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Author Topic: DNS Servers  (Read 20391 times)

Golfer

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DNS Servers
« on: April 25, 2012, 03:24:25 PM »

Hi All - I trust this is the right area for my queries, please feel free to move it if not!

I've recently changed ISP to Virgin Media (all well and good - 30Mb soon to be 60Mb) and have their Superhub.  I've also ditched Windows Vista and am running Linux Mint 12.  On Vista, (ISP then was TalkTalk) my DNS server varied between Open DNS and Google.  Now, with Virgin, their own DNS server is apparently 'locked into' the hub firmware and can't be changed? 

Query 1 - is this so or is there a workaround?

Various web searches (including Virgin's site) say to configure the settings directly into my computer and this I've done -  (they appear in the config box as correct) and have followed the 'how to' instructions very carefully.  When I access the OpenDNS test page, however, the site says I'm not set up for their service! 

Query 2 - how does this software actually work?  Does the computer determine the path or the router?  And if the settings are actually 'locked' into the hub, do they override the computer's settings?

It seems that Virgin are under a lot of pressure to enable the changing of DNS servers on Superhub but it doesn't look like there will be a resolution anytime soon.  I would much prefer to use a non-ISP DNS server if possible.  Any pointers would be a great help - I'm very new to Linux, by the way, so words of one syllable would be appreciated!

Thanks in advance

Rich



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roseway

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Re: DNS Servers
« Reply #1 on: April 25, 2012, 03:35:48 PM »

If you configure your computer to access your preferred DNS servers directly, the system should respect that, and DNS requests will be passed straight through the router. However, have you confirmed that the configuration changes you made in the computer have actually stuck? The reason I ask is that the DNS subsystem in Debian (and presumably Debian-based distros) changed a little while back. Previously you could edit /etc/resolvconf directly, but now if you do that it gets overwritten on the first reboot. So you have to make the change elsewhere, and I'm not sure how Mint arranges this.
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Golfer

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Re: DNS Servers
« Reply #2 on: April 26, 2012, 08:35:54 PM »

If you configure your computer to access your preferred DNS servers directly, the system should respect that, and DNS requests will be passed straight through the router. However, have you confirmed that the configuration changes you made in the computer have actually stuck? The reason I ask is that the DNS subsystem in Debian (and presumably Debian-based distros) changed a little while back. Previously you could edit /etc/resolvconf directly, but now if you do that it gets overwritten on the first reboot. So you have to make the change elsewhere, and I'm not sure how Mint arranges this.

Hi Eric and thanks for the reply.

I'd hoped that it was the case as per the first part of your answer.  The second part though is proving difficult.  I've tried several methods as outlined in various forums around the net, both by configuring 'network connections' directly and through terminal.  The settings are there (and remain so after re-boot) but when I use terminal to check them, the router settings are listed 1st and 2nd and OpenDNS 3rd and 4th in the list.  Try as I might, I can't figure out how to edit the settings in terminal to move them up!  More research is required, obviously................  ;D



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Blackeagle

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Re: DNS Servers
« Reply #3 on: April 27, 2012, 10:30:46 PM »

Dunno much about Linux, but, on a windows box, one would remove the DNS resolver pointing at the router.

EG, if your router is at 192.168.0.1 then generally your DNS server address would be the same as the gateway (192.168.0.1) and the router would hand on DNS queries to the resolvers it picked up from the ISP.  If however you remove that address from the DNS resolver list and add a different one, say 8.8.8.8 for google DNS, then the PC will never ask the router for a DNS query, it will instead query google DNS directly, in spite of the fact that the router has picked up the ISP's DNS settings.

As I understand it, if you edit the /etc/resolv.conf file manually then if you are using NetworkManager it will be overwritten on each boot.

This link may help.
« Last Edit: April 28, 2012, 12:17:31 AM by Blackeagle »
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burakkucat

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Re: DNS Servers
« Reply #4 on: April 27, 2012, 11:17:15 PM »

Blackeagle -- Someone has typed a malformed link! I wonder who it was?  ::)
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Blackeagle

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Re: DNS Servers
« Reply #5 on: April 28, 2012, 12:20:33 AM »

Blackeagle -- Someone has typed a malformed link! I wonder who it was?  ::)

Oooops  :-[

Sorry, the other forum I frequent has slightly different code for the formatting of URL's.  I haz repaired it now b*cat. I'm sure your *nix experience would be most welcome here  :)
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asbokid

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Re: DNS Servers
« Reply #6 on: April 28, 2012, 12:54:20 AM »

I've not used Mint, but it's Debian-based.   Linux Mint probably has the same NetworkManager applet as Debian..



The Virgin Superhub presumably assigns both an IP address to your PC(s) and nameserver addresses.   This will be done using the DHCP protocol.

NetworkManager can be configured to obtain an IP address for the PC, but also to use hard-coded IP addresses for the nameservers.


cheers, a




« Last Edit: May 02, 2012, 02:06:15 AM by asbokid »
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burakkucat

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Re: DNS Servers
« Reply #7 on: April 28, 2012, 01:03:06 AM »

Oooops  :-[

<snip> I haz repaired it now b*cat. I'm sure your *nix experience would be most welcome here  :)

I may not actually click on a link but I'll always hover the cursor over it, just to see to which address it vectors.

Thanks for the prompt fix!  :thumbs:
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pintosal

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Re: DNS Servers
« Reply #8 on: April 28, 2012, 01:46:25 PM »

Another option is to run your own DNS using the free Treewalk DNS software - good for Windows, and works for me.
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Golfer

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Re: DNS Servers
« Reply #9 on: April 30, 2012, 09:58:01 AM »

Hi asbokid - thanks for that.

I do configure the network as per your screenshot and the settings remain in place after reconnect/reboot etc. However, when I access the Opendns website to test the connection, I get the Oops! message and clicking their other links shows I'm not on their service!  Frankly, I'm stumped.............

Rich
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geep

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Re: DNS Servers
« Reply #10 on: April 30, 2012, 12:18:24 PM »

Hi,
On my Slackware Linux the contents of /etc/resolv.conf list the nameserver(s).
It is refreshed at every boot.
By default mine contains:
Code: [Select]
# Generated by dhcpcd from eth0
# /etc/resolv.conf.head can replace this line
nameserver 192.168.1.254
# /etc/resolv.conf.tail can replace this line

So my default nameserver is my router @ 192.168.1.254

Just to confuse - I actually modify my /etc/resolv.conf at boot using rc.local.
I update it with other nameservers in a priority order, so that it ends up with:
Code: [Select]
# Generated by dhcpcd from eth0
# /etc/resolv.conf.head can replace this line
search lan
nameserver 127.0.0.1
nameserver 94.30.127.100
nameserver 89.145.254.78
nameserver 192.168.1.254
# /etc/resolv.conf.tail can replace this line

I'm running dnsmasq locally - also started up via rc.local, so I have a local cacheing nameserver on localhost 127.0.0.1 (if my memory serves me correctly - it was setup ages ago).
I have
Code: [Select]
dnsmasq -o start in my rc.local to start my local nameserver after updating the resolv.conf

References (lots more on similar topic if you Google...):
http://www.cyberciti.biz/tips/how-do-i-improve-dns-performance-on-linuxwindows-desktop.html
http://www.debianadmin.com/local-dns-cache-for-faster-browsing-on-ubuntu-system.html

Although I did this setup on Linux, I ran a benchnark using this tool:
http://www.grc.com/dns/benchmark.htm
running on a Windows Virtual Machine. I could see that after the first access to a URL, subsequent accesses were indeed faster.
The cache of dnsmasq is refreshed at every boot.

dig is an interesting tool for looking at dns performance.
Here's an example of the cacheing in operation when I went to povray.org:
This is the first visit to povray.org today - dns lookup pretty slow:
Quote
dig povray.org   

; <<>> DiG 9.7.4-P1 <<>> povray.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4507
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;; QUESTION SECTION:
;povray.org.                    IN      A

;; ANSWER SECTION:
povray.org.             3600    IN      A       203.29.75.48

;; AUTHORITY SECTION:
povray.org.             414     IN      NS      ns1.povray.org.
povray.org.             414     IN      NS      ns1.aussie.org.

;; Query time: 2099 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Apr 30 12:06:46 2012
;; MSG SIZE  rcvd: 87

On subsequent visits to povray.org - dns lookup is instant thanks to the cache:
Quote
dig povray.org

; <<>> DiG 9.7.4-P1 <<>> povray.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15118
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;povray.org.                    IN      A

;; ANSWER SECTION:
povray.org.             3596    IN      A       203.29.75.48

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Mon Apr 30 12:06:50 2012
;; MSG SIZE  rcvd: 44

Oh, and welcome to Linux...

Cheers,
Peter





« Last Edit: April 30, 2012, 12:21:30 PM by geep »
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asbokid

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Re: DNS Servers
« Reply #11 on: May 02, 2012, 02:05:05 AM »

Hi asbokid - thanks for that.

I do configure the network as per your screenshot and the settings remain in place after reconnect/reboot etc. However, when I access the Opendns website to test the connection, I get the Oops! message and clicking their other links shows I'm not on their service!  Frankly, I'm stumped.............

Rich

What is the contents of your /etc/resolve.conf file?  Sometimes it is just a symlink to another file..

Maybe run netstat in one console window, and then ping anyoldsillysitename.com from another window..

Code: [Select]
$ ping hubblelkdfjsddskfjsddfg.com
ping: unknown host hubblelkdfjsddskfjsddfg.com

And from the other console we can see the udp/53 connection to the nameserver with IP address 8.8.8.8 (as configured in /etc/resolv.conf)..

Code: [Select]
$ sudo netstat -nucp
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
udp        0      0 192.168.1.2:60078       8.8.8.8:53              ESTABLISHED 10899/ping     

cheers, a
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Golfer

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Re: DNS Servers
« Reply #12 on: May 02, 2012, 11:36:56 AM »

This reply to peter and asbokid - thanks again for your help

When I try to open   /etc/resolve.conf in Terminal I get this, which suggests my system might not be configured correctly -

~ $ /etc/resolve.conf
bash: /etc/resolve.conf: No such file or directory
richard@xxxxxxxxx ~ $ sudo /etc/resolve.conf
[sudo] password for richard:
sudo: /etc/resolve.conf: command not found

Trying the other commands either produce a similar result or a string of data I don't comprehend!  I don't fully understand what it is I'm doing or looking for (in my defense I'm a very new newbie! :baby:).  Does this mean that certain files are missing and I should install them - if so, where from and how?

Can you recommend a good, basic beginners guide to using Terminal?
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asbokid

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Re: DNS Servers
« Reply #13 on: May 02, 2012, 02:27:54 PM »

This reply to peter and asbokid - thanks again for your help

When I try to open   /etc/resolve.conf in Terminal I get this, which suggests my system might not be configured correctly -

~ $ /etc/resolve.conf
bash: /etc/resolve.conf: No such file or directory
richard@xxxxxxxxx ~ $ sudo /etc/resolve.conf
[sudo] password for richard:
sudo: /etc/resolve.conf: command not found

My bad!  It's /etc/resolv.conf (no 'e' on the end). It's just a text file rather than a program to run, so load it with a text editor (e.g. gedit)

Code: [Select]
$ gedit /etc/resolv.conf

Quote
Can you recommend a good, basic beginners guide to using Terminal?

The terminal is called the 'shell'.. There are loads of shells to choose from in Linux/Unix. The most popular shell is called the bash shell, or the "Bourne Again SHell".

The first thing you notice is how much more powerful bash is than the poor old command.com shell that Microsoft ships with Windows.

Fairly complex programs called 'shell scripts' are written to run in Unix shells.  There are some programmers who are employed solely to write Unix shell scripts!

The official bash manual is here [1]  There are other bash manuals: the Bash Guide for Beginners from Machtelt Garrels looks good. [2]

cheers, a

[1] http://www.gnu.org/software/bash/manual/
[2] http://writers.fultus.com/garrels/ebooks/Machtelt_Garrels_Bash_Guide_for_Beginners_2nd_Ed.pdf
« Last Edit: May 02, 2012, 07:42:50 PM by asbokid »
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Golfer

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Re: DNS Servers
« Reply #14 on: May 02, 2012, 08:49:26 PM »

My bad!  It's /etc/resolv.conf (no 'e' on the end). It's just a text file rather than a program to run, so load it with a text editor (e.g. gedit)

My eyesight!  I didn't pick up the correct spelling in your screenshot!

I edited and saved resolv.conf then restarted but on checking it had placed the router DNS addresses above mine in the list.  Thus -

nameserver 127.0.0.1
nameserver 194.168.4.100
nameserver 194.168.8.100
nameserver 208.67.222.222
nameserver 208.67.220.220

The 1st line seems correct, the 2nd and 3rd are the Virgin nameservers.  The final 2 are opendns, which is what I want.

Peter's reply in the post below yours is beyond me at this stage - sorry Peter!   :no:  I'll don my student cap and have a thorough read-up in the links you posted.  Don't go away.....................

Thanks again

Rich

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