IP - HTTP
IP address - domain name :
> host www.math.utk.edu returns:
www.math.utk.edu is an alias for noether.math.utk.edu
noether.math.utk.edu has address 126.96.36.199
Reverse lookup: > host 188.8.131.52 returns: 184.108.40.206.in-addr.arpa domain name pointer noether.math.utk.edu
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
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 220.127.116.11:80
HTTP protocol :
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".
which must have file permissions: drwx r-x r-x
and files in it must have permissions: -rw- r-- r--
else contents will be displayed (and can be downloaded! , even if owner did not mean it...)