How ISPs work

Hi there

I am not much into networking but I do have an idea how a simple network work but still have few vague concepts will be great if someone can help me with.

Now with the ISP, the provide home and businesses with Internet access.

For businesses they provide them with public ip addresses to use it as they please, web-servers, e-mails etc.

For homes? When someone gow to www.whatismyip.com he is presented with the IP address of his ISP default gateway right?

But, how do the ISP provide internet access to homes? do home share on public IP_ address according to areas for example? I have a LAN at home and some one else might have a LAN in the same IP scope if we share the same IP router for the same provider why not connect together? No routing?

  A brief description of the structure would be great the whole concept is vague in my mind.

Thanks
M SOSAsked:
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Peter HutchisonSenior Network Systems SpecialistCommented:
BT now allows ISPs to share their PSTNs (Public Switched telephone network) to connect users to the internet via existing digital telephone lines.  This uses ADSL (Asynchonrous Digital Subscriber Line) technology
ISPs will have their own network instrastructure to take the data from the ADSL links into its IP insfrastructure with its own routers, DNS servers, DHCP servers and web and mail servers available to its customers.
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JohnBusiness Consultant (Owner)Commented:
The ISP (Internet Service Provider) provides you with Internet, One or more IP addresses, and a Modem.

It is best (not outright simplest) to put a good router in front of the modem to form your network. You can set up whatever LAN scope you wish. The router can be a wireless router with wired ports for desktop computers. This will work well.

Your modem may need to be put in Bridged mode for this to work.

However, when you put it together as suggested, you have a nice, flexible home or small office network.  

I use this myself and for clients.
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Fred MarshallPrincipalCommented:
The internet service provider assigns a public IP address to your interface device.  It may be on a modem or a modem/router or via a modem in bridge mode onto a router or even a single computer .. but it's at your location.
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Dave BaldwinFixer of ProblemsCommented:
Your local network uses 'private non-routeable' IP addresses.  You connect to your ISP thru a DSL or cable modem (or dial up connection).  The IP address that your ISP uses to connect to you is part of a bank of IP addresses that the ISP has applied for and had assigned to them thru ICANN.  

There used to be an "Internet Backbone" but there isn't anymore.  Instead, ISPs connect to each other and often do so thru internet networking companies that have installed and built up national and international networks which are mostly over fiber.  The fiber connections have been installed by large companies and telephone companies and the big cable companies.

Here's an article on 'internet maps' by the guy who invented the internet,  Timothy B. Lee: http://www.vox.com/a/internet-maps
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Faruk Onder YerliOwnerCommented:
Your first question answer is No.  You may never see your gateway IP in WhatismyIP side. You will always see assigned IP by ISP.

Your second question answer is NAT . Network Address Translation. Private IP is translating to Public IP with this technology. All routers are supporting NAT that you may communicate with all world.
 
you can find below link how it works.
http://computer.howstuffworks.com/nat.htm
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M SOSAuthor Commented:
OK Thanks guys

Just one more question Pls

When I browse to www.whatismyip.com and get my public IP address......does that belongs only to me or there are many other places this IP is shared.

Thanks
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Faruk Onder YerliOwnerCommented:
It depend on ISP rules.
- It can be temporarily your usage,
- it can be static IP which is assigned you by ISP
- it can be shared with other customer over NAT.

According to ISP IP pool size and service location one of 3 scenario can be used.
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JohnBusiness Consultant (Owner)Commented:
get my public IP address......does that belongs only to me <-- As noted in the prior post, it depends.

As long as you have it, it is yours - no one else can use it.

Now the ISP can change it (nature of dynamic IP addresses), but governments are interested in tracking you, so ISP's are not changing IP addresses as much any more.

Where I am, I do not see IP addresses shared and so you can be reasonably confident that only you has that IP address.
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