OSI Model. Hybrid Model. Software outside the operating system Software inside the operating system. Only Internet addresses used

Transcription

1 Chapter 8 What happens at the Application Layer? Domain Name System (DNS) Electronic Mail World Wide Web Hypertext Transfer Protocol (http) Internet Application - Multimedia Content Delivery

2 OSI Model Hybrid Model Software outside the operating system Software inside the operating system Only Internet addresses used Physical addresses used

3 The Domain Name System (DNS) is a directory lookup service that provides a mapping between the name of a host on the Internet and its numerical address. DNS makes use of a distributed, hierarchical database to maintain a mapping from names to addresses and to provide related information about hosts on the Internet. RFCs 1034 and 1035

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5 root level Top level domain generic dot (the root of the Internet namespace) countries TLD name servers authoritative name servers zones

6 root level Top level domain generic dot (the root of the Internet namespace) countries TLD name servers authoritative name servers Cybersquatting register a domain name for cheap to sell it later to an interested party for more profit. Register a domain with a registrar appointed by ICANN (Internet Corporation for Assigned Names and Numbers), e.g., registrar for.com Tuvalu country ( inhabitants on an archipelago in Pacific) sold their assigned country domain.tv with 50 mil $. As for comparison, their GDP in 2013 was 38 mil $.

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8 What is the IP for No idea Let me ask a resolving name server browser Operating System

9 Oh, here it is nytimes.com name server No idea Let me ask a resolving name server What is the IP for TLD name server No idea but I know where nytimes.com is ask there.. Operating System No idea but I know where.com is ask there.. Root name server Local resolving name server No idea but I know where the root is

10 Domain name space: DNS uses a tree-structured name space to identify resources on the Internet. DNS database: Conceptually, each node and leaf in the name space tree structure names a set of information (e.g., IP address, type of resource) that is contained in a resource record (RR). The collection of all RRs is organized into a distributed database. Name servers: These are server programs that hold information about a portion of the domain name tree structure and the associated RRs. Resolvers: These are programs that extract information from name servers in response to client requests. A typical client request is for an IP address corresponding to a given domain name.

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12 Domain Names.com.net.edu.org.de Google skyscanner cornell Ford jacobs-university Host Names NevPC trsys Any PC/workstation, printer, server, router on the network. Identified by a host name and an IP address (check with ipconfig /all on Windows, ifconfig on Linux). Hosts.txt (Windows users) Edit (as administrator) C:\Windows\System32\drivers\etc\hosts.txt Add a new line with Try to access with Firefox/Chrome/other browsers Hosts.txt (Linux users) # sudo gedit /etc/hosts

13 Every domain, whether single host or top level domain, can have a set of resource records (RR) associated with it. The domain to which this record applies. How stable the record is.

14 alias translation

15 One cannot distinguish the names of subdomains from the names of individual objects or the type of an object using only the domain name syntax.

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17 Why do people use them? Are they legal? ETHICS!!!

18 Pay fee or I drop your packets brutuspc I shall not pay 8E/h! only DNS traffic allowed redserver.com Airport / hotel / public hotspot

19 How can a network administrator detect the breach? Pay fee or I drop your packets runs iodine client script brutuspc I shall not pay 8E/h! redserver.com Airport / hotel / public hotspot runs iodine server script (preconfigured by Brutus)

20 What you should know when registering a domain (e.g., yourname.com)? Domain Name Registrars (GoDaddy.com, NameCheap.com, enom.com, justhost.com: go to any of them and check if yourname.com is available, pay the fee and look for a webhosting plan) Web hosting (get a hosting plan and obtain from them the names of their primary and secondary nameservers) link your domain to your web host's name servers (go to your domain name registrar and enter the primary and secondary nameservers addresses information, e.g. ns1.webhosting.com, ns2.webhosting.com) you can now proceed to making your website/uploading on the web hosting servers

21 Architecture and Services The User Agent Message Formats Message Transfer Final Delivery Basic functions Composition Transfer Reporting Displaying Disposition

22 Envelopes and messages. (a) Paper mail. (b) Electronic mail.

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24 RFC 822 header fields related to message transport.

25 Some fields used in the RFC 822 message header.

26 Problems with international languages: Languages with accents (French, German). Languages in non-latin alphabets (Hebrew, Russian). Languages without alphabets (Chinese, Japanese). Messages not containing text at all (audio or images).

27 RFC 822 headers added by MIME.

28 The MIME types and subtypes defined in RFC 2045.

29 A multipart message containing enriched and audio alternatives.

30 Transferring a message from elinore@abc.com to carolyn@xyz.com.

31 (a) Sending and reading mail when the receiver has a permanent Internet connection and the user agent runs on the same machine as the message transfer agent. (b) Reading when the receiver has a dial-up connection to an ISP.

32 Using POP3 to fetch three messages.

33 A comparison of POP3 and IMAP.