Re: public/private IPs and subnet masks

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John Wunderlich wrote:
=?Utf-8?B?YmlmZg==?= <biff@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:F494FE8A-FE02-4013-805A-D213BA428B5B@xxxxxxxxxxxxx:

biff wrote:
Say you have a computer on IP 132.132.132.6 with subnet mask
255.255.255.0 and gateway 132.132.132.254

You want to setup your new network printer with a private IP. The printer gets a private IP of 10.78.22.130. What do you put
into the printer for a subnet mask? Do you put 255.255.255.0? What would you put for the gateway on the printer since it is a
private IP but you want it to communicate with your public IP
computer?

Are all the computers and printer on the same network, using the
same switches? If so, are you just trying to "hide" the printer
from the other computers on the network? If the latter is true
you should use 132.132.132.254 for the gateway on the printer. Of course this does not prevent others from using the printer if
they find the address and set up their computer to access that
printer.

Thanks for the post Michael. Yes all the printers and computers
are on the same network although there are a couple of subnets on
the network. The printers are private to conceal their presence.

I wonder if it matters which subnet gateway the printer should get
once the printer is assigned a private IP?

"Michael W. Ryder" wrote:


In order for this to work, the NIC on your computer must have two IP addresses assigned to it -- one on the 132.132.132.x subnet and one on the 10.78.22.x subnet. The 132.x.x.x address will give your computer connectivity to your local network and router, and the 10.x.x.x address will provide connectivity to your printer.

Windows does allow more than one IP address to be assigned to a NIC but only when DHCP is disabled. So to do this, you will have to go to the Network control panel for your NIC, then:
Properties-> Scoll down & Double-click on "TCP/IP" in the window ->
Click "Use the following IP address" and manually set up your IP Address in the 132.x.x.x subnet. It goes without saying that you should avoid any IP addresses "owned" by a DHCP server. After that, click "Advanced" button and in the "IP Address" window, click "Add" and enter an additional address for your computer in the 10.x.x.x subnet. This will configure your computer.

The printer configuration subnet mask should match the subnet match you configured on your computer above for the 10.x.x.x subnet and both computer & printer must be in the same logical subnet. The gateway setting on your printer does not matter because there is no gateway on your 10.x.x.x subnet that it can use -- IOW, the printer can only be accessed by computers in the same physical subnet and thus a gateway setting is moot (such is the nature of private addresses).

FWIW: While this will work, it is Mickey-Mouse at best and a down-
right nuisance if your computers ever need DHCP.

HTH,
John

Are you sure about this? I print all the time to a printer on a different subnet 75 miles away without having to set up two IP addresses. The computer and printer need to know how to get to the other subnet but that is handled by the gateway.
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