Member Avatar for John A

Hi, this never really bothered me before, but now it sort of does. My ADSL connection's IP address is DHCP assigned, and when I first got it, I just plugged it into my Mac, and it worked painlessly, so I never gave it much more thought.

But one thing I did notice is that my IP address always stays the same; it never changes even when my computer and modem are turned off (and I don't have a router either). So I just thought, "My ISP probably just gives out a permanant IP address to each of their customers.".

But I realized that it can't be true, because when I tried switching my internet connection to my Slackware Linux box, I got a totally different IP address!

And don't start on about the MAC addresses. My Slackware Linux box also had Windows on it, and when I boot into Windows, I get the same IP address that I get on my Macintosh.

I want to change my IP address for security reasons. You know, some websites log your IP address, and you want to keep your anonymity.

So, my question is: how do I change my DHCP assigned IP address? Here is my setup (the same on both Slackware and Tiger):

IP address: DHCP assigned
Hostname: Default (ISP assigned)
Subnet: Default (ISP assigned)
Router: Default (ISP assigned)

Any help would be appreciated. :)

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Dani AI

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A short, practical summary and a few extra pointers that build on what , and already said.

The reason an ISP-assigned DHCP address often “stays the same” is that DHCP servers hand out leases and remember the client identifier (typically the NIC’s MAC or the client DUID) until the lease expires or is released. For many consumer links the provider’s DHCP will either give long leases or associate the address with the modem/router MAC, so the same device gets the same public IP repeatedly. (manpages.debian.org)

Practical ways to request a different address (ordered from least to most intrusive):

  • Try a normal DHCP renew on the machine first (GUI or command line). On macOS you can use the Network settings → Details → TCP/IP → “Renew DHCP Lease” or run the ipconfig commands in Terminal. 

    sudo ipconfig set en0 BOOTP
sudo ipconfig set en0 DHCP

    (replace en0 with your interface). (support.apple.com)

  • On Linux use your DHCP client to release and re-request a lease. Example with isc-dhclient: 

    sudo dhclient -r eth0
sudo dhclient eth0

    (use the actual interface name or your distro’s client). (manpages.debian.org)

  • If the ISP ties the assignment to the WAN MAC, changing the WAN MAC (router “MAC clone” / spoof) and then forcing a renew or rebooting the modem will usually produce a different public IP. Most consumer routers expose a “MAC Address Clone” or WAN MAC field in the admin UI; set a new MAC, save, then power-cycle the modem/router. Be aware some ISPs will block unknown MACs until their provisioning clears. (kb.netgear.com)

A final note about anonymity: simply changing your IP rarely gives real anonymity (sites can use cookies, logins, browser fingerprints, and ISPs hold connection logs). For stronger privacy, use well-configured privacy tools such as Tor or a reputable VPN — Tor for high anonymity use-cases, VPNs for broader convenience — but read each tool’s limitations before relying on it. (tpo.pages.torproject.net)

If the goal is persistent privacy rather than a one-off address change, recommend the Tor Browser or a vetted VPN rather than MAC tricks; for troubleshooting a stubborn lease, contact the ISP (they can tell you lease length or clear the binding).

Recommended Answers

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Member Avatar for TheNNS

I dont' think you can change the address your ISP is giving you. But if you say that it's dynamic it should change. I would talk to your ISP about this.

Member Avatar for cbemerine

While you are stuck with the MAC address (or IP address) that your service provider gives you, what about using a software tool to hide who you are.

http://www.anonymizer.com/ - it would cost you $29.95, but it would hide who you are. My guess is you know about it already.

I honestly do not know of a way to hide your IP / MAC address and still have DNS resolve. If it is possible I would like to know how too.

Another program:
- offers free program as of Sept 27, 2006, but states some features are not available unless you register. I have not used either this or the Anonymizer.

Member Avatar for TheNNS

While you are stuck with the MAC address (or IP address) that your service provider gives you

ISP's don't provide you with a MAC address, the NIC has it built in, so it'll never change and there's not 2 NIC's with the same address.

Member Avatar for John A

I should note that I have a router now, and to change my IP address I simply change my MAC address and do a DHCP renew a few times, and I can get a new one. So it's solved.

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