subnet question

I have a general understanding of subnetting. For example given a question
such as:

You have this network 192.168.0.0/24. You must create at least 4 subnets
that can accomodate up to 20 hosts each. What subnet should you assign to
the hosts on your network?

This is an actual question I have done on a practice exam. I can break down
to binary and come up with the 255.255.255.224 subnet mask using simple math
(2 to the x power - 2 = z, x being bits, z being number of hosts, or
subnets, depending on what your trying to figure out) But I don't fully
undertand the application of this? when it says "what subnet should you
assign to the hosts on your network?" it seems they mean that that one
subnet 255.255.255.224 should be assigned to ALL hosts on ALL those
subnets??? is that correct? I was thinking that each individual subnet mask
would need to be used on each individual subnet??? Meaning if you are taking
3 extra bits from your hosts bits to use as additional subnets then wouldn't
each of those subnets have its own unique subnet mask? and wouldn't you need
to assign each unique subnet mask to the hosts on that unique subnet?? ..
and NOT have all hosts among the 3 different subnets have the SAME subnet
mask?

Hopefully I asked that clearly... Any info is greatly appreciated.
Thanks.

"djc" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> I have a general understanding of subnetting. For example given a
question
> such as:
>
> You have this network 192.168.0.0/24. You must create at least 4 subnets
> that can accomodate up to 20 hosts each. What subnet should you assign to
> the hosts on your network?

They all would typically have the same subnet mask. the actual subnet they
are in is "acknoledged" by which "range" their address falls in.

> to binary and come up with the 255.255.255.224 subnet mask using simple
math
> (2 to the x power - 2 = z, x being bits, z being number of hosts, or
> subnets, depending on what your trying to figure out)

Simple math? How about some simpler math?....The valid subnet host sizes
are always 128, 64, 32, 16, 8, 4, assuming you are working in the fourth
octet. So if you want 20 hosts, you subtract 32 from 256 and you get 224,
whala! there is your subnet mask. If you already have the mask and want to
know how many hosts are in each subnet, then subtract the mask from 256
(256-224=32) and you get 32, whala!,...you have the maximum host addresses
provided by that subnet.


--

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

DJC,

What they are looking for here is your ability to figuure out which
subnet mask fits their requirement. Yes, you would use the same
subnet mask for all clients (in this example). For instance, if you
had a subnet mask of 255.255.255.128 that you wanted to use for your
10.10.10.x address space to have two network segments, one segment
would exist from 10.10.10.0 - .127 and one segement would exist
between 10.10.10.128 - 255, but all clients on either network segment
would use 255.255.255.128 for their network mask.

You have probably seen questions that test your subnet knowledge in a
slightly different way. These questions will give you a mask and a
host address. From this you need to find the network address, the
broadcast address and maybe the first and last usable address.

"djc" <(E-Mail Removed)> wrote in message news:<#(E-Mail Removed)>...
> I have a general understanding of subnetting. For example given a question
> such as:
>
> You have this network 192.168.0.0/24. You must create at least 4 subnets
> that can accomodate up to 20 hosts each. What subnet should you assign to
> the hosts on your network?
>
> This is an actual question I have done on a practice exam. I can break down
> to binary and come up with the 255.255.255.224 subnet mask using simple math
> (2 to the x power - 2 = z, x being bits, z being number of hosts, or
> subnets, depending on what your trying to figure out) But I don't fully
> undertand the application of this? when it says "what subnet should you
> assign to the hosts on your network?" it seems they mean that that one
> subnet 255.255.255.224 should be assigned to ALL hosts on ALL those
> subnets??? is that correct? I was thinking that each individual subnet mask
> would need to be used on each individual subnet??? Meaning if you are taking
> 3 extra bits from your hosts bits to use as additional subnets then wouldn't
> each of those subnets have its own unique subnet mask? and wouldn't you need
> to assign each unique subnet mask to the hosts on that unique subnet?? ..
> and NOT have all hosts among the 3 different subnets have the SAME subnet
> mask?
>
> Hopefully I asked that clearly... Any info is greatly appreciated.
> Thanks.

I do like your math! but I need to review subnetting! I just need this last
piece to completely grasp it.
thanks for the reply!

"Phillip Windell" <@.> wrote in message
news:%(E-Mail Removed)...
> "djc" <(E-Mail Removed)> wrote in message
> news:%(E-Mail Removed)...
> > I have a general understanding of subnetting. For example given a
> question
> > such as:
> >
> > You have this network 192.168.0.0/24. You must create at least 4 subnets
> > that can accomodate up to 20 hosts each. What subnet should you assign
to
> > the hosts on your network?
>
> They all would typically have the same subnet mask. the actual subnet
they
> are in is "acknoledged" by which "range" their address falls in.
>
> > to binary and come up with the 255.255.255.224 subnet mask using simple
> math
> > (2 to the x power - 2 = z, x being bits, z being number of hosts, or
> > subnets, depending on what your trying to figure out)
>
> Simple math? How about some simpler math?....The valid subnet host
sizes
> are always 128, 64, 32, 16, 8, 4, assuming you are working in the fourth
> octet. So if you want 20 hosts, you subtract 32 from 256 and you get 224,
> whala! there is your subnet mask. If you already have the mask and want
to
> know how many hosts are in each subnet, then subtract the mask from 256
> (256-224=32) and you get 32, whala!,...you have the maximum host addresses
> provided by that subnet.
>
>
> --
>
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
>
>

Thanks for the example... its starting to click now. My biggest issue is
being in and out of this... I just need to follow it through to complete
understanding and be done with it... actually, and then move on to IPv6...

thanks again.

"JD Williams" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> DJC,
>
> What they are looking for here is your ability to figuure out which
> subnet mask fits their requirement. Yes, you would use the same
> subnet mask for all clients (in this example). For instance, if you
> had a subnet mask of 255.255.255.128 that you wanted to use for your
> 10.10.10.x address space to have two network segments, one segment
> would exist from 10.10.10.0 - .127 and one segement would exist
> between 10.10.10.128 - 255, but all clients on either network segment
> would use 255.255.255.128 for their network mask.
>
> You have probably seen questions that test your subnet knowledge in a
> slightly different way. These questions will give you a mask and a
> host address. From this you need to find the network address, the
> broadcast address and maybe the first and last usable address.
>
> "djc" <(E-Mail Removed)> wrote in message
news:<#(E-Mail Removed)>...
> > I have a general understanding of subnetting. For example given a
question
> > such as:
> >
> > You have this network 192.168.0.0/24. You must create at least 4 subnets
> > that can accomodate up to 20 hosts each. What subnet should you assign
to
> > the hosts on your network?
> >
> > This is an actual question I have done on a practice exam. I can break
down
> > to binary and come up with the 255.255.255.224 subnet mask using simple
math
> > (2 to the x power - 2 = z, x being bits, z being number of hosts, or
> > subnets, depending on what your trying to figure out) But I don't fully
> > undertand the application of this? when it says "what subnet should you
> > assign to the hosts on your network?" it seems they mean that that one
> > subnet 255.255.255.224 should be assigned to ALL hosts on ALL those
> > subnets??? is that correct? I was thinking that each individual subnet
mask
> > would need to be used on each individual subnet??? Meaning if you are
taking
> > 3 extra bits from your hosts bits to use as additional subnets then
wouldn't
> > each of those subnets have its own unique subnet mask? and wouldn't you
need
> > to assign each unique subnet mask to the hosts on that unique subnet??
...
> > and NOT have all hosts among the 3 different subnets have the SAME
subnet
> > mask?
> >
> > Hopefully I asked that clearly... Any info is greatly appreciated.
> > Thanks.

"djc" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I do like your math! but I need to review subnetting! I just need this
last
> piece to completely grasp it.

Unless I misunderstood the question, I think I answered it. Yes, all hosts
typically would use the same subnet.

However at the risk of confusing you, there are exceptions, such as
additional splitting of the last subnet because the last subnet of every
split is not usable unless it is itself futher split into smaller subnets.
The best example would be a network using 192.168.1.0 255.255.255.128. This
splits the network into two subnets of 128 hosts each:

#1 192.168.1.0 -- 192.168.1.127
#2 192.168.1.128 -- 192.168.1.255

However the second subnet (the last subnet) is not usable because it
contains the "Master Broadcast Address" of 192.168.1.255. Therefore the
second subnet must be further split into additional subnets which will cause
there to be a different mask for members of those resulting subnets. So you
take that second subnet (last subnet) and split it into "64 host" subnets,
the repeat the process with the "new" last subnet and split it into subnets
of "32 hosts". You continue to repeat the process untill your needs are
met or you reach the final "4 host" subnet.

A "4 host" subnet is used for WAN links, like a T1 with a router at each
end. In a "4 host" network the first address is reserved as a Network ID
and the fourth (last) address is reserved as the Broadcast Address which
leaves you with only two usable addresses. The two addresses are then given
to the router at each end of the T1.

The last "4 host" subnet that contains 192.168.1.255, of course, is not
usable, but at least this time you have only lost 4 addresses instead of 128
addresses.

--

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

The practice of losing the last subnet is required for rfc950
interoperability and only need be followed if non-rfc1812 compliant devices
are present on the network (highly unlikely).

http://www.ipprimer.com/addressing.cfm

you did answer my specific question. Thank you. I just meant I feel there is
one last piece, in 'general' to subnetting that I still need to completely
grasp the whole subject. I am confused by your additional info though it is
welcome... I knew that the first and last host addresses were not usable as
they are the network ID and broadcast addresses, respectively, but I had not
known that the entire last subnet is not usable.. this, I don't
understand... yet.

thanks again!

"Phillip Windell" <@.> wrote in message
news:%(E-Mail Removed)...
> "djc" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > I do like your math! but I need to review subnetting! I just need this
> last
> > piece to completely grasp it.
>
> Unless I misunderstood the question, I think I answered it. Yes, all hosts
> typically would use the same subnet.
>
> However at the risk of confusing you, there are exceptions, such as
> additional splitting of the last subnet because the last subnet of every
> split is not usable unless it is itself futher split into smaller subnets.
> The best example would be a network using 192.168.1.0 255.255.255.128.
This
> splits the network into two subnets of 128 hosts each:
>
> #1 192.168.1.0 -- 192.168.1.127
> #2 192.168.1.128 -- 192.168.1.255
>
> However the second subnet (the last subnet) is not usable because it
> contains the "Master Broadcast Address" of 192.168.1.255. Therefore the
> second subnet must be further split into additional subnets which will
cause
> there to be a different mask for members of those resulting subnets. So
you
> take that second subnet (last subnet) and split it into "64 host" subnets,
> the repeat the process with the "new" last subnet and split it into
subnets
> of "32 hosts". You continue to repeat the process untill your needs are
> met or you reach the final "4 host" subnet.
>
> A "4 host" subnet is used for WAN links, like a T1 with a router at each
> end. In a "4 host" network the first address is reserved as a Network ID
> and the fourth (last) address is reserved as the Broadcast Address which
> leaves you with only two usable addresses. The two addresses are then
given
> to the router at each end of the T1.
>
> The last "4 host" subnet that contains 192.168.1.255, of course, is not
> usable, but at least this time you have only lost 4 addresses instead of
128
> addresses.
>
> --
>
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
>
>
>

thanks for the additional info.. I'll check it out.

"Dodo" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> The practice of losing the last subnet is required for rfc950
> interoperability and only need be followed if non-rfc1812 compliant
devices
> are present on the network (highly unlikely).
>
> http://www.ipprimer.com/addressing.cfm
>
>

http://ralphb.net/IPSubnet/