UTK - Math 171 - Alexiades

            IP - HTTP

IP address - domain name :

  • Each device connecting to a network must have unique IP address, in 4 octets:
      > host www.math.utk.edu   returns:
        www.math.utk.edu is an alias for noether.math.utk.edu
        noether.math.utk.edu has address 160.36.108.56
      Reverse lookup: > host 160.36.108.56 returns: 56.108.36.160.in-addr.arpa domain name pointer noether.math.utk.edu
  • The IP name has 3 parts:
        1. host name: 56 = noether (local server)
        2. domain name: math.utk (36 = utk is class B, 108 = math" Class C)
        3. top level domain (class A): 160 = edu
  • DNS (Domain Name Server) translates IP name to IP address
      request is first sent to top level domain: 160=edu
      DNS in top domain looks up "utk" finds 36 and send request to it
      DNS in "utk" looks up "math" finds 108 and send request to it
      DNS in local "math" server looks up "noether" finds 56 and sends request to it, which responds.

    Connection Ports :
      Servers listen to specific "ports" (unix 'sockets') for request for service, one for each service they provide.
      WWW service at port 80, FTP at 21, login at 23, email (smtp) at 25, etc
      So actually a Web request to math server goes to 160.36.108.56:80

    HTTP protocol :
  • Based on client-server technology. Client is the browser, server is the web-server.
  • URL (Uniform Resource Locator):   http://www.math.utk.edu/~vasili/171/
  • a "link" on a webpage is a GET request for a specific file on a WWW server, specified by a URL
  • Entering or clicking on the URL on a Web browser:
        http://www.math.utk.edu/~vasili/171/   sends a GET request
        to the math webserver port 80, asking for the file "~vasili/171/".
      "~vasili" is a user's name on it (my login name on it),   and "171/" actually means "171/index.html" by default.
      I manage all files in my home dir "/home/dept/vasili/", and web docs must be in the dir "/home/dept/vasili/www-home/".
      So actually, "~vasili/171/" means file 171/ in web-docs dir of home dir of user "~vasili".
  • HTTP is configured to have access ONLY to the web-docs directory: ~username/www-home/
      which must have file permissions:   drwx r-x r-x
      and files in it must have permissions:  -rw- r-- r--
  • Each sub-dir in docs-dir should contain a file "index.html" ("default.html" on some servers),
      else contents will be displayed (and can be downloaded! , even if owner did not mean it...)
  • If you know the full path to a file then you can view it on a browser.