Am I behind my ISP's NAT?

Question

I have a router and 2 computers connected to it.

When I go to one of those "Check My IP" websites the ip it shows is 74.236.***.** (I have starred out the last part of the ip just in case posting your ip is not allowed here, or something).

When I go to the command prompt and type in ipconfig it shows:

IP Address. . . . . . . . . . . . : 192.168.75.40
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.75.1

I use that 192.168.75.1 address to access my router's web interface. I go to the status page of the router settings. It shows this:

Internet IP Address: 192.168.1.97

On my old ISP, it would show:

Internet IP Address: 24.blah.blah.blah

y'know, like a normal ip address beginning with 24. And it would be identical to the ip address that would come up on those "Check My IP" websites.

But with my new ISP it's not like that. My router is set up just like before with the old ISP

So you see there are 4 ip's here:

My computer: 192.168.75.40
My router's internal ip: 192.168.75.1
The address that my modem assigns to my router: 192.168.1.97
The external ip that is picked up by websites:74.236.***.**

After a little searching I figured out how to access the modem's settings and I put it on IP passthrough, hooray! :)

Answer 1

Well, it appears you are indeed behind a NAT in front of your router. Many MODEMS these days are set that way. I know AT&T uses some speedstreams with NAT in them. Its just another level of protection for the users. In many cases you can log into the modem and turn OFF the routing by using bridge mode. (You really are running two routers at this point.)

But if its working, and you can't run servers anyway, what difference is there? Just means you are harder for bad guys to crack!

Answer 2

I agree with the first poster. You are behind a NAT.

I had a Verizon DSL connection a while ago and they used a Westell DSL router that acted as a NAT device. I was able to log into that device and configure it to forward a few ports inbound. On these ports I was able to run a server. You can check to see if such an option works on your DSL router (192.168.75.1).