I'm just a bit curios so I'll reply.
ishAdmin wrote:I'm keeping this in layman's terms since I'll say the wrong thing if I start discussing classes and subnets. I've never cracked a book on that topic, and only have experience managing little class C subnets.
There's not really any big differences except for ease of subnetting. The basics are still the same so I want to try to figure out what you're experiencing.
ishAdmin wrote:Here, with a computer connected directly to the dsl modem, we get whatever IP we are assigned (with dhcp, or static (if we pay more)). And it's the same as the internet IP. We are directly connected to the net, each of us with a unique IP.
It's very similar here: I've got a dsl "modem/router/box" (it neither modulates/demodulates nor routes anything so both those names make me go bonkers lol
rather it's just like a powered bridge with NAT).
Anyway the dsl lan output can go either directly to a pc using a normal ethernet cable or one can use a crossover ethernet cable from the dsl to any kind of hub/switch/router as neccesary (one needs to cross the wirepairs inside the cable in relation to the plug which is why the cable is named crossover, this is because the ports on both devices are of the same physical configuration). If you have a router with a cascade port or similar you wont need a crossover cable but those are usually only found on "real" routers who often get daisychained.
My current setup is that the dsl lan side connects to a small powered switch.
ishAdmin wrote:With some ISP's, we can pay extra for extra internet IP's. If they allow this, then all we need is a hub or switch connect to our dsl modem so we can have more than one computer. Each computer would dhcp it's own internet IP. Or we could even have our own static IP for each computer if we pay extra.
Ok here is where I find things get a bit weird. First of all: any ISP is willing to sell you additional ip's but usually with it's own line, and any ISP will charge extra for static addresses. It can definetly be as you say with some ISP's but that rests on one fact alone: wheter or not they are giving you dsl connection devices/"routers" with NetworkAdressTranslation (NAT). If they give out dsl "routers" without it then it surprises me a lot because almost every kind has support for NAT (as well as DHCP) built into them. I've seen *dsl connection devices without NAT but they're extremely rare and afaik they stopped making any without NAT many years ago as it's so cheap to include (close to zero cost) while making it so much more useful.
Anyway the question becomes this: does your dsl "router" have NAT or not? If it has NAT then you can do the same as me and countless others and the ISP can't say anything about it legally: it's none of their business. If you don't have NAT then you need the solution you are using now.
This got a bit long but I just want you to find out for yourself as if you have NAT then it saves you a lot of trouble that's all. DHCP is easy to run as a local service on your main pc so that's not really necessary (but DHCP is just about as usual to have included as NAT). NAT does not require a static ip.
One last question: when you connect to or ping the *dsl box you have from your computer what ip-address do you use? Or in other words: when you configure your tcp/ip what ip do you use as gateway address (this would usually be the *dsl box). Since you use a pc (or another router?) as an internal gateway you have to look there and see which ip it uses for the *dsl device. If that address is 10.0.0.1 or 172.16.0.1 or 192.168.0.1 I can guarantee you that you have NAT on the *dsl box.
Btw here are the ranges reserved for free lan use (within each lan):
A class 10.0.0.0 through 10.255.255.255
B class 172.16.0.0 through 172.31.0.0
C class 192.168.0.0 through 192.168.255.0