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    • CommentAuthorstarkeef
    • CommentTimeJul 22nd 2012
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    I am new to Open DNS and have a Surfboard 6121 Modem and an Airport Extreme running Airport Utility 6.1. I get my service through Comcast. Since I installed Open DNS my router changed from 'DHCP' Only to 'DHCP and NAT'. My internet works, but from time to time it will stop and I get the message 'Double NAT'. I have flushed the cache as recommended through Open DNS. But that doesn't seem to have solved the problem. Do I need to set the Router Mode to 'DHCP Only' or 'Off'?
  1.  permalink
    Turn off DHCP at the surfboard and give the Airport a static IP if it doesn't default to it's current one. Let the Airport be the DHCP server for the network.

    See this current post about what an Airport user did to set up the network:
    https://forums.opendns.com/comments.php?DiscussionID=15093&page=1#Item_5
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012
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    Okay, but I'm not sure how to turn off DHCP at the Surfboard 6121. I can get into the config area but it doesn't look as though there is any user configuration available. Maybe I just don't know where to look.
  2.  permalink
    Yeah, I certainly wouldn't know where to look, or if any options are available. When ISPs provide hardware, it almost never even has the options available on a non-re-branded standard version from the equipment vendor.

    Save yourself a headache if you aren't interested in trying to find something that likely isn't there, and just configure static DNS addresses on your computing device(s).
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012
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    Okay, I tried to set up my router via the settings I saw on the link you sent, but then got this message: "invalid value: The DHCP range you have entered conflicts with the WAN IP address of your base station'.
    Sorry, I may be a bit slow with the DHCP, NAT thing, but once I undderstand it, I'll know it forever. Thanks for your help.
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012
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    Here's another question: My SB6121 is acting as my router, correct? So, would the solution be to just let it do that and put my AE into Bridge Mode, when it will, I assume, work as just another wireless device and not fight with the modem?
    • CommentAuthorrotblitz
    • CommentTimeJul 23rd 2012 edited
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    What prevents you from just getting rid of the SB modem and use only the AE? Why would you need both at all?

    "invalid value: The DHCP range you have entered conflicts with the WAN IP address of your base station".

    What did you actually enter? What are the IP address of your router, the one of your computer, and what is the netmask?
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012 edited
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    So you are saying just go from the coax to the AE? I would have no idea how to do that. My setup is this: SB Modem> AE> Ethernet to house. The address of my router is 76.118.15.XXX Computer is:10.0.X.X
    • CommentAuthorrotblitz
    • CommentTimeJul 23rd 2012 edited
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    Well, if your ISP connection is coax, and your AE doesn't have a coax socket, then it is not possible to get rid of the SB. You didn't mention any of those details before.

    Further, if your setup is:
    ISP -- SB Modem -!- AE -- end user devices

    ...then your AE and possibly your SB have two IP addresses, a WAN facing and a LAN facing. Therefore the IP addresses you mention do not fully make sense.

    76.118.15.121 may be the WAN facing IP address of the SB, and 10.0.1.x is the IP address subnet on the LAN side of your AE. What are the LAN facing IP address of the SB and the WAN facing IP address of the AE? (This is the subnet part marked with -!-)

    This information would allow us to see if your SB acts as a router or just as a bridge.
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012
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    Sorry, I think this is a bit beyond me and I don't want to waste your time. I'll probably just go back to non-OpenDNS service until I can become a little more educated in this area.
    • CommentAuthorrotblitz
    • CommentTimeJul 23rd 2012
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    As you want, although you could have asked what you didn't understand.
    • CommentAuthorstarkeef
    • CommentTimeJul 23rd 2012
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    There was so much with modems and routers LAN facing WAN facing and how to find that stuff just got a bit overwhelming for me. I just reset my AE and we'll see how that goes.
    • CommentAuthorstarkeef
    • CommentTimeJul 25th 2012 edited
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    Okay, now that I've had a day to think about it, maybe you can help.
    When I look at the info for my AE it says IP address 76.118.15.XXX
    • CommentAuthorrotblitz
    • CommentTimeJul 26th 2012
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    Yes, it makes sense. Can you put the SB into bridge mode?
    • CommentAuthorstarkeef
    • CommentTimeJul 26th 2012
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    I tried that but every time I do it, it shuts down the internet connection at the modem. I have tried rebooting both the modem and AE after that and let it sit for a while, but the network doesn't come back, until I put the AE back to 'DHCP and NAT' mode. I am using the system to communicate right now, but it randomly will tell me that I have a 'Double NAT' and then disconnects.
    • CommentAuthorstarkeef
    • CommentTimeJul 26th 2012
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    I'm beginning to think that I need to return the SB6121 and get a Aris modem. The 6121 is obviously acting like a router and the two are trying to do the same job. I'll do some research and try to find a 'modem only' device that Comcast approves. I think this is a matter of an Apple compatibility issue. If anyone has a Motorola 6121 set up with an Aiport Extreme and it's working, please enlighten me. I would certainly appreciate any feedback.
    • CommentAuthorstarkeef
    • CommentTimeJul 26th 2012
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    Does anyone know if the Arris WBM760A would solve my problem? It has good reviews but if it also functions as a router, I'll have the same problem. I need a Comcast approved DOCSIS 3.0 device that is purely a 'dumb modem'.
    • CommentAuthorstarkeef
    • CommentTimeJul 27th 2012
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    So after all that, I went back to my SB5100. It's not DOCSIS 3.0 but it works like a charm. The SB 6121 is going back to Amazon. Thanks for your help.
    Thankful People: zelus
    • CommentAuthorrotblitz
    • CommentTimeJul 27th 2012
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    Ah, well done! Amazing!

This discussion has been inactive for longer than 30 days, and is thus closed.