IP Subnet Mask Advice Sought

Hi,

What exactly is a SUBNET, and what is it used for?

I have just noticed that the subnet mask of my router is set to
'255.255.255.0', but the subnet settings in a couple of computers connected
to my wireless network are set to 255.255.0.0

Although I have thus far not noticed any problems with accessing any
services on the network, what is the likely problems of having the subnet
not matching between the computers and the router? Advice on this would be
very welcome.

I'm a little bit confused about subnets altogether, and I'm not sure how
they need to be set, or what effects I would get if I don't have matching
subnets, so any advice on subnets, and how they work or have to be set up
would be very much appreciated.

Thanks a lot

On Sun, 22 Jan 2006 17:47:50 -0000, "George"
<george6no-(E-Mail Removed)> wrote:

>What exactly is a SUBNET, and what is it used for?

to divide the IP address into a part that identifies the network (or
sub-network) and the individual machines.

255.255.255.0 means only the last part of the IP identifies the
machine

255.0.0.0 means the last three parts, and so on.

255 in binary is 11111111 and this is used as a mask so 255.255.0.0
means 11111111.11111111.00000000.00000000

think of the zeros as holes in the mask through which you can see a PC

What difference does it make ?

take two IP s - 192.168.0.1 and 192.168.1.1

if the mask is 255.255.255.0 these are on two different subnets and
would need a router to communicate. If the mask is 255.255.0.0 they
are on the same subnet and can chat happily.

Phil
--

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"Phil Thompson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Sun, 22 Jan 2006 17:47:50 -0000, "George"
> <george6no-(E-Mail Removed)> wrote:
>
> >What exactly is a SUBNET, and what is it used for?
>
> to divide the IP address into a part that identifies the network (or
> sub-network) and the individual machines.
>
> 255.255.255.0 means only the last part of the IP identifies the
> machine
>
> 255.0.0.0 means the last three parts, and so on.
>
> 255 in binary is 11111111 and this is used as a mask so 255.255.0.0
> means 11111111.11111111.00000000.00000000
>
> think of the zeros as holes in the mask through which you can see a PC
>
> What difference does it make ?
>
> take two IP s - 192.168.0.1 and 192.168.1.1
>
> if the mask is 255.255.255.0 these are on two different subnets and
> would need a router to communicate. If the mask is 255.255.0.0 they
> are on the same subnet and can chat happily.
>
> Phil

So am I right in thinking, that following this rule, if the subnet mask was
255.0.0.0, then the following IPs would be able to chat happily too?
192.168.0.1 - 192.167.0.1 - 192.168.1.1?

Do I have that right Phil??

So is there any problem in running a subnet mask of 255.255.255.0 on my
router (on 192.168.0.1) and running a subnet of 255.255.0.0 on the computers
connected to it?

Am I right in thinking that if all your network IP addresses follow each
other, like 192.168.0.1, 192.168.0.2, 192.168.0.3, 192.168.0.4,
192.168.0.5, etc etc, then the subnet mask needs to be just set to
255.255.255.0 ????

Thanks Phil.....

George

In article <(E-Mail Removed)>,
"George" <george6no-(E-Mail Removed)> wrote:
>
> So am I right in thinking, that following this rule, if the subnet mask was
> 255.0.0.0, then the following IPs would be able to chat happily too?
> 192.168.0.1 - 192.167.0.1 - 192.168.1.1?
>
> Do I have that right Phil??

My name's not Phil, but you have that correct.

> So is there any problem in running a subnet mask of 255.255.255.0 on my
> router (on 192.168.0.1) and running a subnet of 255.255.0.0 on the computers
> connected to it?

That would be unusual - there may be reasons or doing something like
that, but more likely it's "incorrect" behaviour.

If the router is 192.168.0.1/255.255.255.0 and a PC
192.168.1.1/255.255.0.0 then the PC will think it's on the same subnet
as the router (and will send packets to it) but the router will think
it's on a different subnet and be unable to send packets to the PC (so
will try to gateway them through the ISP's router, which will fail).

> Am I right in thinking that if all your network IP addresses follow each
> other, like 192.168.0.1, 192.168.0.2, 192.168.0.3, 192.168.0.4,
> 192.168.0.5, etc etc, then the subnet mask needs to be just set to
> 255.255.255.0 ????

Yes. Normally so.

Stroller.