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Notes 1
Searching the Web
 | Boolean expressions are used to do Web searches with increased precision.
 | Boolean: True or False |
| ( Ian AND Allen ) OR ( Ian AND FreeNet ) |
| The precise syntax used depends on the search engine; read the help page! |
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Understanding a URL
URL syntax for a Network (Internet-style) item:
protocol://computer_address_or_name/pathname
Examples of common protocols:
http://idallen.com/teaching/
http://idallen.com/
ftp://netsrv.algonquincollege.com/
telnet://telnet.ncf.carleton.ca
news://news.idallen.com/algonquinc.cst.fasttrack-98.announce
Components of a Universal Resource Locator (URL):
| http: HyperText Transfer Protocol (standard Web pages) |
| ftp: File Transfer Protocol (for downloading/uploading files) |
| telnet: for direct terminal-to-terminal connections to remote computers |
| gopher: a predecessor of http, largely replaced by http |
| news: Network News Transfer Protocol (NNTP) for Usenet-style discussion
groups |
| mailto: Simple Mail Transfer Protocol (SMTP) for sending E-Mail |
Note that the host name part of a URL is not case-sensitive.
Understanding an Internet E-Mail address
Syntax for an Internet email address:
user_id@computer_address_or_name
Examples of email addresses:
idallen@freenet.carleton.ca
aa610@FREENET.CARLETON.CA
Note that the host name part of a mail address is not case-sensitive.
Computer Addresses and Names
Much of the connecting done between machines on the Internet happens between computers
labelled by numbers, not names. These numbers are called "IP" (Internet
Protocol) numbers. To establish a connection between the machines, the friendly,
human-readable names must be turned into numbers. Tables of these name-to-number maps
typically reside on computers that serve as Domain Name Servers (DNS).
| Computer names are hierarchical, separated by periods, with the most specific components
on the left and the most general, large domains on the right, e.g.
"news.idallen.com". There is no fixed limit to the depth of the
hierarchy; however, more than four levels is uncommon.
| There are a fixed number of "top level" domains, e.g. .gov, .edu, .com, .ca,
.hu, .jp, .us, etc. |
| Each domain gets control of the naming scheme used inside it and can use any naming
convention it likes, e.g. .com.au, .edu.au, .net.au, etc. |
| Name servers only need to know how to find the name servers of the next level in the
name tree - no server needs to know the whole tree. |
|
| IP numbers are also hierarchical; however, the most specific parts of the IP number are
on the right, and the most general, large network components are on the left, e.g.
"134.117.136.20". The IP numbers written this way are often called in
"dotted quad" form. Two machines on the same network may have numbers such
as 134.117.136.20 and 134.117.136.24. |
| Name servers "cache" name requests for a period of time (the "time to
live"). Subsequent requests for the same name are served from the cache until
the entry expires, then a fresh request is made to update the cache. |
Unix commands
Most Unix commands that handle machine names will accept either the name of a computer
or its IP address in dotted-quad form.
| ping: sends a request for an "echo" to the remote machine;
shows how long it took |
| traceroute: traces the network route taken by a connection between this
machine and a remote machine; shows the route and the time taken to get to each machine
along the route |
| host: for a particular host, displays information about the IP
addresses and MX (mail exchange) records stored in the DNS for that host |
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