Charles_Ragan @
ins .
com wrote:
>
> One other note, rfc 1878's recommendation allows for the usage of the first
> and last subnet. Routing protocols that carry subnet information in its
> updates allow for this. Ones that don't (igrp, static, ripv1, etc.). The
> practice I follow is to use them last, if needed.
>
> Charles
>
> At 01:55 AM 10/1/96 +2600, 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 > ___/ ___/
> >
> >
>
>
Sorry I forgot to mention it, but where I work we use OSPF which allows
variable subnetting and supernetting which the older protocols don't
support.
--
) _) Harry Feltsadas __
/ / mailto:harry @
fdc .
nl __ __(_ )
_ ) _ _/ http://www.fdc.nl/~harry ' | '/ /
__/ __/ __/ < A Red Goose, a Red Duck and a Red Daemon > ___/ ___/
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