apps”) make use of whatever throughput they get security encryption, data integrity, … 13 Application Layer 2-14 Transport service requirements: common apps application file transfer e-mail Web documents real-time audio/video stored audio/video interactive games text messaging data loss no loss no loss no loss loss-tolerant loss-tolerant loss-tolerant no loss throughput elastic elastic elastic audio: 5kbps-1Mbps video:10kbps-5Mbps same as above few kbps up elastic time sensitive no no no yes, 100’s msec yes, few secs yes, 100’s msec yes and no 14 Application Layer 2-15 Internet transport protocols services TCP service: reliable transport between sending and receiving process flow control: sender won’t overwhelm receiver congestion control: throttle sender when network overloaded does not provide: timing, minimum throughput guarantee, security connection-oriented: setup required between client and server processes UDP service: unreliable data transfer between sending and receiving process does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup, Q: why bother? Why is there a UDP? 15 Application Layer 2-16 Internet apps: application, transport protocols application e-mail remote terminal access Web file transfer streaming multimedia Internet telephony application layer protocol SMTP [RFC 2821] Telnet [RFC 854] HTTP [RFC 2616] FTP [RFC 959] HTTP (e.g., YouTube), RTP [RFC 1889] SIP, RTP, proprietary (e.g., Skype) underlying transport protocol TCP TCP TCP TCP TCP or UDP TCP or UDP 16 Securing TCP TCP & UDP no encryption cleartext passwds sent into socket traverse Internet in cleartext SSL provides encrypted TCP connection data integrity end-point authentication SSL is at app layer apps use SSL libraries, that “talk” to TCP SSL socket API cleartext passwords sent into socket traverse Internet encrypted see Chapter 8 Application Layer 2-17 Application Layer 2-18 Chapter 2: outline 2.1 principles of network applications 2.2 Web and HTTP 2.3 electronic mail SMTP, POP3, IMAP 2.4 DNS 2.5 P2P applications 2.6 video streaming and content distribution networks 2.7 socket programming with UDP and TCP 18 Application Layer 2-19 Web and HTTP First, a review… web page consists of objects object can be HTML file, JPEG image, Java applet, audio file,… web page consists of base HTML-file which includes several referenced objects each object is addressable by a URL, e.g., www.someschool.edu/someDept/pic.gif host name path name 19 Application Layer 2-20 HTTP overview HTTP: hypertext transfer protocol Web’s application layer protocol client/server model client: browser that requests, receives, (using HTTP protocol) and “displays” Web objects server: Web server sends (using HTTP protocol) objects in response to requests PC running Firefox browser server running Apache Web server iPhone running Safari browser HTTP request HTTP response HTTP request HTTP response 20 Application Layer 2-21 HTTP overview (continued) uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is “stateless” server maintains no information about past client requests protocols that maintain “state” are complex! past history (state) must be maintained if server/client crashes, their views of “state” may be inconsistent, must be reconciled aside 21 Application Layer 2-22 HTTP connections non-persistent HTTP at most one object sent over TCP connection connection then closed downloading multiple objects required multiple connections persistent HTTP multiple objects can be sent over single TCP connection between client, server 22 Application Layer 2-23 Non-persistent HTTP suppose user enters URL: 1a. HTTP client initiates TCP connection to HTTP server (process) at www.someSchool.edu on port 80 2. HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object someDepartment/home.index 1b. HTTP server at host www.someSchool.edu