Material on this page © TK Boyd July 2017... but if you want to translate the page, or circulate it on DVD or intranet, I will allow that with some conditions.
This is one page of many in a sequenced series that try to get you connecting things to LANs and the internet with as few tears of frustration as possible. There is an overview page, which is your table of contents to this material.
To start things off we will look in a little detail at the "magic" behind something millions of people do, every day, without a second thought...
If you are reading this directly from the internet, you are doing it now.
You have some sort of "computer", be it a laptop, desktop, tablet, smartphone (or other!) "connected to the internet", and you are reading this text.
(Just to bring this "out" of the virtual world, place it in the "real" world, just for a change, I will tell you that this text started life, when I poked the buttons on a Logitech Bluetooth keyboard, which passed my wants on to a simple Samsung Android tablet in a modest hotel basement room in west London, 30 June 2017, when I had a little time on my hands before going to an end- of- year show put on by the Royal Ballet School, featuring the kids in their junior department. (White Lodge.) (End of digression!))
I'll speak of "your computer" for the rest of this essay... it really doesn't matter if you are using, say, a smartphone. It doesn't matter to the issues I am going to discuss in these pages. Nor does it matter what operating system you are using. (E.g. Windows, Linux, other)
Your computer will... in any sensible, "ordinary" circumstance... be connected to a LAN, a "local area network"... although you may not be aware of this.
Even if your computer is the only device on that LAN at the moment, the LAN will be capable of connecting to multiple devices. It will have a "switch", and/ or "router" on it somewhere, to manage the paths messages take, in traveling across the LAN. (Switches and routers are not exactly the same thing, but for now we'll ignore the differences. you probably have one of each!)
And your LAN will have a modem attached to it. (That device may share one physical box with the switch/ router.) The modem will connect to "the internet" on one "side", and, through the switch/ router to the LAN on the other. The switch/ router manages the passing of messages back and forth, between your LAN and the WAN (internet). (The modem "just" converts the messages coming "out" of the switch/ router to messages suitable for the WAN's needs.)
HERE'S an IMPORTANT CONCEPT: The switch/ router WILL have two "addresses". It will have one address on the LAN side.... quite possibly 18.104.22.168 (but not necessarily), and a DIFFERENT address as far as "the internet" , aka WAN, is concerned.
LAN and WAN addresses consist of 4 numbers (sometimes 6, in the case of the WAN), separated by full stops.
The numbers are always in the range 0-255 (inclusive)(This is because 0-255 can be shown by eight 1s and zeros. 255 is sort of a "binary 9999".
("IMPORTANT CONCEPT" mostly covered.)
(Slight digression: These numbers are also sometimes written in HEX. I can show the number of days in the week as "7" or "seven" or "xxxxxxx", or "sept" ("sept" is seven "written in" French. Not my term "written in"... I'm going to use it again in a moment.).
The decimal ("ordinary") numbers 0-255 can be shown by 0-$FF. The "$" says :"this is a number written in hex. When you have a number written in hex, the digits can be 0,1,2...7,8,9. And A, B, C, D, E or F are also okay, as part of a hex number. (By the way, "D" is as good as "d" when you are writing numbers in hex. I.e. the "case" of the letter is not significant. If the number is, say, $4D, that's the same as $4d. (In our usual system of writing numbers, "decimal", $4d would be 77, if you were wondering. Not important, now, to be able to convert.))
When something on the WAN wants to "talk with" your modem, it will use the modem's WAN address. When something on the LAN wants to talk to the switch/ router (and though them to the modem, to get to the internet (WAN)), it will use the LAN address.
Nothing on the LAN side can talk DIRECTLY to anything on the WAN. Nothing on the WAN side can talk DIRECTLY to anything on the LAN side. (But there are ways to send stuff (messages) to the modem, from either "side". That stuff (message) will be formed in a way that says "please pass across to the other thing (LAN of WAN) you are connected to".)
Whew! Take a breath! Quickly re-scan the above, if it wasn't already old, old news to you. We're about to go on, and use some of the above to consider the next level of complexity
Let's say you found the page you are reading by going to Google and doing a search on "help me with how hex numbers are shown".
What BROWSER do you use? I use Firefox. (That was just to reassure you about what I mean by "browser".)
To "search with Google", you need to put "help me with how hex numbers are shown" into a browser.
It creates a "thing" which goes across your LAN to your switch/ router/ modem. The modem sends it off... to the right place (no small feat!)... out on the internet (one of Google's SERVERS). The "thing" sent off from your modem carries a "return address", by the way. Google's server puts together an answer to your query, and, using the return address, sends it back to your modem. Your modem sends it to your switch/ router, and THAT sends it off across your LAN to your computer, and, presto, the link suggestions (The answer to your Google search for "help me with how hex numbers are shown") are there in front of you!
(Yes, to those who know... I've left out some details. Be patient.)
Why have a made a fuss about...
"computer to switch-router-modem"...
... "switch-router-modem to Google server"?
Because if you are reading this essay, you probably want to have more than one thing on your LAN, and so I need to go into the following detail...
Suppose there are TWO (simple) computers on your LAN? And that both are in use at the same time. We'll say that you are Alice, and that Bob is across the room using same LAN and switch/ router/ modem that you are using. And he, too, is fetching information from the web.... but DIFFERENT information.
That may be both simpler and more complicated than you think.
Here are the critical details....
When you, Alice, sent your request for some links about "connect PC to internet", the messages flowed as already described. And when Bob sent his search request to see whether or not a man is still wrong if he speaks when there is no woman is within 200 miles, the messages in connection with that also flow as already descibed. Mostly. At very nearly the same time.
But think about it. There' something WEIRD going on: When those requests for answers left your modem, and went off across the internet, the return address, as far as the server the requests went to was concerned, only specified your modem!
And so, the answer is sent back "to" "the modem". The clever bit happens in the switch/ router/ modem. It knows where, on the LAN, to pass that answers to. Whew!
We will be going into more detail about how this magic happens in subsequent pages.
The search engine is not intelligent. It merely seeks the words you specify. It will not do anything sensible with "What does the 'could not compile' error mean?" It will just return references to pages with "what", "does", "could", "not".... etc. It searches only my SheepdogGuides.com pages.
I also offer an alternative search engine (looking only at pages from all of my sites) use the Google Custom search box at the page the link takes you to.
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