Posted by Vince on 11/3/2009, 6:40 pm, in reply to "Re: Firewalls"
68.144.14.16
A router is a sorting machine, much like a sorting machine in a post office.
A postal letter will have a zip code -equivalent to the first part of an IP address- which tells postal workers WHERE to send the letter TO ....... generally. The zip code tells postal workers to direct the letter to a specific city or region. Once the letter arrives at the city or region, it must then be sorted further to direct it to specific letter carriers on specific routes. The letter carrier then does the final sorting by checking the address on the letter and putting it into the correct address postal box on the outside of houses.
Computer network communication works much like the postal service. Data is sent in packets and every packet has a destination address and a return address written on it. So you can think of packets as individually addressed envelopes with data contained inside of the envelopes, traveling to and fro between source and destination addresses.
In the olden daze of internet, IP providers used to sell their customers single IP addresses for each single computer in each household. Thus, if a household had 4 people who EACH wanted to have access to the internet, they would have to buy 4 separate IP addresses from the IP provider, with the provider laughing all the way to the bank. It isn't at all necessary to have separate IP addresses for numerous people at a single location because the data is all streaming up and down the same wires anyway.
Well then, as the internet "exploded" in usage, IP addresses started to become scarce. There are only about 4 billion addresses available on the most commonly used 32 bit internet protocol -IPv4- and it was beginning to cost IP providers a HUGE amount of money to reserve extra addresses ......... for which they had no hope of selling any more at such inflated prices. In essence, they were forced to make do with what they got. So they dropped that single-IP-for-each-single-computer option like a hot potato.
Meanwhile, "someone" came up with the idea of using routers in home environments for achieving essentially the same thing that commercial routers were doing on the internet! That is .......... why NOT have households use ONE internet address to supply numerous people in single households with numerous separate, unique and distinct connections? And thus was the practice of home routing established.
Using a home router system, EVERYONE in the household shares the same IP address. However, their own individual activities have to be sorted and then notated in order to keep them all separate. This isn't really all that hard to do.
The router interfaces with the modem and the modem only responds as one single IP. Therefore, the router has to design its own method of noting and sorting traffic to individual computers behind itself. It does this by creating a "routing table."
The router may be communicating with 4 different computers behind itself, with 4 separate LOCAL IP addresses ....... like .........
A) 192.168.1.5
B) 192.168.1.6
C) 192.168.1.7
D) 192.168.1.8
...but it never presents these to the outside world.
Instead, it receives data from computer A, addressed to Google.com...
Destination address = 209.85.135.104 = Google.com
Return address = 192.168.1.5
It strips off the 192.168.1.5 from the return address on the packets which this computer is sending to Google and replaces it with its own routing table's equivalent symbol ...... say A. It then writes the return address on the packet as .... the main IP address, followed by the A notation.
Google responds to the main IP address with notation attached ......the router receives it and says, "oh, A belongs to 192.168.1.5" ........ and strips off the entire destination address, replacing it with 192.168.1.5 ......... and then sends it out into the backside, the local area network side, the home side ......... where that A computer then reads the address to itself and picks up its own packets like you would pick up mail from your mailbox.
This method allows 4 different computers in a household to connect with 4 cables to the one router and ALL be able to use the internet independently!
The beauty of the home router is that it doesn't allow the IP provider to charge extra for every computer attached ....... and ........ it provides a natural firewall to the outside world.
If some nefarious hacker is sitting out there in the world wide web, looking for machines to hack into, he can well attempt to hack into your IP address ...... but ....... the router gets his hack messages and says, "ok, so WHERE do you want your stuff to GO to?" The hacker (or worm) has absolutely no idea how the router is notating behind itself and is therefore unable to go anywhere or do anything further.
-Vince
Message Thread:
« Back to thread
