Unique IP Addresses

I'm living in a shared flat with two other people. I've got two PC's in my
room (one running Win2k, and the other running RH9 linux). My flatmates
have just one PC each running win2k. All the PC's are networked together,
and I have a router with firewall going out to the internet (ADSL). In the
past I've shared the internet connection with flatmates, but the current
flatmates aren't interested in splitting the costs of the connection. I've
got the firewall in the router blocking everything that doesn't come from my
PCs (192.168.0.2 (win2k) and 192.168.0.3 (linux)). I've tried changing my
win2k box's ip to 192.168.0.3, and it doesn't bark saying that a computer
already exists on the network with that IP. So there's nothing stopping a
flatmate changing his IP address, and gaining internet access. How can I
stop someone from using the same IP as me on my network?

Cheers for the info,
Dan.

In article <bue8ft$bge$1$(E-Mail Removed)>, "Dan"
(E-Mail Removed) says...
> I'm living in a shared flat with two other people. I've got two PC's in my
> room (one running Win2k, and the other running RH9 linux). My flatmates
> have just one PC each running win2k. All the PC's are networked together,
> and I have a router with firewall going out to the internet (ADSL). In the
> past I've shared the internet connection with flatmates, but the current
> flatmates aren't interested in splitting the costs of the connection. I've
> got the firewall in the router blocking everything that doesn't come from my
> PCs (192.168.0.2 (win2k) and 192.168.0.3 (linux)). I've tried changing my
> win2k box's ip to 192.168.0.3, and it doesn't bark saying that a computer
> already exists on the network with that IP.

That would be the Linux box, wouldn't it? Why would you want two
machines fighting over one address?

> So there's nothing stopping a
> flatmate changing his IP address, and gaining internet access. How can I
> stop someone from using the same IP as me on my network?
>
There may be a facility in your router to allocate address by MAC.

Soni tempori elseu romani yeof helsforo nisson ol sefini ill des Sun, 18 Jan
2004 15:24:34 -0000, sefini jorgo geanyet des mani yeof do
uk.comp.home-networking, yawatina tan reek esk "Dan" <(E-Mail Removed)> fornis
do marikano es bono tan el:

>I'm living in a shared flat with two other people. I've got two PC's inmy
>room (one running Win2k, and the other running RH9 linux). My flatmates
>have just one PC each running win2k. All the PC's are networked together,
>and I have a router with firewall going out to the internet (ADSL). In the
>past I've shared the internet connection with flatmates, but the current
>flatmates aren't interested in splitting the costs of the connection. I've
>got the firewall in the router blocking everything that doesn't come from my
>PCs (192.168.0.2 (win2k) and 192.168.0.3 (linux)). I've tried changing my
>win2k box's ip to 192.168.0.3, and it doesn't bark saying that a computer
>already exists on the network with that IP. So there's nothing stoppinga
>flatmate changing his IP address, and gaining internet access. How can I
>stop someone from using the same IP as me on my network?

Will the router let you restrict access by MAC address rather than IP?

deKay
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deKay wrote:
> Dan wrote
>>I'm living in a shared flat with two other people. I've got two PC's in my
>>room (one running Win2k, and the other running RH9 linux). My flatmates
>>have just one PC each running win2k. All the PC's are networked together,
>>and I have a router with firewall going out to the internet (ADSL). In the
>>past I've shared the internet connection with flatmates, but the current
>>flatmates aren't interested in splitting the costs of the connection. I've
>>got the firewall in the router blocking everything that doesn't come from my
>>PCs (192.168.0.2 (win2k) and 192.168.0.3 (linux)). I've tried changing my
>>win2k box's ip to 192.168.0.3, and it doesn't bark saying that a computer
>>already exists on the network with that IP. So there's nothing stopping a
>>flatmate changing his IP address, and gaining internet access. How can I
>>stop someone from using the same IP as me on my network?
>
>
> Will the router let you restrict access by MAC address rather than IP?
>
> deKay

If your flatmates are very clever, they can spoof MAC addresses too
while you are out, having determined yours while you're in.

A less techy solution is called for here, e.g. take some vital part of
the internet connection with you when you go out.
Presumably you let them connect to the router for gaming between you or
something, otherwise you could lock the router itself away.
Physical control is often easier than software control.
You could overcome the security limitations of your router by using your
Linux box for that purpose, with almost endless possibilities, coupled
with higher performance, too.

--
Have fun,
Mike
--
http://fonehelp.co.uk - PC support, no fix, no fee!

> If your flatmates are very clever, they can spoof MAC addresses too
> while you are out, having determined yours while you're in.

Unfortunetly, the router firewall doesn't support MAC addresses anyway. My
flatmates aren't that techy anyway. It's just that an IP change seems an
obvious thing to try.

> A less techy solution is called for here, e.g. take some vital part of
> the internet connection with you when you go out.
> Presumably you let them connect to the router for gaming between you or
> something, otherwise you could lock the router itself away.
> Physical control is often easier than software control.
> You could overcome the security limitations of your router by using your
> Linux box for that purpose, with almost endless possibilities, coupled
> with higher performance, too.

I presume when you say use the linux box - you mean as a proxy? I don't
really want to do that, cos I don't always have both machines on. I was
hoping on a more "operating system" solution - where I can get the operating
system to refuse to set an IP address that already exists on the network.
Is this not possible? Also, I don't understand why using the linux box
would have higher performance?

Thanks for any extra info,
Dan.

Dan wrote:
>>If your flatmates are very clever, they can spoof MAC addresses too
>>while you are out, having determined yours while you're in.
>
>
> Unfortunately, the router firewall doesn't support MAC addresses anyway. My
> flatmates aren't that techy anyway. It's just that an IP change seems an
> obvious thing to try.
>
>
>>A less techy solution is called for here, e.g. take some vital part of
>>the internet connection with you when you go out.
>>Presumably you let them connect to the router for gaming between you or
>>something, otherwise you could lock the router itself away.
>>Physical control is often easier than software control.
>>You could overcome the security limitations of your router by using your
>>Linux box for that purpose, with almost endless possibilities, coupled
>>with higher performance, too.
>
>
> I presume when you say use the linux box - you mean as a proxy?

No, as a masquerading router, plus caching DNS server and transparent
proxy, hence the "higher performance".
You'd just need a second NIC and to leave it on 24/7 (not the screen)
unless switching it off was your "flatmate blocker".
Cheap hardware routers are quite limited and slow, especially in latency
for online gaming.
Their security bugs are difficult to patch with firmware updates, too.

> I don't
> really want to do that, cos I don't always have both machines on. I was
> hoping on a more "operating system" solution - where I can get the operating
> system to refuse to set an IP address that already exists on the network.
> Is this not possible?

Yes, all operating systems refuse to adopt a duplicate ip, but when your
boxes are switched off, their ips are not being duplicated , are they?

Also, I don't understand why using the linux box
> would have higher performance?
See above
TCP/IP was a recent addition to Microshit systems and is still only
tacked onto them.
It is the very core of Unix systems, so they handle it far better.
Your router probably runs a Unix kernel of sorts, but a very limited one.



--
Have fun,
Mike
--
http://fonehelp.co.uk - PC support, no fix, no fee!

> Yes, all operating systems refuse to adopt a duplicate ip, but when your
> boxes are switched off, their ips are not being duplicated , are they?

This is basically the reason I sent the post initially. I tried to change
my win2k machine to the same IP as my linux box (192.168.0.3), and it didn't
bark saying that the IP was already on the network (the linux box was turned
on). I'm presuming that this is because they're different operating
systems? Presuming that both my linux box, and win2k box are always on - is
there any way to stop my flatmates setting their IP to the same as either
one of my boxes?

Cheers,
Dan.

Dan wrote:
>>Yes, all operating systems refuse to adopt a duplicate ip, but when your
>>boxes are switched off, their ips are not being duplicated , are they?
>
>
> This is basically the reason I sent the post initially. I tried to change
> my win2k machine to the same IP as my linux box (192.168.0.3), and it didn't
> bark saying that the IP was already on the network (the linux box was turned
> on). I'm presuming that this is because they're different operating
> systems?
No, it doesn't matter what OS is holding an ip address.

> Presuming that both my linux box, and win2k box are always on - is
> there any way to stop my flatmates setting their IP to the same as either
> one of my boxes?
>
Yes, it won't "bark", whatever operating system is already using that
address, so you don't need "any way" other than leaving your boxes on.
When you switch them off, unplug the router from the internet, presuming
it's in a locked room or cupboard.
If not and you need to switch off and go away, change the permitted ips
in the router (password protected settings) before you go and change
yours to those when you come back.

--
Have fun,
Mike
--
http://fonehelp.co.uk - PC support, no fix, no fee!

> Yes, it won't "bark", whatever operating system is already using that
> address, so you don't need "any way" other than leaving your boxes on.

I don't really understand what you mean by this. As my system currently
stands, one of my flatmates can change their own PC's IP address to
192.168.0.2, and be able to access the internet. This is even if my machine
(with .2 IP) is always turned on.

Dan.

Dan wrote:
>>Yes, it won't "bark", whatever operating system is already using that
>>address, so you don't need "any way" other than leaving your boxes on.
>
>
> I don't really understand what you mean by this. As my system currently
> stands, one of my flatmates can change their own PC's IP address to
> 192.168.0.2, and be able to access the internet. This is even if my machine
> (with .2 IP) is always turned on.
>
Oh sorry, yes, there is a difference with Windoze.
If someone attempts to use your ip address, a popup window asks if you
wish to allow it.
If you do allow it, your connection will be lost.
As Linux does not have the same popup protocols, it cannot allow it.
AFAIK the popup does not time-out, so unless they can OK it on your box,
they shouldn't be able to get in.


--
Have fun,
Mike
--
http://fonehelp.co.uk - PC support, no fix, no fee!