Two easy networking questions

Question

I have basic understanding of networking, but I just want to know to more thing I don´t understand.

So, I have 1st Router, which is connected to DSL/Router and than internet. So my structure is this:

PC -> (LAN port) Router (WAN port) -> (LAN port) DSL/Router (WAN port) -> Internet

So, if I may, my first question is: If I connect Router to DSL/router in way I would use LAN port on Router instead of WAN port, would I still be able to connect to internet? I think the real question is, when you send ip request to Router, and its not one of its internal IP adresses, does it resend that request on WAN and LAN ports, OR WAN only?

And the second question is, DSL/Router´s LAN ip pool is from 10.0.0.1 network. The Router IP pool is from 192.168.0.1 network (I am really sorry I forgott its class name, I belive first is A and second is C thou). So, I CAN connect from PC to DSL/Router. But I thought I cannot, becouse I want to access internal IP adress, and I though these adresses are NOT routed. o I assumed its gonna be discarded by Router. Why?

I hope I explained it clearly. thanks for any answers.

Answer 1

The Internet functions with multiple layers of routers as a matter of course. For example, when your traffic leaves your house and travels over the DSL, it hits a carrier router, and likely several others before getting to its final destination. The Windows tracert command can show you all the intermediate hops that your traffic takes between your PC and the final destination. Your main issue will be NAT, however.

Almost all consumer grade routers support getting their "WAN" address via DHCP. And, almost all consumer grade routers have built-in DHCP servers, and will hand out a range of addresses of your choosing on your LAN ports. If you want to chain multiple routers in this fashion, by having one router get an address via DHCP from another, it will work.

Your routers are also performing a function called NAT. This is necessary because most consumer grade Internet connections will only get a single IP from their ISP. NAT actually rewrites traffic back and forth on the fly, allowing multiple machines behind the router to share and appear from the outside as though they are all from a single IP address. Since you are using two routers, you are going to be "double-NATed." This is only an issue if you want run server-type software that accepts incoming connections without initiating outgoing connections.

So, let's say Router A gets its WAN IP from your ISP, and hands out addresses on its LAN ports in 10.0.0.0/24 (that's 10.0.0.1 through 10.0.0.254). You have a server connected to the LAN ports of Router A. It has address 10.0.0.3 and the server software is listening on port 2000. You need to configure port forwarding in Router A to forward incoming traffic on port 2000 to 10.0.0.3. This is where DHCP sucks, because what if your DHCP lease expires and your router gives a different IP. But it won't change the port forwarding configuration. So I would configure Router A DHCP to give out addresses in the range 10.0.0.1 through 10.0.0.127, and manually assign 10.0.0.129 to the server. That way it will always be accessible no matter what DHCP does.

Now, throw Router B in the mix. Router B gets its WAN IP from router A, and is set to hand out addresses on its LAN ports in 192.168.0.0/24 (that's 192.168.0.1 through 192.168.0.254). You have a server connected to the LAN ports of Router B. The port forwarding of Router B must match with Router A otherwise your traffic will get to the 10.0.0.0/24 LAN but never your 192.168.0.0/24 LAN. And you can see why it'd be better to give Router B an IP manually instead of relying on DHCP, because if DHCP suddenly decides to give Router B a different IP you'd have to reconfigure your port forwarding.

I hope this is helpful.

Answer 2

For the kind of network you're looking at, a better layout would be:

[PC] -> [Router1: LAN-port -> Router1: LAN-port] -> [Router2: LAN-port -> Router2: WAN-port] -> Internet.

Or put another way, the first router connects to the internet-connected router with a lan-port to lan-port connection. The reason for this is that you don't need a second subnet for the other router (in most at-home situations, anyway) so just treat the first router like a switch and not a router.

Setting it up this way means you're at much less risk of doing a double-NAT traversal which can break all kinds of things. You only get one NAT translation, on the Internet connected router, which makes things work normally.

You'll get a single subnet in this case, from the sounds of it it'll be 10.0.0.0/24. This will make talking to all of your internal devices a lot easier.