Ip addresses linked to MAC addresses?

Hi,
I recently decided to install a router onto my internet connection,
(partially because of my Shields Up results, and partially because my
linux computer acting as a router was a bottleneck (ISA ethernet cards.. eww))
Anyway, I plugged it in, booted it up, and noticed that my IP address had
changed. Now, nowhere in my internet access does it say anything about
static IP address, but my IP address hadn't changed for quite some time.
(Somewhere in the range of 1-2 years) I thought that this was too much of
a coincidence, so I took a closer look at my LinkSys router, and saw a WAN
mac address setting. I was curious, so I set it to the same as the mac
address of the card that was previously on the internet, and lo and
behold, back to my old IP address. This wouldn't have rung any alarm bells
in my mind, except for the first page you encounter when you click on the
Shields Up link; The one that says this:
The text below might uniquely identify you on the Internet
Your Internet connection's IP address is uniquely associated with 
the following "machine name":
h24-xxx-xxx-xxx.vn.shawcable.net
When I first read that page, I thought nothing of it, 'cause I recognized
my IP address imidiately, and went on to the port scan. 

Anyway, what I'm getting at is that perhaps the page about the "Reverse
DNS" should be changed to reflect this. For now though, I'm gonna have
some fun messing with my ISP by changing my mac address all the time.
(Hell, I could even automate it)

-Cody Y
0
Cody
9/3/2003 4:27:00 AM
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A MAC address cannot be spoofed... Can it?
0
Tusk
9/2/2003 8:02:00 PM
Yeah... That would count to me. ;-)

I just thought it was something that wasn't changeable...




"bloated_elvis" <thel8elvis@hotmail.com> wrote in message
news:MPG.19c0166e1d544b08989718@news.grc.com...
> In article <bj5h83$nim$1@news.grc.com>, onetwentyseven@zerozeroone.com
> says...
> > A MAC address cannot be spoofed... Can it?
> >
> Define 'spoofed' in a context. I can change my mac address. Does that
> count ?
>
> --
> Bloated Elvis
> http://www.frame4.com/php/downloads-cat-65.html
0
Tusk
9/2/2003 9:34:00 PM
In message <pan.2003.09.03.04.27.08.315662@dotat.at>, Cody Y 
<atdot@dotat.at> writes
>Anyway, what I'm getting at is that perhaps the page about the "Reverse 
>DNS" should be changed to reflect this.

Do you mean about the MAC address being tied to the IP? If so (and IIRC) 
the MAC address only goes one hop out, then is superseded by the MAC of 
the next bit of hardware. In any case it's not really traceable.

>For now though, I'm gonna have some fun messing with my ISP by changing 
>my mac address all the time. (Hell, I could even automate it)

Exercise caution. :-) Some ISPs tie the "registered" MAC address to your 
account/connection. I'm not sure if Shaw does it, but 
@Home/ATTbi/Comcast apparently does. Or at least did. They use that as 
one way to verify you/your computer. Perhaps related to an unenforced 
policy about multiple computers?

In any case, there have been a lot of reports of strange connection 
problems after installing routers, which went away once the MAC of the 
original, "registered" NIC was cloned into the router. YMMV.
-- 
 From invalid, Reply To works.
Kevin A.
0
Kevin
9/3/2003 4:59:00 AM
<snip>
> changed. Now, nowhere in my internet access does it say anything about
> static IP address, but my IP address hadn't changed for quite some time.
> (Somewhere in the range of 1-2 years) I thought that this was too much of
> a coincidence, so I took a closer look at my LinkSys router, and saw a WAN
> mac address setting. I was curious, so I set it to the same as the mac
> address of the card that was previously on the internet, and lo and
> behold, back to my old IP address.
<snip>

Many (most) DHCP servers around associate the "leased IP"
address to the client MAC, this is done to allow (as long as it's
possible) the same client to mantain the same IP but let's see
how this works (well more or less) let's say this is the first time
your machine connects to a network (or the internet) and that
it's configured to request DHCP infos

* Your machine connects to the net and sends out a DHCP
discover packet to find an available DHCP server

* The DHCP server answers, so your machine goes on and
asks to the DHCP server an IP address

* The DHCP server picks an IP address from its "free address
pool" and returns it to the client along with what's called the
"lease expiry time"

* The client confirms that it received/accepted the address

* The DHCP server records the IP along with the client MAC
into its "assigned addresses" pool


now you're on the network, at this point, let's say that the DHCP
server returned you a "lease expiry time" of 2 hours, this means
that after 2 hours the DHCP server will consider the IP address
as expired if it doesn't see a "renew" request, so your client will
dutifully send out such requests every (about) 3/4 of the lease
time, the DHCP server will also store your IP/MAC and keep it
even if the address expired, such an info will be kept as long as
the DHCP server doesn't run "out of free addresses" in such a
case, it will pick one (the oldest) of the expired addresses and
reuse it to assign an IP to a requesting client machine


now ... let's say that you switch off your machine for a full day (e.g.),
then you come back online and you repeat the above process, in
this case, the DHCP server will see a "known" MAC address and
will attempt to see if the previous IP address wasn't assigned to
another machine, if that's not the case, you'll get the same address,
otherwise you'll get a new address; at this point let's say that the DHCP
was configured to use a 7 days lease time, this means that you'll be
almost sure that as long as your MAC address doesn't change you'll
get the same IP, some ISPs prefer using high lease times so that the
DHCP traffic will be reduced, others keep a low lease time to avoid
the "almost static IP" effect (where a customer may setup servers as
if he has a static IP) others even "purge" the "reusable IPs" whenever
the lease time expires, so you'll get a new IP every time, in your
case I think that the ISP is using a long lease time, you may check
this by using "ipconfig /all" or "winipcgf" to see the lease infos

Hope it's clear now, btw there's more than just this, the DHCP will also
give to your client machine other infos such as the gateway address
the DNS servers addresses and so on, but that's outside the scope
of this post imo


-- 

* ObiWan

DNS "fail-safe" for Windows 2000 and 9X clients.
http://ntcanuck.com

408 XP/2000 tweaks and tips
http://ntcanuck.com/tq/Tip_Quarry.htm
0
ObiWan
9/3/2003 9:34:00 AM
"ObiWan" wrote
> Hope it's clear now

Thanks Obi, that made lots of sense, and cleared things up nicely for me.

Fuzzball
0
Fuzzball
9/3/2003 2:43:00 PM
I assume <---<<< ;-) that if your hardwired to a dialup modem, a mac change
is not possible?



> It's changeable in most new-ish ethernet cards, and even if it's not:
> http://www.klcconsulting.net/smac/ (for windows),
> in *nix it's as simple as using ifconfig.
>
> <>
>
> --
> Bloated Elvis
> http://www.frame4.com/php/downloads-cat-65.html
0
Tusk
9/3/2003 3:13:00 PM
Tusk� <onetwentyseven@zerozeroone.com> wrote:
> A MAC address cannot be spoofed... Can it?

If you could, it wouldn't do any good.  It gets dropped at the first border
router, from what I have read here.

-- 
Robert
List of Lists - http://lists.gpick.com/
Eric Howe's Privacy and Security Site -
http://www.staff.uiuc.edu/~ehowes/main-nf.htm
0
Robert
9/3/2003 8:07:00 PM
In article <bj5h83$nim$1@news.grc.com>, onetwentyseven@zerozeroone.com 
says...
> A MAC address cannot be spoofed... Can it?
> 
Define 'spoofed' in a context. I can change my mac address. Does that 
count ?

-- 
Bloated Elvis
http://www.frame4.com/php/downloads-cat-65.html
0
bloated_elvis
9/3/2003 8:17:00 PM
As far as I know, it's unchangable in ethernet cards, but it's
configurable for WAN only on my router. (I can't change the mac address of
the internal network)
-Cody
0
Cody
9/4/2003 3:05:00 AM
Cody Y wrote:
> As far as I know, it's unchangable in ethernet cards, but it's
> configurable for WAN only on my router. (I can't change the mac address of
> the internal network)
> -Cody

You *can* change the mac of cards, such as WIFI cards. Some brands even 
can be changed through the supplied software, others through the OS, 
etc. And, I can spoof a mac address to get access to a mac filtered AP. 
A little of the topic though.


Sean Kohlmeier
0
Sean
9/4/2003 7:16:00 AM
In article <pan.2003.09.04.03.05.11.381151@dotat.at>, atdot@dotat.at 
says...
> As far as I know, it's unchangable in ethernet cards, 

It's changeable in most new-ish ethernet cards, and even if it's not:
http://www.klcconsulting.net/smac/ (for windows),
in *nix it's as simple as using ifconfig.

<>

-- 
Bloated Elvis
http://www.frame4.com/php/downloads-cat-65.html
0
bloated_elvis
9/4/2003 11:41:00 AM
Tusk� <onetwentyseven@zerozeroone.com> wrote:
> I assume <---<<< ;-) that if your hardwired to a dialup modem, a mac
> change is not possible?

Dial-up modems don't have MAC addresses.  They have a generic one.

-- 
Robert
List of Lists - http://lists.gpick.com/
Eric Howe's Privacy and Security Site -
http://www.staff.uiuc.edu/~ehowes/main-nf.htm
0
Robert
9/4/2003 5:35:00 PM
Reply:

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