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I have configured my DGN2200v2 to do the following:

  • Reserve the LAN address for my mac to 10.0.0.11
  • Use 10.0.0.11 as primary DNS server, and 8.8.8.8 as secondary

Now I would expect the router to ask my computer for DNS requests, but it seems to just skip the 10.0.0.11 server and uses 8.8.8.8...(I checked using Wireshark and my computer isn't getting any requests, and the pages load so I guess that's what's happening)

Is there something I am missing here? I have checked using ipconfig and I indeed have the IP of 10.0.0.11.

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  • You have a DNS server configured on your desktop? If you do, set the forwarder to a public DNS so the request can go somewhere. Can you ping 10.0.0.11 from your router?
    – Citizen
    May 28, 2016 at 2:21
  • @Citizen for some reason there's 100% packet loss... prntscr.com/b9drhg I checked using wireshark, and this is what's going on: prntscr.com/b9dry4
    – Amit Gold
    May 28, 2016 at 8:30
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    Well, by default Windows have firewall enabled and will block ping (and others)...
    – Tom Yan
    Jun 1, 2016 at 17:54
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    @VojtěchDohnal How does it not make sense? I want my router to forward DNS requests to a computer on the network instead of the ones that my ISP tells it to or 8.8.8.8, and then my computer might return some junk IP or might ask 8.8.8.8. Right now I can use nslookup with server as 10.0.0.11 and it works and the server logs the action, but when asking 10.0.0.138 which is supposed to in turn forward to 10.0.0.11, the server doesn't log anything and the requests don't get filtered...
    – Amit Gold
    Jun 6, 2016 at 16:08
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    @VojtěchDohnal to clarify, I am doing both nslookups from another device which is connected to the same router.
    – Amit Gold
    Jun 6, 2016 at 16:08

2 Answers 2

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+50

Reserve the LAN address for my mac to 10.0.0.11. So you did something like this:

enter image description here

It is not really relevant to your issue though. Anyway, you can certainly ping this address from your PC:

enter image description here

(I actually wonder if an OS would even route it to your router when it can easily recognize this is its own address)

However, with your Windows Firewall on, you won't be able to ping from your router to your PC:

enter image description here

Once your have configured it properly, or have it disabled (for testing), it will ping fine:

enter image description here

Use 10.0.0.11 as primary DNS server, and 8.8.8.8 as secondary; I am not sure how exactly you did that, but certainly, you can configure on the client side statically:

enter image description here

Or through the LAN-side DHCP server setting:

enter image description here

But certainly, first of all you need to have a DNS server built up on your PC:

enter image description here

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  • So basically my testing is bad I guess, I will try actually making a query from another computer and see if it works. I am not at home right now though so expect updates :D
    – Amit Gold
    Jun 5, 2016 at 16:57
  • @AmitGold Btw, beware of bad DHCP server implementation on some routers...
    – Tom Yan
    Jun 6, 2016 at 15:10
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I think there is a misconception here : DNS queries are not part of the router services - all the router does is only to communicate the IPs of the two specified DNS servers to your computer, and it is your computer that issues the DNS queries.

So what happens is that your computer tries to forward DNS queries to itself, but unfortunately by using its external IP address, which means that the connection is done through the router. A connection of this type usually cannot work except via the loopback interface on IP 127.0.0.1 (localhost), which does not pass through the router.

Most consumer-grade routers do not support loopback, which is a computer addressing itself via the router. Such a router will either protect itself against the risk of looping eternally in a circular manner, or its firmware will simply not have the code required to keep track of loopback connections.

The end-result is that the DNS server at address 10.0.0.11 is quickly marked as unusable by your computer when it boots, or on the first DNS query, so is probably already being ignored when you launch Wireshark.

Conclusion : The router is working properly for a consumer-grade router.

Remark :

In general, it is not useful to have two DNS servers, one primary and the other secondary, since Windows will only use one. The secondary DNS server is the backup in case that the first one fails. You will need to define these DNS servers on your computer, not on the router, but Windows will only use the first that answers.

The local DNS server must be defined by the IP address of 127.0.0.1 (localhost). If a local DNS server is to be used by Windows, then this server needs to know how to fall back to the Google server at 8.8.8.8 if it cannot find an answer locally, because Windows will not do this automatically.

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  • That sounds correct to me. How are you making these dns requests? If the requests are coming from the same computer, that's a loop. The router shouldn't need to make dns queries unless it's for a completely different thing. If there are other devices that need dns, I would think they should be pointing to the dns server directly. If your router is advertising dhcp, the internal dns should be what is advertized.
    – BloodyEl
    Jun 1, 2016 at 21:40
  • It seems to me what you want to do should be doable, with the exception of the "consumer-grade" part. If you have hardware lying around you could also just use a linux box as a router and firewall without it costing anything and without proprietary compromises.
    – BloodyEl
    Jun 1, 2016 at 21:44
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    AFAIK it's only common that a "consumer-grade" router does not support being addressed from the LAN with its WAN side IP address (port forwarded or not). I have never seen "loopback issue" as what you've described.
    – Tom Yan
    Jun 4, 2016 at 3:40
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    So you are trying to say that when he writes ping 10.0.0.11 on his PC, it will fail because of his router? Never seen this too.
    – Vojtěch Dohnal
    Jun 6, 2016 at 11:29
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    @VojtěchDohnal: Yes, I thought this was clear from my answer. If you think it's unclear, feel free to add to it. Although this is not only a security feature - the router needs to be able to keep track of it and a simple router will not have the code for it.
    – harrymc
    Jun 7, 2016 at 10:08

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