On Mon, 17 Jul 2000, James Wilson wrote:
> 11111111.11111111.11111111.11111110 255.255.255.254
> 11111111.11111111.11111111.11111111 255.255.255.255
These two are not valid netmasks - the first leaves you with no available
hosts {only two possible address - network and broadcast}, and the second
IS a host address - in other words, this netmask directly refers to the
host's complete address.
> So, you have a netmask of
>
> 11111111.11111111.11111111.11110000 255.255.255.240
>
> Therefore you have a host space of
>
> 00000000.00000000.00000000.00001111 0.0.0.15
>
> And its that simple, in a subnet with a mask of 255.255.255.240, you have
> 15 available addresses. BUT. Remever, with IP addressing the lowest
> address (all 0's in the host space) is the network address (identifies the
> subnet) and the highest address (all 1's in the host space) is the
> broadcast address. So you only really have 13 addresses that you can use
> for your actual hosts in the subnet.
You actually have 16 addresses in this range, with 14 useable. IP
numbering starts from ZERO - in other words, ZERO is a valid IP address -
so your range is from 0 to 15 - with 0 being the network address, and 15
being the broadcast address.
For example
IP Subnet Calculation & Design
-----------------------------------------------------------------------------
IP Class: C IP Address: 192.168.1.0
Mask Bits: 4 Subnet Mask: 255.255.255.240
Subnets: 14+1 IP Major Net: 192.168.1.0
Hosts/Subnet: 14 Major Net Bcast: 192.168.1.255
The list of subnets is as follows.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
No. Subnet Hosts Hosts Broadcast
Address From To Address
0 192.168.1.0 192.168.1.1 192.168.1.14 192.168.1.15
1 192.168.1.16 192.168.1.17 192.168.1.30 192.168.1.31
2 192.168.1.32 192.168.1.33 192.168.1.46 192.168.1.47
3 192.168.1.48 192.168.1.49 192.168.1.62 192.168.1.63
4 192.168.1.64 192.168.1.65 192.168.1.78 192.168.1.79
5 192.168.1.80 192.168.1.81 192.168.1.94 192.168.1.95
6 192.168.1.96 192.168.1.97 192.168.1.110 192.168.1.111
7 192.168.1.112 192.168.1.113 192.168.1.126 192.168.1.127
8 192.168.1.128 192.168.1.129 192.168.1.142 192.168.1.143
9 192.168.1.144 192.168.1.145 192.168.1.158 192.168.1.159
10 192.168.1.160 192.168.1.161 192.168.1.174 192.168.1.175
11 192.168.1.176 192.168.1.177 192.168.1.190 192.168.1.191
12 192.168.1.192 192.168.1.193 192.168.1.206 192.168.1.207
13 192.168.1.208 192.168.1.209 192.168.1.222 192.168.1.223
14 192.168.1.224 192.168.1.225 192.168.1.238 192.168.1.239
15 192.168.1.240 192.168.1.241 192.168.1.254 192.168.1.255
Note that you're not supposed to use subnet 0 {range 192.168.1.0 to
192.168.1.15} or subnet 15 {range 192.168.1.240 to 192.168.1.254} UNLESS
your routing device is fully conversant with more "advanced" routing. And
even then, I think the top subnet {number 15} is taboo - it breaks
broadcasting if you use it.
Also note that any form of subnetting wastes a certain number of IP
addresses - for "network" and "broadcast" addresses - and in this case,
22.83% of your IP addresses are wasted {I.E. cannot be used}, or 17.32% if
you use the bottom/top subnets.
DaZZa
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