How does ISP trace an IP address if it can be changed constantly?

I am able to change my IP address whenever i want using mac address through my router.



xx.xxx.##.###



(x doesn't change but # changes)



I was wondering if people are allowed to do this, how would an ISP be able to track which user was using which IP? I'm sure there is more than one person with xx.xxx)How does ISP trace an IP address if it can be changed constantly?
They don't.



Your ISP doesn't know or care what the internal addresses of your devices are. It's of no consequence to them or anybody else. So you can change your internal addresses all you want and your ISP won't know.



But as for how they trace which customers had which IP addresses during which time periods, it's all automated. It's a simple system of timestamps. Each time a customer renews his or her DHCP lease and gets a new IP address, the change gets recorded. To find out what a certain customer's IP address was at a certain time, you would just look at the list, find the customer's name, ID, or account number (or whatever they use to represent customers), enter in the time period you're interesting in and then you can see what IP address he or she had at that time.



Similarly, if you wanted to find out which customer a certain IP address could be linked to, you'd enter in the time period and IP address and you could find out the name or account number of the customer who had it at that time.



Surprisingly simple, right?How does ISP trace an IP address if it can be changed constantly?
About all you can change are your local IP addresses -- the ones that probably start off 192.168.xxx.xxx. These are all on your local area network: your computers, your router, possibly game devices and iPods.



But your router has another IP address that the Internet sees and your local area network never sees. This is assigned by your ISP and you can't change it. If you did, your ISP wouldn't know who it was talking to and would ignore you.



So the ISP tracks IP addresses simply by virtue of having the power to assign them from its pool to its customers and by recording whenever it changes one.



Hope that helps.
Your changing your local IP. That is to say the one within your network. Also Each packet of information that you send out contains where it's going and who sent it via IP address.



The IP that is on the World Network aka the web is granted to you by the ISP therefore they know who you are. ISP's also keep a log of when there is activity on an IP.
xx.xxx is controlled by your ISP. Everything you do your ISP tracks and records! How they do it, is proprietary information!