On Thu, Jan 5, 2012 at 4:15 PM, Troy Adkins <[email protected]>
wrote:
> With my lack of IP subnetting knowledge. I have the following need.
>
> If I have 10.100.10.x network, a 10.100.11.x, and a 10.100.12.x..
>
> I need to expand my 10.100.11.x network from 254 to 508. Is that
possible?
Others have done a good job answering, but I wanted to add this
amplification: I find you look at the IP numbers in binary it will make a
lot more sense.
Say we're looking at host 10.100.11.42 on your network. The subnet mask
is 255.255.255.0, I presume. So the network part is the "10.100.11" at the
beginning and the host part is the "42" at the end. Write that out in
binary:
|<------ network ------->| | host |
010.100.011.042 = 00001010 01100100 00001011 00101010
255.255.255.000 = 11111111 01111111 11111111 00000000
010.100.011.000 = 00001010 01100100 00001011 00000000
000.000.000.042 = 00000000 00000000 00000000 00101010
Each 0 or 1 on the right side is a single bit. It can be only zero or
one, on or off.
See how the network portion of the netmask is all ones, and the host
portion is all zeros? That's what "netmask" means -- it masks the host
portion, leaving just the network.
The broadcast address on that network will be 10.100.11.255. Let's look
at that:
|<------ network ------->| | host |
010.100.011.255 = 00001010 01100100 00001011 11111111
255.255.255.000 = 11111111 01111111 11111111 00000000
010.100.011.000 = 00001010 01100100 00001011 00000000
000.000.000.255 = 00000000 00000000 00000000 11111111
As you can see, the broadcast address is all ones in the host portion.
That's the end of the network.
You'll also see "255.255.255.0" written as "/24". Count the number of
bits in the netmask, and you'll find it's 24. That's where that comes from.
If you want more hosts in your 10.100.11.42/24, you'll have to make the
host portion bigger, and the network portion smaller. Since your networks
numbers are currently adjacent, there's no room. You'll have to renumber
something.
For the sake of illustration, let's say you do that renumber, and in the
process, increase 10.100.11.0/24 to a new network with a /23 size -- one
bit bigger host portion. It won't start at 11 anymore, due to the way the
binary representation translates to decimal.
|<------ network ------>|| host |
255.255.252.000 = 11111111 01111111 11111110 00000000
010.100.010.000 = 00001010 01100100 00001010 00101010
In the above, note that the host portion is one bit bigger, and the
network portion thus one bit smaller. The new network is 10.100.10.0/23.
Because the network/host boundary is now in the middle of a byte, we
don't get the nice clean separation in decimal form. That's why those
digits in the middle of the dotted-decimal notation are a third color.
Let's look at a few hosts in this hypothetical new
10.100.10.0/23network, along with the broadcast address:
|<------ network ------>|| host |
255.255.252.000 = 11111111 01111111 11111110 00000000
010.100.010.001 = 00001010 01100100 00001010 00000001 A
010.100.010.042 = 00001010 01100100 00001010 00101010 B
010.100.010.255 = 00001010 01100100 00001010 11111111 C
010.100.011.000 = 00001010 01100100 00001011 00000000 D
010.100.011.042 = 00001010 01100100 00001011 00101010 E
010.100.011.254 = 00001010 01100100 00001011 11111110 F
010.100.011.255 = 00001010 01100100 00001011 11111111 G
In the above, I've added some letters at the end for ease of reference.
A is the first usable host address, F is the last usable host address. G
is the broadcast address -- the host portion is all ones.
Note that C ends in .255, but since the host portion is one bit bigger,
the host portion is *not* all ones. Thus it's a perfectly valid host
address. D is the next host in sequence. The computer doesn't care that
the decimal numbers look funny; C and D are right next to each other in
binary numbering.
Also compare B and E. Both end in .042, but the most significant bit
differs. So those are two different hosts.
I hope this helps explain the "why" behind the "what".
-- Ben
~ Finally, powerful endpoint security that ISN'T a resource hog! ~
~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~
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