On Mon, 17 Jul 2000, Dean Hamstead wrote:
> > 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.
>
> when you use a subnet like 255.255.255.240 which 14 address's can be
> used?
> with 255.255.255.0 is all 255 in the last byte, eg 192.168.0.x
>
> with 255.255.255.240 is it the last 14 address's?
> can i use it to take a chunk from the middle?
> eg. 192.168.0.15 - 30?
The short answer is - yes.
The long answer is - with caveats.
Generally, when using private addressing, subnetting is a waste of time
unless you've got
1) Multiple sites or
2) Extremely complex networking
Subnetting is only really useful for public networking which connects to
the net - and even then, you need pretty specialised circumstances to use
it.
Basically, with a .240 subnet mask, for every 16 IP addresses, you can use
the middle 14 - in other words, you can do this
IP range Useable addresses
----------------------------------------
0-15 1-14
16-31 17-30
32-47 33-46
48-63 49-62
You get the idea. However, you have to be logical - you can't just take a
chunk here, and a chunk there - if you _really_ need 14 node segments,
then take then from the early part of the subnet range, and make them
contiguous - don't use, say, the 0-15 range for one segment, then say the
112-127 range for the next - because _ALL_ the unused addresses between .0
and .127 are wasted unless you apply similar 14 host networks in this
range {or another multiple which will fit - a 30 host network in the 64-95
range, maybe}. Basically, non contiguous networks are wasteful of
addresses - subnet masking is wasteful of addresses - anything except the
base class netmask is wasteful of addreses. :-)
Unless you have a specific reason for subnetting this far, don't do it -
all it does is make your router work harder, and unless your network is
over 50 or 60 nodes [per physical segment], you're wasting your time.
DaZZa
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