SG Broadband Community

Well, I've never heard "borrow from" when talking about subnetting. I assumed that you meant "borrow bits from the host addresses".

For example: a Class C has 24 bits of mask (11111111.11111111.11111111.00000000 or 255.255.255.0), leaving 8 bits (the "0" or "don't care" bits) for host addresses ...

I'm always hesitant to download files from someone I don't know - it's a good way to get hammered by a virus. You might want to provide a less-risky and convoluted way to see the topology. Perhaps just a clear description?

I'm trying to migrate web servers from DSL (routed) to Cable (bridged). I configured NAT on an identical Cisco router in the same manner as the one connecting us to DSL for the past ten years. Ethernet comes out of the cable modem and goes into the new Cisco; Ethernet comes out the Cisco's other ...

There are a couple of short articles at TechRepublic.com that may help. Links tend to change over time, so I'll give you the title:
Cisco IP subnetting 101: Five things you should know
The section titled
What do 1s and 0s have to do with it
tells you adding 1s to the end of the subnet mask ...