Subscriber Joseph Murphy wrote to ask:
I am wondering how an IP address is determined and if it can be changed and how?
Thank you, J. P. Murphy.
That’s a good question, Joseph. The answer can be simple or it can be used to educate.
Whether you access your home network or access your Internet Service Provider’s network as a method to get to the Internet, the basic answer is that the IP address you use to access a network is assigned by the network administrator or by his DHCP (Dynamic Host Control Protocol) server.
You may get assigned a static IP address, in which case you’re told to set your computer or router to use the specific IP address that’s been assigned to you. You’re also provided with the netmask to be used and, perhaps, the specific computer name to use.
Your ISP may also require the Media Access Control Address (MAC Address) of the piece of hardware that connects to their system. In that circumstance, they’re usually controlling access to their network by the MAC Address, or the combination of MAC Address and IP address.
More often, you will get your IP address assigned by DHCP, in which case you’re told to set your computer’s network connection (or router, if you have one) to get its IP address from the ISP’s network via DHCP, so it will be automatically assigned.
At first blush, DHCP might seem to be a way to get varying IP addresses. After all, the DHCP server actually "leases" the IP address to a specific MAC Address for a specific period, often 24 hours. However, at the end of that period, the computer (or router) with the IP address will ask for a renewal of its IP address. If that address is not currently in use, the DHCP server will assign it again for a new lease period.
In that manner, the DHCP often will give a specific computer (or router) the same IP address over and over — simply because the license expired and that computer was the first one to say "I want to renew my license to IP address XXX.YYY.ZZZ.AAA, or give me an new one if that one is in use." Of course, the computer (or router) really doesn’t say all that, it just sends the signal saying it wants to renew its lease.
So, how can you get a different IP address?
First, if you’ve got a static IP address, you can contact your ISP and request a different one. They’ll probably want to know why. They might or might not be interested in giving you a different IP address.
If you’ve got a dynamic IP address, I think the easiest way to do that might be to get a different network card (if you aren’t using a router — and you SHOULD be using a router for security purposes), so it will have a different MAC Address (they’re unique for each individual network-capable piece of hardware).
If you’re using a router, most routers will let you specify the MAC Address that’s presented to the Internet side of the router (as opposed to the home network side). The purpose of that was to enable the user to change hardware without having to go through reconnection efforts with the cable or DSL Internet Service Provider.
What if you’ve got a combination DSL Modem + Router? In that case, you may not be able to change the MAC Address of the router. Since the router gets the Internet IP address, or whatever IP address is assigned by the ISP, you’re stuck with what they’ll will do for you.
All that seems confusing, which is why most ISP’s use DHCP for IP address assignment – so they won’t have to debug for their customers as often.