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Airport Express Double NAT Bridge Mode Doesn't Work

A

Astral Cars

macrumors regular
Original poster
May 11, 2005
198
0
St. Paul
I was just trying to set up my Airport Express in my condo's new internet, provided by Access Media 3. I don't know much about the ISP, but when I got it set up it was telling me I have a "Double NAT" problem, so I switch to bridge mode and once I do that, the error goes away and it all looks good, except the internet doesn't work. My little airport menubar status shows the exclamation point in it. So should I just leave it with the "problem" or is there a different way I can resolve it that doesn't break my connection? Am I going to have additional problems by leaving it that way?
Thanks!
 
I have tried that with no success. It seems running it bridge mode makes it lose the internet, but I've got a double NAT otherwise.

Any other ideas?
 
Is your modem also a wireless router? What do you want the Airport Express to do?
 
I don't think it is, I just looked it up online and it says nothing of WiFi, just "cable modem". So I've connected the Airport Extreme to get some WiFi, and it's either in Bridge Mode with the internet not working, or not in Bridge Mode with internet working, but a Double NAT error.
Is this something that matters? Or should I just ignore the error and move on with my life?
 
Astral Cars said:
I was just trying to set up my Airport Express in my condo's new internet, provided by Access Media 3. I don't know much about the ISP, but when I got it set up it was telling me I have a "Double NAT" problem, so I switch to bridge mode and once I do that, the error goes away and it all looks good, except the internet doesn't work. My little airport menubar status shows the exclamation point in it. So should I just leave it with the "problem" or is there a different way I can resolve it that doesn't break my connection? Am I going to have additional problems by leaving it that way?
Thanks!
Click to expand...

Do you get a public IP address if you plug in your computer to the cable modem? (That is, *not* something starting something like 172.16-172.31, 192.168, or with a 10). If you get any of the latter, the problem is with the modem / provider.

I suspect that the modem is being a router of some kind.

It's possible they're giving you a private addressing system (and perhaps only giving you one - which prevents you using bridge mode), causing the double NAT.
 
Oh, sorry about the confusion there. It's just an Airport Extreme, don't know why I said Express earlier.

I plugged directly into the modem and got a public IP address (169.254.etc), but the internet didn't work. I restarted the modem, was given a generic 192.168.etc initially and after a few moments it switched to 10.128.etc. Now the internet works. So my problem is with the modem/provider then?
 
If you're plugging directly into the modem and your internet still doesn't work, yes, it is the modem. There are no other devices you can blame then.
 
Astral Cars said:
Oh, sorry about the confusion there. It's just an Airport Extreme, don't know why I said Express earlier.

I plugged directly into the modem and got a public IP address (169.254.etc), but the internet didn't work. I restarted the modem, was given a generic 192.168.etc initially and after a few moments it switched to 10.128.etc. Now the internet works. So my problem is with the modem/provider then?
Click to expand...

Ah, I see the problem.

So 169.254.0.0/16 addresses are what is called "link-local", basically they're self assigned IP addresses when there is no dhcp server to provide one, or when one hasn't been manually assigned. They don't allow for routing to the greater Internet.

Basically, your modem is locking to the first MAC (hardware) address it detects and will only give that device the IP address. You can't swap between your router, your computer etc without rebooting the modem first.

Hope that helps make sense of things.
 
I did get the modem to work directly connected to the computer. I just had to restart it first.

So if the modem is locking to the first device connected to it, I can just connect the Airport and it should work fine, but why the double NAT issue then? Are these "link-local" address a type of NAT so I get the error, but it's not actually problematic?
 
Yeah, I wonder if the Airport is seeing it as such. Did you see what IP address it was reporting in the Airport Utility?
 
Airport Utility shows an address of 10.128...
I guess I can just ignore the double NAT error, but it just makes me worry that it'll cause problems, especially as more devices are connected and the IP addressing gets more complicated.
 
So that 10.128 you're getting in both cases (direct or with the airport connected) is a private network address. When directly connected, your NAT'd once. The airport makes it two.

Do you have access to the modem configuration?

Few options:-

1) change the modem to (half-)bridge mode. Suspect this won't be possible though.
2) call your provider and ask why you aren't getting a public ip.

Basically this isn't anything to do with the Airport.

HTH
 
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