Local FTP

[David P. Schwartz]

I think I understand.  My DSL modem/router (Cisco 675) is running NAT as well.  All of my machines have "local" IPs assigned to them by the router's
internal DHCP server.  However, there's an EXTERNAL IP assigned (dynamically) to the other side of the cable modem.  If you look at the IP address of
this email, it says it came from something like 63.228.143.20.  But in fact the local IP address of the machine I'm on right now is 10.0.0.101 or
something like that.  (I could have used the 192.168.0.x format instead.)  This machine does not know any IP other than 10.0.0.101.

I actually have several machines hooked behind the router at the (temporary/dynamic) 63.228.143.20 IP, and one of them is running the DNS2GO client.
That machine's IP is actually assigned by the router as 10.0.0.102, but when the ping gets to the DNS2GO.com server, it sees it as 63.228.143.20.  Got
it?  (Try pinging digloo.d2g.com.  It doesn't show up as 10.0.0.102, does it?  However, it's getting routed from the DNS2GO server back to my router
based on the IP that shows up in the ping sent out by the machine running the DNS2GO client that identifies itself as 'digloo' and provides the
matching password.)

My understanding of things is that if the EXTERNAL IP of the router were indeed 168.192.0.x, (or even 10.0.0.x) then there would be no way for
anything to find its way down to the router from outside of it's "localized" subnet.

Now, in order for the DNS2GO client to work, my router had to be set up to route incoming traffic requests on port 80 (and other ports) to a static
local IP, in this case 10.0.0.102.  Otherwise NAT wouldn't know where to send the requests; and since there's no HTTP server listening inside the
router, they'd just get dropped.  (Maybe there's another way to do it, but this is what's working for me right now.)

The only way I can imagine what you're saying makes even a little sense is if the Cable America router is sitting in a switch box somewhere in the
neighborhood and each drop coming from the router to homes in the neighborhood is allocated a "local" IP from a DHCP server in the router.  Without
the ability to set up the static local IP mapping in the router's NAT, this could create a problem.  But then no requests would be able to get routed
back to your box; just replies.

Does this make sense, or am I totally confused about what you're saying?

-David

Troy wrote:

> The cable modem itself runs NAT
>
> Troy
>
> On Mon, 24 Dec 2001, David P. Schwartz wrote:
>
> > Then how do they allow for anything to get routed from their network down to your box???  I would imagine that would also make it impossible for
> > cookies to be left on the machine if the originating IP appears as a local-only address.  Which would prevent lots of e-commerce sites and
> > banking services from working.
> >
> > -David
> >
> > Troy wrote:
> >
> > > I think perhaps you missed what I was saying. :)
> > >
> > > Cable America gives you a local only IP.  ie.. 192.168.0.X style
> > > addressing unless you pay for a static IP which they bind to the MAC
> > > address of your NIC.  Obviously if you have a 192.168 address the rest of
> > > the internet cannot connect to it regardless of DNS service. =)
> > >
> > > Troy
> > >
> >