I’ve seen you talk about NAT routers as firewalls, and so on. How do I know
if I have one?
The answer’s not as obvious as a lot of people are thinking. Yes, much of
the time a NAT router is an additional box … a device that you plug your
computer into that, in turn, plugs into your internet connection. And that box
will typically say “router” on it.
But that’s not the only way you can end up behind a router.
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As it turns out, many broadband modems also act as a router – and
they won’t say it on the outside. Knowing whether they’re acting as a NAT
router is important – you might be able to avoid buying an extra router you
don’t actually need, or you might be able to avoid installing firewall software
you don’t actually need.
Finding out is fairly simple.
My favorite way is to open a Command Prompt – that’s
usually done this way:
Click on Start
Click on All Programs
Click on Accessories
Click on Command Prompt
You’ll probably get window similar to this one:
In that Window type “ipconfig” followed by the enter key, and you should get
something like this:
Now, like me, you may have more than one network adapter. The one you
probably want to pay attention to is the one labeled Local Area
Connection, for wired connections, or Wireless Network
Connection if you’re running via a WiFi or other wireless
The line you care about is this one:
"font-family: 'Courier New', Courier, monospace; font-size: larger;">IP
Address. . . . . . . . . . . . : 192.168.1.2
That’s your computer’s IP address. If it begins with “192.168”, as mine
does, then you are almost certainly behind a NAT router. IP addresses that
begin with “192.168” are actually invalid on the internet as they are
specifically intended for non-internet, local networks. The router performs
what’s called “Network Address Translation”, or NAT, to translate from your
local IP address to your internet IP address as assigned by your ISP.
You may also see an IP address beginning with “10.”, or some addresses
beginning with “172.” – these, too, may mean that you are behind a router of
some sort, but these are typically NOT used by modems and consumer-grade
routers. They’re typically used for larger installations such as corporations,
hotels or some ISPs.
So if your computer is connected directly to your broadband modem, and you
have a “192.168.” address, then your modem is acting as a NAT router. If you
have some other address, then it’s not, and you probably want to investigate
installing a NAT router or firewall.