Michael J. McGillick <[EMAIL PROTECTED]> wrote:
>I'm setting up a NAT pool on a firewall.
Are the destination address on a separate network from the rest of your
internal network and that's why the subnetting is necessary or have I
missed something?
>I think I understand now that
>the netmask is independent of the starting address for the network it is
>masking. Just to make sure my understanding is correct, if my network
>starts at, say, 192.168.1.80, I can't very well have a netmask of anything
>smaller than 80, right? This would mean I was trying to set up an IP
>range large than 255.
Others have probably explained the netmask better than I can, but another
way to think about it: The netmask determines what portion of the IP
address is the network and what portion is the host. A class C IP address
of 192.168.1.80 with a subnet mask of 255.255.255.0 indicates that the
first 3 octets of the IP address are the network portion (192.168.1) and
the last octet (80) is the host. If we convert the dotted quad to binary
(each octet represents 8 zeros or ones), it is a little easier to see,
although I still trip over it quite frequently. (So someone tell me if
I've blown it again...)
11111111 11111111 11111111 <-network host-> 1010000
The first 3 octets are the network and the fourth is the host portion, so
we get a nice clean break and an easy to read subnet mask of 255.255.255.0
By setting the subnet mask to 255.255.255.248, we move the break between
the network & host portion like so:
11111111 11111111 11111111 11111 <-network host->000
which leaves us 32 networks, each having 6 usable IP addresses since the
first address is the network address and the last address is the
broadcast. As others have already pointed out, the closest you can get is:
192.168.1.80 subnet
192.168.1.81 first ip address
192.168.1.86 last ip address
255.255.255.248 subnet mask
But again, unless the NAT pool is on a separate physical network,
subnetting in this fashion may be unnecessary, unless I've missed something
obvious.
-Eric
Eric Sisler
Library Computer Technician
Westminster Public Library
Westminster, CO, USA
[EMAIL PROTECTED]
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