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waterskier2007's avatar

A question about ip adresses?

Asked by waterskier2007 (2050points) July 17th, 2008

so i really dont understand ip addresses? how do they work/how are they assigned. i know that ip addresses change. but how. and if im on my home network, then i leave and come back, is my ip address going to be the same as before?

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10 Answers

Skyrail's avatar

IP address ranges are allocated to ISP’s by companies like IANA who decide who gets what. So your ISP will be allocated a certain address range, say – (as a generic example). Your ISP will then have something like a large number of DHCP servers which your computer will ‘communicate’ with, you use the login details, your computer ‘talks’ to the ISP’s computers and then they assign an IP Address to you. If you’re ISP uses dynamic IP address’ it will just allocate you an IP address within it’s range that is currently free. If it’s fixed the ISP servers will just give you the same IP address everytime (see Dynamic and static IP addresses).

As for local networks it works on the same concept but they’re limited to the addresses allocated for private networks. For example, my router acts as a small DHCP server and so the computers on my home network will get the next free IP address available when the computers start up, or I can set which computers can have which IP by using a computer’s MAC address which is a unique ID to each ethernet enabled device.

I hope that’s clear/informative, if not don’t hesitate to ask for more information. I’m not an expert and I’ve no idea how the actual inner workings of an ISP works because I’ve never worked for one. But I know somewhere the ISP will be allocated an IP address range which will then allocate you one of these IP addresses for your usage.

Edit: oh, and domain names and IP addresses are a new subject altogether, which I do understand the basics of to :)

waterskier2007's avatar

so your house gets an ip address range from the ISP, but at that time the ISP doesnt know how many computers you will have on the network, so how does it know how many address to allocate for you in that range

Skyrail's avatar

Ah, how do you connect to the internet? Do you connect through a router with multiple computers on that single router?

waterskier2007's avatar

yes, one router to provide the wireless for 3 computers

Skyrail's avatar

Okay, your ISP will give your router a single IP address for accessing the internet/the outside world. Your router will allocate your 3 computers individual IP addresses within one of the three allowed private network ranges ( –, – or – these IP addresses are only accessibly locally. Even though you may access the internet with all 3 computers at the same time they each have the same IP address from the view of the internet as they are accessing it through your router, whereas they will have individual IP addresses on your router/local network. To understand more about how the router knows which PC to send the data to you have to go into packets, headers and other stuff I don’t quite understand, yet. :)

waterskier2007's avatar

oh i see. thanks a ton for the help and some awesome answers

Skyrail's avatar

It’s okay, anytime, well anytime I know what I’m talking about of course :)

JasonH's avatar

want the best ip setup go with a static ip if Accepted by ur isp

skorned's avatar

wow!! the above explanations are very long and comprehensive, I would read them if I wanted to reeally understand how IPs function. But the cliffs note version is:
Every network is free to assign its own IPs. So when your router gets switched on and connects to your ISP, they give you the first available free address on the internet, within the boundaries they are allowed. They usually have a whole block they can use, like 124.125.x.x, where they can assign you any 2 values for x.

Also, when your PC connects to your router, there is a separate local network formed, and the router can assign any IP it wants to your PC, without affecting operations, any website you visit will still see a request from 124.125.x.x. So your router will give you any free IP address that any other PC on your local network hasnt already been assigned, for example,

It’s almost as if every time you switched on your cell phone, you would get the first available number. Although, IPs can be set to be fixed, like telephone numbers, but if the settings conflict and two devices on the same network, like two PCs on the same laptop, are set by mistake to have the same IP, the network won’t function right.

OK never mind, my answer ended up being just as long :S

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