John McColley @ J F Engineering wrote:
>
> Let's see if I understand subnetting correctly.
> If I want to split a class C network to setup a firewall I would
> take the existing network, say a.b.c.0 with a netmask of
> 255.255.255.0 and instead I would end up with 2 usable networks
> if I use a netmask of 255.255.255.192. I would end up with
> network a.b.c.64 with a netmask of 255.255.255.192 and network
> a.b.c.128 with a netmask of 255.255.255.192. Therefore, I would
> have available addresses of a.b.c.65 (netmask 255.255.255.192)
> through a.b.c.126, broadcast address would be a.b.c.127 and
> a.b.c.129 (netmask 255.255.255.192) through a.b.c.191, broadcast
> address would be a.b.c.192.
> I can't use a.b.c.0 through a.b.c.63 and a.b.c.193 through
> a.b.c.255.
> Does this sound right?
>
More or less. Subnetting uses a subnet mask. Any bit that is on in
the mask is a network bit. If the bit in the mask is off, the
bit belongs to a host part of the address. In your case above,
using a mask of 192 means that the first two bits are the subnet,
the rest are hosts. The first two bits give 4 networks (not two).
So in this case, you can use all four!
If you want two subnets, use a different subnet mask, and remember,
the net bit can be anywhere, so you can divide it into two parts,
as long as it's a power of two. This way, you don't lose that
many numbers!
--
) _) Harry Feltsadas __
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