DNS - which modem/router/OS has priority?

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I Plan to Stick Around
Posts: 16

DNS - which modem/router/OS has priority?

Maybe this does not belong in a Rogers forum and if so, let me know and I accept that.

 

There are three places I know of to enter DNS servers in my setup:

  • Rogers modem - Hilton CGN3
  • My router - ASUS RT-N66U
  • In my Operating System (OS) network settings - I use Linux Mint but Windows would be the same I assume.

 

 

If CGN3 is not bridged (is in gateway mode) with no router ... easy ... the DNS servers in there are used.

 

If I bridge CGN3 and set my ASUS router to control DNS settings to some OpenNIC DNS servers ... I assume (hope) they would be used. I can not tell as my OS reports only one DNS server ... 192.168.1.1 (very bottom of code below) ... I know that is not really what they are but I have no idea what is used for sure.

IPv4 Settings:
    Address:         192.168.1.189
    Prefix:          24 (255.255.255.0)
    Gateway:         192.168.1.1

    DNS:             192.168.1.1

 

If I leave the ASUS router above 'as is' with my custom DNS servers in there .... BUT if I enter the same DNS servers into my OS network settings ... and run the same tool to ask what are my DNS servers ... its reports them as what I entered as seen below:

IPv4 Settings:
    Address:         192.168.1.189
    Prefix:          24 (255.255.255.0)
    Gateway:         192.168.1.1

    DNS:             198.xxx.xxx.xxx
    DNS:             208.xxx.xxx.xxx

 

This is confusing to me as I don't know what really has priority to control my DNS servers. I will guess that my ASUS router would trump the Rogers modem ... and then my OS would trump both of those? Can anyone tell me. Kinda like ... the closer to home is the BOSS?

 

I got onto this because when trying to find fastest DNS servers using namebench or the one from GRC (Steve Gibson I think), they would not test my DNS servers in my router as tthey were reported as 192.168.1.1

 

 

***edited labels***

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Resident Expert
Resident Expert
Posts: 6,104

Re: DNS - which modem/router/OS has priority?

I do believe that your OS DNS servers have priority.  I run mine through the CGN3 but I'm looking at reinstalling DNSCrypt to encrypt DNS data.  If you do a search in Windows Help and Support for "Change TCP/IP settings" and follow the settings instructions you will see that selecting the DNS source in the OS will over-ride the router feed for DNS addressing.

 

The other consideration is that by placing your DNS address on your pc and laptop, even if your router is ever hacked, and the DNS address is changed, you still have control over what address source is actually used, which in this case is within the PC or laptop.  A key consideration in the event of hacking.

 

I'm not sure what happens when you have two routers in line followed by the pc, but from what I remember, there should be a selection on the second router to obtain the DNS source from the default gateway.  Say for example you had the CGN3 in gateway mode followed by the N66U, followed by the PC or laptop.  If the selection for using the default gateway DNS wasn't checked in the second router (N66U), then the DNS addressed would come from that second router.  If you then decided to use the address within the OS, then any DNS address in either router should be ignored.

 

I've used Steve Gibson's benchmark tool before and from the site page comes the following:  

 

When the Benchmark is started in its default configuration, it identifies all DNS nameservers the user's system is currently configured to use and adds them to its built-in list of publicly available “alternative” nameservers. 

 

So, in order to rank your current DNS nameserver, you would have to set it to a legitimate server address, either in the routers or in the OS. 



I Plan to Stick Around
Posts: 16

Re: DNS - which modem/router/OS has priority?

Great info for a few reasons. I will add the DNS servers in all my OS from now on. Actually for some reason, with my OS reporting my DNS servers were actually my gateway ... both benchmark programs would not include my DNS servers. I could add them manually but I didn't know if they were valid. Now, they will pick them up.

 

 I love that info on DNS hacking ... wow new one on me. I see some options on geting DNSCrypt working in Linux so I will give that a go. Thanks for that!

 

BTW ... when I did the benchmarks ... I did manually add the primary Rogers DNS server and I was surprised it came out on top in one of them... but I don't want to use them.

 

ps I don't know why but I x'd out my DNS servers in original post. You got me a lil DNSnervous Smiley Surprised