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Thread: DNS not working after Upgrade to 12.04

  1. #11
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by magis3xludi View Post
    I think that the query to the loopback interface is the result of the line
    Code:
    dns=dnsmasq
    in the NetworkManager.conf file
    If "dns=dnsmasq" is there then NetworkManager starts a dnsmasq process which listens for DNS queries on 127.0.1.1 (formerly 127.0.0.1, in Precise); NetworkManager also sees to it that "nameserver 127.0.1.1" appears in resolv.conf.

    If you comment out "dns=dnsmasq" and "sudo restart network-manager" then no such dnsmasq process will be started.

    but if I delete this line what will happen if I connect by the router (I have to connect to two different adsl line but I have only one router so I want to use a modem on one of them)?
    Feel free to comment out "dns=dnsmasq". If you have resolvconf installed then everything should still work. Without "dns=dnsmasq" NetworkManager will put upstream nameserver addresses directly in resolv.conf instead of giving them to the dnsmasq process.

    If you use NetworkManager for one interface it's best to use it for all interfaces. Otherwise it's best to use it for no interfaces and use ifupdown + /etc/network/interfaces instead.

    Having said that, it may be possible to configure one interface with NetworkManager and another interface with ifup or pon or whatever. But keep in mind that NetworkManager controls the default route.

  2. #12
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by jdthood View Post
    If you use NetworkManager for one interface it's best to use it for all interfaces. Otherwise it's best to use it for no interfaces and use ifupdown + /etc/network/interfaces instead.
    I tried using NetworkManager also for the dsl connection but it seems that it can't manage it because doesn't see the interface (perhaps because is an usb modem?). When I create with the connection scripts in the linked guide 2 interfaces, nas0 and ppp0, I copied their MAC addresses onto the DSL connection described in Networkmanager but again it doesn't notice the activity of these 2 interfaces. Then I have to use pon and poff for the ppp connection but I will be happy if I could use NetworkManager also for the ppp connection because it's the simplest way to manage connections I think.
    But your hint is precious anyway, I can't figure why changing manually /etc/resolv.conf have no effect, I did not know at all what the dnsmasq process does, I'll disable it and all should be working then.But there is any real advantage of using dnsmasq?I haven't ever changed this option then I think it is a default of the system.
    Thanks a lot, best regards
    Last edited by magis3xludi; December 10th, 2012 at 12:50 PM. Reason: another question that I forgot

  3. #13
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by magis3xludi View Post
    I tried using NetworkManager also for the dsl connection but it seems that it can't manage it because doesn't see the interface (perhaps because is an usb modem?).
    Hundreds of bug reports have been filed against network-manager reporting faulty support for modems. Very few modems are officially supported. See https://live.gnome.org/NetworkManager/MobileBroadband.

    I did not know at all what the dnsmasq process does, I'll disable it and all should be working then.
    Disabling the NetworkManager-controlled dnsmasq process will at least make debugging easier.

    But there is any real advantage of using dnsmasq?
    You have to distinguish between standalone dnsmasq as included in the "dnsmasq" and "dnsmasq-base" packages, and NetworkManager-controlled dnsmasq as included in the "network-manager" and "dnsmasq-base" packages. Dnsmasq per se has many features: it is a DHCP server and a caching forwarding nameserver. All these features are available if you install "dnsmasq", but that package is not installed by default. Only "network-manager" and "dnsmasq-base" are installed by default in Ubuntu Desktop. NetworkManager uses Dnsmasq *only* as a forwarding nameserver (not even caching). The way this is done can in theory improve performance in VPN environments but in practice it has caused many malfunctions. Fortunately the NetworkManager-controlled dnsmasq process can be disabled.

  4. #14
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by jdthood View Post
    Disabling the NetworkManager-controlled dnsmasq process will at least make debugging easier.
    I would know how to debug it, before
    I disabled dnsmasq commenting the line in NetworkManager.conf, logged out and rebooted-> no way to surf with the modem and also with the router, perhaps I have to set DNS on NetworkManager because without dnsmasq the system doesn't receive the dns from the router?
    Then I re-enabled dnsmasq and I am able to surf if I connect my pc to the router.
    I noticed that the dnsmasq process start when an interface managed by NetworkManager is up. Before I connect to the router by my wifi usb dongle if I start the ppp connection using the usb adsl modem a request to dns is managed in this way
    Code:
    sudo more /etc/resolv.conf
    nameserver 85.37.17.8
    nameserver 85.38.28.73
    maurizio@XubuDesktop:~$ host -d google.it 85.37.17.8
    Trying "google.it"
    Using domain server:
    Name: 85.37.17.8
    Address: 85.37.17.8#53
    Aliases: 
    
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31393
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
    
    ;; QUESTION SECTION:
    ;google.it.         IN   A
    
    ;; ANSWER SECTION:
    google.it.      117   IN   A   173.194.35.184
    google.it.      117   IN   A   173.194.35.191
    google.it.      117   IN   A   173.194.35.183
    
    Received 75 bytes from 85.37.17.8#53 in 58 ms
    Trying "google.it"
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18991
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
    
    ;; QUESTION SECTION:
    ;google.it.         IN   AAAA
    
    ;; ANSWER SECTION:
    google.it.      288   IN   AAAA   2a00:1450:4016:801::1017
    
    Received 55 bytes from 85.37.17.8#53 in 58 ms
    Trying "google.it"
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43461
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
    
    ;; QUESTION SECTION:
    ;google.it.         IN   MX
    
    ;; ANSWER SECTION:
    google.it.      524   IN   MX   30 alt2.aspmx.l.google.com.
    google.it.      524   IN   MX   40 alt3.aspmx.l.google.com.
    google.it.      524   IN   MX   50 alt4.aspmx.l.google.com.
    google.it.      524   IN   MX   10 aspmx.l.google.com.
    google.it.      524   IN   MX   20 alt1.aspmx.l.google.com.
    
    Received 145 bytes from 85.37.17.8#53 in 60 ms
    maurizio@XubuDesktop:~$ host -d google.it
    Trying "google.it"
    ;; connection timed out; no servers could be reached
    Then if I specify the same server that is listed as primary in /etc/resolv.conf the dns query is performed, if I do not specify server the query can't be performed and the system doesn't try to reach the server listed. The process dnsmasq is not running till I start wi-fi connection to the router so is not in charge for this strange behaviour

  5. #15
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    Re: DNS not working after Upgrade to 12.04

    I disabled dnsmasq commenting the line in NetworkManager.conf, logged out and rebooted-> no way to surf with the modem and also with the router
    It appears that you don't have resolvconf installed, or that resolvconf is installed but /etc/resolv.conf is not a symbolic link to ../run/resolvconf/resolv.conf. Consequently resolv.conf is not getting updated properly.

    If you disabled NetworkManager-controlled dnsmasq (by commenting out "dns=dnsmasq" in /etc/NM/NM.conf) and this caused name resolution to stop working entirely then probably you had "nameserver 127.0.1.1" in a static /etc/resolv.conf file.

    Later it seems you ran pppd and it wrote some addresses to /etc/resolv.conf but these were only valid when used over the PPP connection. But I am not sure.

    You should purge and reinstall resolvconf, reboot, and then either use NetworkManager to manage all your network connections or use ifup/ifdown to manage them all.

  6. #16
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    Dec 2012
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    Re: DNS not working after Upgrade to 12.04

    It appears that you don't have resolvconf installed, or that resolvconf is installed but /etc/resolv.conf is not a symbolic link to ../run/resolvconf/resolv.conf. Consequently resolv.conf is not getting updated properly.
    Yes, that's true. In the guide I followed for installing the speedtouch modem with pppoe connection they say that the symlink has to point /etc/ppp/resolv.conf.
    I reconfigured resolvconf and now I'm writing connected by the modem
    Thanks a lot,finally I have my connection up!
    regards

  7. #17
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by magis3xludi View Post
    In the guide I followed for installing the speedtouch modem with pppoe connection they say that the symlink has to point /etc/ppp/resolv.conf.
    I edited that guide to say that in Ubuntu 12.04 and later the admin shouldn't touch /etc/resolv.conf. In Ubuntu 12.04 and later, which have the resolvconf utility installed by default, resolvconf takes care of updating resolv.conf when nameserver addresses are received (by pppd, in this case).

    That guide is out of date in other ways. For example, the br2684ctl program can now be installed with apt-get and doesn't have to be downloaded from a website. I changed this part too, but someone should go through the whole document and bring it up to date.
    Last edited by jdthood; December 12th, 2012 at 06:47 AM.

  8. #18
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    Re: DNS not working after Upgrade to 12.04

    Hi Everyone!

    I am having similar problem. I installed DNS server long ago using this article
    http://www.danbishop.org/2011/10/29/...-dhcp-and-dns/

    And it has been working perfectly, last night I upgraded my OS and pufff my network goes down. I checked
    /etc/network/interfaces
    /etc/resolv.conf
    /etc/dnsmasq.conf

    It looks the same as before.
    Internet works fine on the server computer and I am able to ping other computers in the network and other computers can ping the server. But Internet is not working on other computers.

    I don't know what went wrong, if anyone knows anything please post... much appreciated.

    - Saket Kumar
    http://saketkumar.com

  9. #19
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    Re: DNS not working after Upgrade to 12.04

    Quote Originally Posted by saketkumar View Post
    I am having similar problem.
    Your problem is not similar to the one the opened this thread:
    I cannot access my ISP's DNS when using a static IP. Internet incoming and outgoing is still unaffected.
    Please start a new thread saying that you have one machine that can connect to the Internet, other machines that can't, and this time describe the topology of the LAN, the machines that are on it and the software installed on those machines. Also describe how you expect networking to function on your LAN.

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