Digital Literacy - Basic Technical Concepts (Session 1)

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Basic Digital Literacy, including Internet connectivity, DNS, Email, HTTP Process, and Troubleshooting.


  • 1. Digital Literacy Series Digital Literacy Session 1 - Basic Technical Concepts Prepared by Bill Condo

2. Digital Literacy Series What Were Covering How the Internet is connected and by who How the Domain Name System (DNS) works How email is transmitted and stored How web servers and browsers work How to troubleshoot internet issues Technical FoundationalTopics This is the rst session of a multipart series that will help ll in any deciencies around the Internet and digital technologies. ! In this rst session, well start with the foundational elements that enable the Internet to work, and tips and tools to troubleshoot when things arent working as expected. ! ! ! Series Introduction 3. Digital Literacy Series The Internet The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (TCP/IP) to link several billion devices worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless, and optical networking technologies. 1 The Internet (internetworking) dates back in part to ARPANET and other networks, and is commonly attributed in part to Vint Cerf. 1) 4. Digital Literacy Series The Internet The total count of Internet users continues to grow exponentially. The number of devices are growing even faster, as many people have multiple devices connected. 1) 0 750 1500 2250 3000 1990 1995 2000 2005 2010 2013 Internet Users in Millions 1 2.7 b 44 m 5. Digital Literacy Series The Internet Tier 1 ISP Tier 1 ISP Tier 2 ISP Tier 2 ISP Tier 2 ISP Tier 3 ISP Tier 3 ISP Tier 3 ISP Tier 3 ISP Customers (Business and Consumers) P P 3 Tiers of ISPs connect the Internet, with Tier 1 being the largest, core companies. P Peering points connect major ISPs to one another and are what enable the Internet to work. P 6. Digital Literacy Series The InternetTIER1TIER2TIER3 Local and Regional ISPs 7. Digital Literacy Series The Internet The Internet is not the same as the World Wide Web, but instead enables it. The HTTP and HTTPS protocols (Web Browsing) run on top of the Internet, just as SMTP and IMAP (Email), and FTP (File Transfer Protocol). WWW Email FTP 8. Digital Literacy Series Domain Name System DNS usage is typically transparent to the end-user, tied internally to web browsing, email, and other Internet services. DNS operates on what are called zones, which consists of a top level domain name, such as The zone le usually contains multiple records, some of which are address resolution (a, cname records), mail pointers (mx), and text records (txt). DNS records are normally cached after a request by a users computer, and by third-party DNS servers. 9. Digital Literacy Series Domain Name System 1 2 3The local computer references a domain name and a DNS lookup request is created. Your request is sent to the server as congured from your computer, and then may be sent upstream to other servers until the server responsible for the domain provides the authoritative answer. Your ISPs Local DNS Server Another ISP DNS Server Domains DNS Server Response 1 4 5 6 2 3 The result is then sent back through the original path and provided to the computer. 4 The resulting IP address is then used to make the nal request (website, email, etc.) [5,6]. 10. Digital Literacy Series Email Behind web browsing, email is second most common use of the web. Desktop email clients remain behind the standards of web browsers, and a large number of people use web mail (ie Gmail). Email works a lot like the post ofce, working in a hub and spoke manner. Email messages themselves are most like postcards, in that anyone along the route can read the full message. 11. Digital Literacy Series Email 1 3The sender drafts the email and authenticates with their outgoing (SMTP) mail server. The message passes through one or more third-party mail servers until a connection can be made to the nal server. Senders Mail Server Mail Server Mail Server Recipients Mail Server Recipients AccountSenders Account 1 2 3 4 5 2 The senders server accepts the message for delivery and passes it to another mail server, closer to the the recipients server. 4 The nal mail server checks for the addressed account and stores it locally if the user exists, otherwise sending an error message back. 5 The recipient will be notied/ receive the message on their next connection to their mail server. 12. Digital Literacy Series Web Servers Web server software is built to process a web request, compile the data, and deliver a response. Web servers can process simple requests, such as those for an image or style sheet, or more complex ones, such as pages with back-end programming and resource intensive database connections. Web servers typically handle multiple requests from a single user concurrently, letting a browser load multiple assets at the same time. 13. Digital Literacy Series Web Servers The most popular web server is from the Apache Foundation. Apache HTTP Server and Nginx (Engine X), both open source projects, account for over 66% of all active web servers. 0 15 30 45 60 4/10 4/11 4/12 4/13 4/14 Microsoft IIS Other Nginx Apache 52% 1) Active Web Servers % 1 14% 14. Digital Literacy Series Web Process 1 3Browser Requests URL Web ServerClient Computer 1 2 Request is routed to the correct web server 5 6 Request is received and any back-end logic is processed Response is routed back to the clients browser Response is loaded into the browser and any external items (i.e. images) are requested 6 3 4 2 5 4 Response is formatted and sent 15. Digital Literacy Series Web Browsers Web Browsers render websites, locally run javascript, interpret style sheets, and store session and local data. Browsers build on top of this core functionality with bookmarks, history, extension support, and UI components. Each browser has its own rendering engine, script interpreter, and API layer. Its up to each browser to implement their components against the latest HTML, Javascript, and CSS standards, which some have historically done better than others. 16. Digital Literacy Series Web Browsers 17.5% 35% 52.5% 70% 2009 2011 2013 2014 Internet Explorer Default browser for Windows thats continuing to lose marketshare each year Safari Default browser for OSX thats beneted from the increased popularity of Macs Chrome Introduced in 2008, it has become the most popular browser, it renders quickly, and has a vibrant third-party extension ecosystem Firefox From the roots of early browsers Mosaic and Netscape, Firefox was previously the most popular browser and continues to be a common choice 1) Browser Market Share % 1 Other Notable Browsers Opera / Opera Mini Opera has a small following on the desktop and is installed on some phones Android Browser Shares some features of Chrome 17. Digital Literacy Series Troubleshooting ! When troubleshooting an issue, its important to be able to isolate the cause to one of three areas: user, network, or server. Using a series of questions, we can determine what path we should explore with additional effort. User/Computer Level Network/Internet Level Datacenter/Server Level If the problem(s) are within a local computer or local network. If the problem(s) are within a local ISP, or backbone provider. If the problem(s) are within the nal datacenter or within the web server. 18. Digital Literacy Series Troubleshooting Do you have trouble access all websites (or other services)? Do you have trouble sending all email? Do you get an authentication error message? User/Computer Level 19. Digital Literacy Series Troubleshooting Do only a certain group of websites (or services) not function, while others work successfully? Has your ISP communicated an outage? Is only one type of service (web, email, ftp, chat) unavailable, while others are functional? Network/Internet Level 20. Digital Literacy Series Troubleshooting Has a service published a report of an outage (i.e. Gmail)? Have you isolated the trouble to only one single website (or service)? Do you get a specic service error message indicating a connectivity, functional, or over capacity message for this resource? Datacenter/Server Level 21. Digital Literacy Series Troubleshooting Mac OSX has a group of network tools available inside of the Network Utility app. This provides an easier interface compared to using some of the items on the command line. Windows also has some of the tools via the command line. Built-inTools for OSX 22. Digital Literacy Series Troubleshooting A number of tools exist which test the availability of websites from third party locations. This will help you understand where a problem might be located. Down For Everyone? 23. Digital Literacy Series Troubleshooting Ping is a tool that tests connectivity to a host by passing a small data packet to the machine and verifying that the response is received. Note: ping is not 100% accurate because some hosts block this communication. Ping 24. Digital Literacy Series Troubleshooting Trace route is a tool that will display each step (host) that was used along the way in order to access a specied host. This data can be combined with address IP info to track the geographic path taken. Trace Route 25. Digital Literacy Series Troubleshooting Whois is the look up tool for domain registration, which gives you the registration dates, company, and DNS server settings. Some whois data may be set as private, hiding the company that registered a domain. Domain Whois 26. Digital Literacy Series Troubleshooting Whois data may only be available directly from the domain service that the TLD (Top Level Domain) is registered through. In this example, we need to visit to get a full whois record. Domain Whois 27. Digital Literacy Series Troubleshooting DNS records may be looked easily up with number of web- based tools. Verify a new IP address setting or debug existing settings. Website records typically use whats called A records, but may also use CNAME records as well. DNS Record Lookup 28. Digital Literacy Series Troubleshooting With this result, we can see the domain is pointed to the IP Address of The TTL, or time-to-live is set for one hour. This in an instruction to cache (or remember) the result for that long. DNS Record Lookup 29. Digital Literacy Series Troubleshooting If youre not sure where a site is hosted (Squarespace, Godaddy, etc), or want to see what type of web server a site is running, you can look it up with this tool from Netcraft. Because most servers return this info with a request, it can be captured and documented. Web Server Information 30. Digital Literacy Series Troubleshooting In this example we can see the web host is Godaddy, the server is running the Linux operating system, and using the Apache web server. In some cases youll see a longer, historical list. Web Server Information 31. Digital Literacy Series Additional Resources Internet DNS Email 32. Digital Literacy Series Additional Resources Web Servers Web Browsers Troubleshooting 33. Digital Literacy Series What did you do to get better today?