>First of all, thanks to all those who responded.
Just to clarify, you are talking about discontiguous subnet masks
here, which is not the same as discontiguous networks. A
discontiguous network exists when pieces of the same major network
(i.e., from a classful standpoint) are separated by a different
network:
Address 10.1.0.0 ------- 192.168.0.0 --------10.2.0.0
Mask 255.255.0.0 255.255.255.0 255.255.0.0
>
>The last octet mask is three bit but .148 which is 1001 0100.
>
>My curiosity was aroused when during our class discussion of subnetting, our
>instructor (I just don't know if I heard it correctly) mentioned that the
>bits (for the subnet) can be anywhere in the octet. We were discussing the 3
>bit mask which is .224.
Your instructor is completely wrong. See RFC 1812, which clears up
earlier ambiguous specification and flatly says subnet masks must be
contiguous. Even if earlier RFCs did not prohibit it, the RFC
process does not go back and change earlier ones, but issues new
versions.
Yes, there may be implementations here and there that support
discontiguous masks. But discontiguous masks break the classless
addressing rules by which the Internet runs.
>
>So it the subnet bits can be located anywhere in the octet (although our
>instructor mentioned not to waste our time on this as Cisco does not support
>this kind of subnet masks), I made up a different mask for the 3 bit which
>in this case is 148 (1001 0100).
>
>So, what now? For a three bit mask, there would be 6 usable subnets (I am
>excluding subnet zero). My problem now is, what is my 1st subnet and what
>are the hosts for this subnet. And what are the other subnets (and their
>corresponding hosts)?
So it's really not very helpful to talk about discontiguous masks,
because they won't be used by any standards-compliant implementation.
>
>It made my head spin and kept me awake. So, this is the reason why I asked
>the list.
>
>Until this time, it keeps me thinking.
>
>Arthur
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