Re: Public IP Address for Device behind Cable/DSL Modem

gabovitche@xxxxxxxxx wrote:
Need advice as to whether or not this is possible... We have several
ethernet building control devices that we want to connect to Cable/DSL
modems for internet access to their web pages and so they can
communicate with eachother. The catch is that each controller needs
to be configured with a static Public IP address and not a local IP
address. This is because each controller sends its static IP address
to the other controllers so they can talk to eachother on demand.

Will it be possible to arrange with ISP's to assign static Public IP
addresses to our building controllers, even though each controller
will be sitting behind Cable/DSL Modems?


What the hell is a "control device" or "controller"? Since their getting IP addresses, can we assume they're actually routers?

I can understand why they might need static IP addresses, but why would they need to be public IP addresses? If they're public IP addresses, not only can they communicate with each other, but everyone in the world can communicate with them, too. Also, with public IP addresses, the route between them will go back to the headend or central office for your ISP, where certain ports will be blocked preventing you from sharing files and printers.

I'm assuming this is a business, so you're likely to have greater security needs than a home user, so depending on NAT and the simple firewall features built into the typical home broadband router, you'll need to maintain three separate firewalls as well.

Essentially, the topology you're proposing is to set-up three separate networks, comparable to three neighbors on a street, each with their own home network. But even if you have static public IP addresses, you won't be able to communicate between the networks. In addition to the ISP blocking certain ports, you can run into some subnet issues as well.

Both cable and DSL providers can provide multiple IP addresses at an additional cost. Nearly all DSL providers, and many cable providers can also offer static IP address, but those usually come with business-level accounts. But I don't think getting multiple static public IP's is going to get you the results you are looking for.

Also, since these "control devices" have IP addresses, meaning they're likely actually routers, I have to wonder why? There might be some specific situation in which you want to essentially be running three separate networks in the same building, and still need them to act as a single network for some purposes, but that's a fairly advanced topology. It's far more likely that the "control devices" are actually hubs or switches, but in that case, they wouldn't even have IP address, let alone public IP addresses.

I'd suggest you contact your IT consultant to discuss exactly what it is that you have, and what you need to get the results you want. (And I know you can't be the IT guy because if you were, you wouldn't be talking about "controllers". You'd be using meaningful terminology.) I'm positive that whatever you actually need is entirely possible. What you're asking for now, however, will not accomplish even the very basic needs you're also communicating.

--
Warren H.

==========
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