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  1. #1


    Member Since
    Mar 07, 2009
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    15
    Airport Problem: Double NAT
    So I've read the other posts with this issue, most seem to ignore it and it still works, I haven't done anything and my internet works fine, but does anyone know what the problem really is and what is the best thing to fix it.

    My air port has 2 options for me, I attached a screen shot of it.

    My airport is hooked up to my cable modem which automatically provides the IP and DNS addresses. My internet seems to work fine with this problem, should I ignore it or chose one of the options?
    Attached Images Attached Images

  2. #2

    dtravis7's Avatar
    Member Since
    Jan 04, 2005
    Location
    Modesto, Ca.
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    28,930
    Specs:
    iMac 2010 27" QuadI7 OSX10.11, iMac 2008 OSX10.11, MBP Late2011OSX10.11 , iPad Air, iPhone 3GS
    What is the brand and model of your cable modem?

  3. #3


    Member Since
    Mar 07, 2009
    Posts
    15
    I'm not too sure, it was given to me by my ISP and there wasn't a name or anything major on it, on the underneath of the modem I found the model # and a name Ambit on some sticker with the FCC logo on it. The model # is u10c018. Don't know if that helps.

  4. #4

    Collin Bl's Avatar
    Member Since
    Apr 07, 2009
    Location
    Napier NZ
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    Specs:
    27 iMac i5, MBP 13 & iMac 20, 2TB dual TC, AppleTV, iPh4S
    My limited understanding is that you have a deal that is redundant. You have an address that is being handed out and then handed out again because the airport is set to hand out DHCP instead of being bridged. The drama will occur when you have more units on your LAN and incoming data can't find it's way to the correct MAC - as in Machine Address Code - It does work but change the airport to Bridge, what is the problem with doing that?

  5. #5


    Member Since
    Apr 07, 2008
    Posts
    187
    Hi,
    I have a similar configuration as you:

    Code:
    public IP ROUTER 192.168.1.1/24 ---- AirPort Express --- wlan --- my Macs
    I'd recommend that you use the Bridge mode. In this case, the AirPort will just relay all the network communication into the wlan and your macs/pc will be in the same network as the router (e.g. 192.168.1.1)

    If you use the "double NAT", your mac/pc would be in a new network as follows



    Code:
    public IP ROUTER 192.168.1.1/24 ---- AirPort Express 10.2.0.0/24 --- wlan --- my Macs
    It's called double NAT because if you wanted to open a port for an application, you'd need to redirect (NAT) the port two times:
    - on your router to the Airport Express
    - on your Airport Express to your mac

    So if you don't have a special need where you want to have two different networks, I'd go for the bdridged mode.

    hope it helps

    Tex

  6. #6


    Member Since
    Mar 28, 2009
    Posts
    45
    I would hazard a guess that your cable modem is also a router. Does it have multiple CAT5 ports on the back? If so, then it more than likely is and is already pushing out IP's via DHCP. I'm also basing my assumption on the fact that your airport is getting a private IP vs. a public IP that a regular cable modem would normally assign to the computer that's attached to it.

    All that to say, I would recommend bridged mode.

  7. #7


    Member Since
    Apr 07, 2008
    Posts
    187
    Quote Originally Posted by twdcmd View Post
    I would hazard a guess that your cable modem is also a router. Does it have multiple CAT5 ports on the back? If so, then it more than likely is and is already pushing out IP's via DHCP. I'm also basing my assumption on the fact that your airport is getting a private IP vs. a public IP that a regular cable modem would normally assign to the computer that's attached to it.

    All that to say, I would recommend bridged mode.
    Yes right, my previous post will only work only if your modem is also a router but I also suppose that it is a case

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