Harry Feltsadas wrote:
>
> 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 __
> / / mailto:harry @
fdc .
nl __ __(_ )
> _ ) _ _/ http://www.fdc.nl/~harry ' | '/ /
> __/ __/ __/ < A Red Goose and a Red Duck > ___/ ___/
In http://cio.cisco.com/warp/public/701/3.html, All 0's or 1's in
network part can't be used.
So if you subnet C class with 255.255.255.192, the number of effective
network is 2 I think.
In default network, We can't use 0 and 255 number as network number.
For example for A class, the first byte of IP address can't be 0 or 255.
So if you subnet C class with 255.255.255.192 (use 2 bits), 00 and 11
can't be used for subnetting bits.
References:
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