subnetting confusion

My network has 70 PCs on it. I am using a Class C private IP addresses
range (192.168.1.1-192.168.1.254) distributed via DHCP. My current subnet
mask is the default 255.255.255.0. My current IP address leases are
192.168.1.11 through 192.168.1.204 (with a few exclusions).
I am a bit confused about the whole concept of subnetting, private IP
address, network classes, etc, etc. Say I want to put seven of my computers
from the registration department on a different subnet, by adjusting their
subnet mask. How would I accomplish this? Is it correct to say that these
computers would no longer be able to communicate with computers with a
subnet mask of 255.255.255.0?
Are DHCP superscopes used to accomplish what I am talking about an easier
way?
Thanks in advance

> Say I want to put seven of my computers from the registration department
> on a different subnet, by adjusting their subnet mask.
> How would I accomplish this?

Just change their addresses.

Example 192.168.2.x Mask 255.255.255.0. THEN, put a router between them and
your other (sub)network.

> Is it correct to say that these computers would no longer be able to
> communicate with computers with a subnet mask of 255.255.255.0?

Yes, UNLESS you ad the router to route between them.

> Are DHCP superscopes used to accomplish what I am talking about an easier
> way?

No need for superscopes.

Why don't you tell us your desired outcome? What's the point? What do you
want to do?

-Frank

Thanks for the reply.
What I want to do is get a better understanding of when and why changing a
subnet mask is or is not necessary. I am looking possibly at a better way
to organize my network, which is relatively small. Would there be any
benefits of doing something like (other than organization) assigning
printers on IP address ranges of 192.168.1.x and computers in registration
department 192.168.2.x and computers in finance department 192.168.3.x and
so on.
For your example you are keeping the default subnet mask. So you are saying
that without a router a computer with an IP address of 192.168.1.1 can not
communicate with a computer having an IP address of 192.168.2.1 even if the
subnet masks are the same?
Maybe my confusion lays in the fact that there are always several ways to
accomplish the same thing.
Change subnet mask if you want to accomplish (like running out of IP
addresses) this, this, or this.
Just change IP address (as in your example) if you want to do this, this or
this.
Use superscope if you want to do this, this or this.
Or do a combination of all of the above.
just trying to get a grasp on the big picture really.
"Frankster" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ...
>> Say I want to put seven of my computers from the registration department
>> on a different subnet, by adjusting their subnet mask.
>> How would I accomplish this?
>
> Just change their addresses.
>
> Example 192.168.2.x Mask 255.255.255.0. THEN, put a router between them
> and your other (sub)network.
>
>> Is it correct to say that these computers would no longer be able to
>> communicate with computers with a subnet mask of 255.255.255.0?
>
> Yes, UNLESS you ad the router to route between them.
>
>> Are DHCP superscopes used to accomplish what I am talking about an easier
>> way?
>
> No need for superscopes.
>
> Why don't you tell us your desired outcome? What's the point? What do
> you want to do?
>
> -Frank
>

I would not recommend setting up a set of subnets on a network as small as
yours unless there are geographical reasons why... if you have several
departments you can use Active Directory to establish small work groups with
regards to shares from both the server and peer-to-peer if need be as well as
printers. By adding the subnets you are going to add another layer of
complication as well as equipment. Where Active Directory has many tools at
your disposal that just need to be brushed up on and you will be good to go.

Oh... and I have looked into doing just this same thing for some of my
networks as I learned more about IP as well... so don't feel alone... there
are many neet things that "can" be done with IP... but I always ask myself
how else can I get this done and what is it that I am trying to accomplish...
then I choose the most simplistic approach.

Aaron Neunz wrote:
>Thanks for the reply.
>What I want to do is get a better understanding of when and why changing a
>subnet mask is or is not necessary. I am looking possibly at a better way
>to organize my network, which is relatively small. Would there be any
>benefits of doing something like (other than organization) assigning
>printers on IP address ranges of 192.168.1.x and computers in registration
>department 192.168.2.x and computers in finance department 192.168.3.x and
>so on.
>For your example you are keeping the default subnet mask. So you are saying
>that without a router a computer with an IP address of 192.168.1.1 can not
>communicate with a computer having an IP address of 192.168.2.1 even if the
>subnet masks are the same?
>Maybe my confusion lays in the fact that there are always several ways to
>accomplish the same thing.
>Change subnet mask if you want to accomplish (like running out of IP
>addresses) this, this, or this.
>Just change IP address (as in your example) if you want to do this, this or
>this.
>Use superscope if you want to do this, this or this.
>Or do a combination of all of the above.
>just trying to get a grasp on the big picture really.
>>> Say I want to put seven of my computers from the registration department
>>> on a different subnet, by adjusting their subnet mask.
>[quoted text clipped - 19 lines]
>>
>> -Frank

--
Message posted via WinServerKB.com
http://www.winserverkb.com/Uwe/Forum...rking/200512/1

> What I want to do is get a better understanding of when and why changing a
> subnet mask is or is not necessary.

You are correct in your assumption that you can carve out a subnet from you
existing network (alienate) by simply changing the mask. You can also do it
by changing the IP to be outside of the same mask. But, you do have to
understand how this works.

A mask of 255.255.255.0 means that to be on the same network (subnet), the
first three octets have to be the same. The fourth octet can be anything, up
to 254. If you change a machine's address to be
same.same.different.different, he will be off your network (on it's own
subnet). It will not be able to communicate with the original network unless
you place a router between them and manually forward the networks back and
forth.

You could also change the mask. For this, I need an IP calculator (crutch)
because I am not that good at it. However, I will use my own scenario as an
example because know it is right.

I have purchased a set of 8 static IPs. My ISP gave me the IPs, told me
which one to assign to my router, which one was used to define the network,
which one to assign to my firewall (using 3 total at this point). That
leaves me 5 I can use internally for the machines where I want to have
public IPs (not often, but it happens). So... Here is what I use:
IPs 61.50.80.45 to 61.50.80.52. You'll notice that is 8 total IPs (I made
them up for this post...hehe...). Anyway, my mask is 255.255.255.248
(really mine). The ending 248 limits my (sub)network to only those 8
addresses. If I configured an address out of that range he would be off the
original network. In this case, you are subneting using a mask.

The actual IP and the mask have both got to be taken into consideration to
determine if you are on the same subnet or not. You can't tell with just
one.

> I am looking possibly at a better way to organize my network

Use AD and OUs in Windows. Don't bother with subnets unless you can absorb
the costs of a router between each subnet.

> Maybe my confusion lays in the fact that there are always several ways to
> accomplish the same thing.

Yes, probably.

> just trying to get a grasp on the big picture really.

Suggest a good read from the bookstore or online about TCP/IP. It's all
based on binary math. Kinda tedious but helps in the long run.

-Frank

Very well put Frank... I think I need a little practice giving written advice.
... but I like what you put down here and hope that there is some stuff here
that helps Aaron...

Frankster wrote:
>> What I want to do is get a better understanding of when and why changing a
>> subnet mask is or is not necessary.
>
>You are correct in your assumption that you can carve out a subnet from you
>existing network (alienate) by simply changing the mask. You can also do it
>by changing the IP to be outside of the same mask. But, you do have to
>understand how this works.
>
>A mask of 255.255.255.0 means that to be on the same network (subnet), the
>first three octets have to be the same. The fourth octet can be anything, up
>to 254. If you change a machine's address to be
>same.same.different.different, he will be off your network (on it's own
>subnet). It will not be able to communicate with the original network unless
>you place a router between them and manually forward the networks back and
>forth.
>
>You could also change the mask. For this, I need an IP calculator (crutch)
>because I am not that good at it. However, I will use my own scenario as an
>example because know it is right.
>
>I have purchased a set of 8 static IPs. My ISP gave me the IPs, told me
>which one to assign to my router, which one was used to define the network,
>which one to assign to my firewall (using 3 total at this point). That
>leaves me 5 I can use internally for the machines where I want to have
>public IPs (not often, but it happens). So... Here is what I use:
>IPs 61.50.80.45 to 61.50.80.52. You'll notice that is 8 total IPs (I made
>them up for this post...hehe...). Anyway, my mask is 255.255.255.248
>(really mine). The ending 248 limits my (sub)network to only those 8
>addresses. If I configured an address out of that range he would be off the
>original network. In this case, you are subneting using a mask.
>
>The actual IP and the mask have both got to be taken into consideration to
>determine if you are on the same subnet or not. You can't tell with just
>one.
>
>> I am looking possibly at a better way to organize my network
>
>Use AD and OUs in Windows. Don't bother with subnets unless you can absorb
>the costs of a router between each subnet.
>
>> Maybe my confusion lays in the fact that there are always several ways to
>> accomplish the same thing.
>
>Yes, probably.
>
>> just trying to get a grasp on the big picture really.
>
>Suggest a good read from the bookstore or online about TCP/IP. It's all
>based on binary math. Kinda tedious but helps in the long run.
>
>-Frank

--
Message posted via WinServerKB.com
http://www.winserverkb.com/Uwe/Forum...rking/200512/1

> Very well put Frank... I think I need a little practice giving written
> advice... but I like what you put down here and hope that there is
> some stuff here that helps Aaron...

Thanks.

Hehe.... Obtaining my MCSE, 5 years as an electronics instructor, 10 years
as a flight instructor and 15 years as an IT manager helps a little :-)

-Frank

Indeed Frank... I have many years in the IT industry... none of which have
been spent training... keep up the good work :Þ

Frankster wrote:
>> Very well put Frank... I think I need a little practice giving written
>> advice... but I like what you put down here and hope that there is
>> some stuff here that helps Aaron...
>
>Thanks.
>
>Hehe.... Obtaining my MCSE, 5 years as an electronics instructor, 10 years
>as a flight instructor and 15 years as an IT manager helps a little :-)
>
>-Frank

--
Message posted via http://www.winserverkb.com

This is starting to make sense to me. I appreciate your replies.
I do utilize organizational units with my current network configuration.
I found a pretty neat calculator at:
http://www.subnetmask.info/
Do you know of a calculator in which you can input IP addresses and subnet
masks to determine if the nodes are on the same network?
This ANDing stuff is for the birds...
Thanks for the help fellas!!

"J.Couch via WinServerKB.com" <u14461@uwe> wrote in message
news:58db4b5c76fe6@uwe...
> Indeed Frank... I have many years in the IT industry... none of which have
> been spent training... keep up the good work :Þ
>
> Frankster wrote:
>>> Very well put Frank... I think I need a little practice giving written
>>> advice... but I like what you put down here and hope that there is
>>> some stuff here that helps Aaron...
>>
>>Thanks.
>>
>>Hehe.... Obtaining my MCSE, 5 years as an electronics instructor, 10 years
>>as a flight instructor and 15 years as an IT manager helps a little :-)
>>
>>-Frank
>
> --
> Message posted via http://www.winserverkb.com

"Aaron Neunz" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> Thanks for the reply.
> What I want to do is get a better understanding of when and why changing a
> subnet mask is or is not necessary.

That is easy. If you have less than 250-300 Hosts and have no "special"
security situation requiring segmentation,...then don't do it.

Layer3 Segment do to things,..they provide the means to use ACLs on a Router
between the segments,...and they prevent "broadcasts" from spreading futher
then they need to. So if you don't have any broadcast issues (you couldn't
possibly with only 70 machines) and have no special reasons for Router
ACLs,...then forget it.

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
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