I should have a dynamic IP, but it won't change

Question

I have run ipconfig /all, which tells me DHCP is enabled, meaning I should have a dynamic IP address. However, no matter how many times I restart the modem, I end up with the same IP address. What am I missing?

I am trying to configure the reconnect option for a program called jdownloader, but before that, first I have to be able to reconnect and change my IP manually, which I can't seem to do. Clicking on ip v4 option and going to properties shows that "Obtain IP adress automatically" is selected.

Solution

You're missing the fact that many DHCP servers, without further configuration, will give each device, as identified through its MAC address, the same IP address – even when they ask for a new lease.

Of course you can configure DHCP servers differently, but it's not uncommon for these leases to be reserved for a certain period of time, say a week, or a month. This is called reservation, and it may be enabled by default. It's just really useful: Imagine you take your laptop to work every day and then come back home. You will get the same IP address and won't have to look it up every time.

If you're talking about your router and your LAN IPs, look into its settings whether there's a table for IP address allocation that's automatically filled, and clear it. If you're talking about your external IP given to you by your ISP, there's not much you can change here, really. The ISP uses the MAC address of your modem (which they handed to you) to know it's you who connects. Changing the MAC address won't help you get a new IP—you just won't be able to connect to the Internet.

As @tictacbum correctly mentions, ipconfig will only show your LAN IP address, not the WAN address (the external IP). To check this, use any online service for that, or just Google.

Comments

[Bigbio2002]

Why do you want a new IP address? Who are you hiding from??

[adithya]

can you right click on your lan icon >> click on TCP\ip v4 option >> click on properties and tell me wether obtain ip dynamically is selected or static IP is selected.??

[Bankers Union]

I am trying to configure the reconnect option for a program called jdownloader, but before that, first I have to be able to reconnect and change my IP manually, which I can't seem to do. Clicking on ip v4 option and going to properties shows that "Obtain IP adress automatically" is selected.

[Psycogeek]

I use Jdownloader too, used to be able to aquire a new, but not any more. Mabey if i go back to dial-up :-)

[Bankers Union]

In my situation, it would really be more useful if I can reset my IP when I wish. How can I configure DHCP to disable reservation? I have a netgear WNR2000V1. I've checked it's settings, and it says Its configured to obtain IPs dynamically. However, since the IP isn't changing, I'm assuming it's because of the reservation system you mentioned.

[slhck]

Is it the external IP given to you by your ISP you want to allocate? Or just for your computer, e.g. 192.168.1.123?

[Zoredache]

@BankersUnion, You cannot change the DHCP server at all. There is nothing you can do with DHCP to change what you are givien. As slhck mentioned, DHCP associates the reserved IP with a particular MAC. Many routers router permit you to set a different MAC address. Simply update your MAC, and viola, new IP. Don't do that too much though, or your ISP will get annoyed at you.

[Bankers Union]

I would like to change the external IP given to me by my ISP.

[slhck]

@BankersUnion That's not doable unless you get a new MAC address for your modem, which basically is impossible and would require you to get a new modem. I'm pretty sure there's no point in trying to talk to the ISP to clear the IP reservations for you.

[Bankers Union]

I have tried changing my router's MAC address. However, that lead to my computer not being able to connect to the "DNS Server". Once I reverted to my previous MAC address, I was able to reconnect to the internet.

[Psycogeek]

What Slhck said, we dont even configure for the ISP anymore, they use that MAC address, require a call to even assign a new modem (aka new MAC). And spoofing and other tricks are out, if they spot those they could toss me off the network altogether. Owned. Picking up DNS as long as you have net, should be easy, DNS doesnt have to be supplied by the ISP, but it probably is deeper than that.

[Bankers Union]

So, there is no way to change my external IP, short of buying a new modem?

[slhck]

@BankersUnion Well, if your modem/router allows you to change (spoof) the MAC address, and this won't let you connect to the Internet, that's not surprising, because your ISP knows your MAC address (because they gave you that modem) and uses that to give you Internet access. I'm afraid you're out of options.

[Lluís]

are you sure your external IP is not changing? open checkip.dyndns.com reboot your router and check it again. ipconfig shows your local IP, I guess you are trying to change your external IP

[Bankers Union]

Damn, I guess it's time to consider getting a premium uploadedto account.

[Bankers Union]

Yup, checked it multiple times, my IP doesn't change at all.

[Scott - Слава Україні]

Can you explain this a little better?   Please do not respond in comments;  edit your answer to make it clearer and more complete.