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Thread: DNS problems

  1. #1
    Join Date
    May 2008
    Location
    New Zealand
    Beans
    28
    Distro
    Ubuntu 10.04 Lucid Lynx

    DNS problems

    I have a problem with internet connectivity. I am a complete newbie :-) there is another person in the house who has had a crack at this and posted a thread with no joy (http://ubuntuforums.org/showthread.php?t=839166) I need a patient person to give me a simple step by step approach to tackling this. I can use terminal and have a basic understanding of how things work, but not much idea of how the networking set up really works.

    I noticed the issue a day or so ago, the machine had been running for several days and Firefox open and running fine during that time. Then out of the blue, no other applications could access the net. There were some updates during that period but apart from that I can't see what might have triggered this. No new software installed that I can think of. After a reboot, Firefox could no longer connect normally.

    It is an AMD64x2 box running ubuntu 8.04. Its networked (wired D-Link router which has been rebooted) with this laptop on XP and another box running Xbuntu. The other machines have no connectivity issues.

    I can ping the other machines no problem, I can ping by IP but not by name. Firefox konqueror or wget will connect to sites using IP address (depending on the site - at least google) but not by name. We can resolve an address with nslookup or dig, ipv4 or ipv6

    We have changed the DNS server settings in Network manager (using applet) to the openDNS servers 208.67.222.222
    208.67.220.220, to no effect.

    From what I've read on similar problems, here's some hopefully relevant info:

    Code:
    $ ifconfig 
    
    eth0      Link encap:Ethernet  HWaddr 00:1d:7d:93:32:e9  
              inet addr:10.1.1.4  Bcast:10.255.255.255  Mask:255.0.0.0 
              inet6 addr: fe80::21d:7dff:fe93:32e9/64 Scope:Link 
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1 
              RX packets:894 errors:0 dropped:0 overruns:0 frame:0 
              TX packets:5582 errors:0 dropped:0 overruns:0 carrier:0 
              collisions:0 txqueuelen:1000 
              RX bytes:119501 (116.7 KB)  TX bytes:539627 (526.9 KB) 
              Interrupt:23 Base address:0x2000 
    
    lo        Link encap:Local Loopback  
              inet addr:127.0.0.1  Mask:255.0.0.0 
              inet6 addr: ::1/128 Scope:Host 
              UP LOOPBACK RUNNING  MTU:16436  Metric:1 
              RX packets:1605 errors:0 dropped:0 overruns:0 frame:0 
              TX packets:1605 errors:0 dropped:0 overruns:0 carrier:0 
              collisions:0 txqueuelen:0 
              RX bytes:112121 (109.4 KB)  TX bytes:112121 (109.4 KB)
    Code:
    $ cat /etc/network/interfaces 
    
    # This file describes the network interfaces available on your system 
    # and how to activate them. For more information, see interfaces(5). 
    
    # The loopback network interface 
    auto lo 
    iface lo inet loopback 
    
    # The primary network interface 
    auto eth0 
    #iface eth0 inet dhcp 
    
    iface eth0 inet static 
    address 10.1.1.4 
    netmask 255.0.0.0 
    gateway 10.1.1.1
    Code:
    $ route -n 
    
    Kernel IP routing table 
    Destination     Gateway         Genmask         Flags Metric Ref    Use Iface 
    169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0 
    10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0 eth0 
    0.0.0.0         10.1.1.1        0.0.0.0         UG    100    0        0 eth0
    Code:
    $ cat /etc/resolv.conf 
    nameserver 208.67.222.222 
    nameserver 208.67.220.220 
    nameserver 10.1.1.1
    Code:
    $ sudo iptables -L -vnx 
    [sudo] password for rob: 
    Chain INPUT (policy DROP 0 packets, 0 bytes) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 ACCEPT     tcp  --  *      *       208.67.222.222       0.0.0.0/0           tcp flags:!0x17/0x02 
         109     7703 ACCEPT     udp  --  *      *       208.67.222.222       0.0.0.0/0           
           0        0 ACCEPT     tcp  --  *      *       208.67.220.220       0.0.0.0/0           tcp flags:!0x17/0x02 
           0        0 ACCEPT     udp  --  *      *       208.67.220.220       0.0.0.0/0           
          25     2220 ACCEPT     tcp  --  *      *       10.1.1.1             0.0.0.0/0           tcp flags:!0x17/0x02 
           0        0 ACCEPT     udp  --  *      *       10.1.1.1             0.0.0.0/0           
        1605   112121 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
           0        0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 10/sec burst 5 
           0        0 DROP       all  --  eth0   *       0.0.0.0/0            255.255.255.255     
        5845   499482 DROP       all  --  *      *       0.0.0.0/0            10.255.255.255      
           0        0 DROP       all  --  *      *       224.0.0.0/8          0.0.0.0/0           
           0        0 DROP       all  --  *      *       0.0.0.0/0            224.0.0.0/8         
           0        0 DROP       all  --  *      *       255.255.255.255      0.0.0.0/0           
           0        0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0             
           0        0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID 
           0        0 LSI        all  -f  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 10/min burst 5 
          42    32182 INBOUND    all  --  eth0   *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG_FILTER  all  --  *      *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           LOG flags 0 level 6 prefix `Unknown Input' 
    
    Chain FORWARD (policy DROP 0 packets, 0 bytes) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 10/sec burst 5 
           0        0 LOG_FILTER  all  --  *      *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           LOG flags 0 level 6 prefix `Unknown Forward' 
    
    Chain OUTPUT (policy DROP 1 packets, 140 bytes) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 ACCEPT     tcp  --  *      *       10.1.1.4             208.67.222.222      tcp dpt:53 
         109     7217 ACCEPT     udp  --  *      *       10.1.1.4             208.67.222.222      udp dpt:53 
           0        0 ACCEPT     tcp  --  *      *       10.1.1.4             208.67.220.220      tcp dpt:53 
           0        0 ACCEPT     udp  --  *      *       10.1.1.4             208.67.220.220      udp dpt:53 
           0        0 ACCEPT     tcp  --  *      *       10.1.1.4             10.1.1.1            tcp dpt:53 
           0        0 ACCEPT     udp  --  *      *       10.1.1.4             10.1.1.1            udp dpt:53 
        1605   112121 ACCEPT     all  --  *      lo      0.0.0.0/0            0.0.0.0/0           
           0        0 DROP       all  --  *      *       224.0.0.0/8          0.0.0.0/0           
          35     3209 DROP       all  --  *      *       0.0.0.0/0            224.0.0.0/8         
           0        0 DROP       all  --  *      *       255.255.255.255      0.0.0.0/0           
           0        0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0             
           0        0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           state INVALID 
        5492   455646 OUTBOUND   all  --  *      eth0    0.0.0.0/0            0.0.0.0/0           
           0        0 LOG_FILTER  all  --  *      *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           LOG flags 0 level 6 prefix `Unknown Output' 
    
    Chain INBOUND (1 references) 
        pkts      bytes target     prot opt in     out     source               destination         
          42    32182 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
           0        0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
           0        0 ACCEPT     all  --  *      *       10.1.1.2             0.0.0.0/0           
           0        0 ACCEPT     all  --  *      *       10.1.1.4             0.0.0.0/0           
           0        0 LSI        all  --  *      *       0.0.0.0/0            0.0.0.0/0           
    
    Chain LOG_FILTER (5 references) 
        pkts      bytes target     prot opt in     out     source               destination         
    
    Chain LSI (2 references) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 LOG_FILTER  all  --  *      *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x17/0x02 limit: avg 1/sec burst 5 LOG flags 0 level 6 prefix `Inbound ' 
           0        0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x17/0x02 
           0        0 LOG        tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x17/0x04 limit: avg 1/sec burst 5 LOG flags 0 level 6 prefix `Inbound ' 
           0        0 DROP       tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp flags:0x17/0x04 
           0        0 LOG        icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 limit: avg 1/sec burst 5 LOG flags 0 level 6 prefix `Inbound ' 
           0        0 DROP       icmp --  *      *       0.0.0.0/0            0.0.0.0/0           icmp type 8 
           0        0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/sec burst 5 LOG flags 0 level 6 prefix `Inbound ' 
           0        0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0           
    
    Chain LSO (0 references) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 LOG_FILTER  all  --  *      *       0.0.0.0/0            0.0.0.0/0           
           0        0 LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0           limit: avg 5/sec burst 5 LOG flags 0 level 6 prefix `Outbound ' 
           0        0 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-port-unreachable 
    
    Chain OUTBOUND (1 references) 
        pkts      bytes target     prot opt in     out     source               destination         
           0        0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           
          65     7184 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
           0        0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           state RELATED,ESTABLISHED 
        5427   448462 ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0
    Would really appreciate some help with this. Pretty much stuck in the mud here :-)

  2. #2
    Join Date
    Mar 2006
    Location
    Kitakyushu Japan
    Beans
    9,361
    Distro
    Ubuntu 11.04 Natty Narwhal

    Re: DNS problems

    have you tried rebooting the router? sounds basic, but it could fix this problem.

  3. #3
    Join Date
    May 2008
    Location
    New Zealand
    Beans
    28
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: DNS problems

    Quote Originally Posted by dmizer View Post
    have you tried rebooting the router? sounds basic, but it could fix this problem.
    Hi and thanks for the quick reply.
    Yep, I've tried rebooting the router, no joy.

  4. #4
    Join Date
    Mar 2006
    Location
    Kitakyushu Japan
    Beans
    9,361
    Distro
    Ubuntu 11.04 Natty Narwhal

    Re: DNS problems

    only other thing i can suggest trying would be to disable ipv6.

    just add
    Code:
    blacklist ipv6
    to /etc/modprobe.d/blacklist

    reboot and test. if you are able to browse after that, then you may have a problem with how your router handles ipv6 addressing. if this does not fix the problem, just remove the "blacklist ipv6" line from /etc/modprobe.d/blacklist and reboot.

  5. #5
    Join Date
    May 2008
    Location
    New Zealand
    Beans
    28
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: DNS problems

    only other thing i can suggest trying would be to disable ipv6.
    OK, did that - no change :-(

  6. #6
    Join Date
    Mar 2006
    Location
    Kitakyushu Japan
    Beans
    9,361
    Distro
    Ubuntu 11.04 Natty Narwhal

    Re: DNS problems

    do you have a spare router? is there a firmware update available for your router? are you running third party firmware?

  7. #7
    Join Date
    Sep 2006
    Location
    Solihull/Piraeus (UK/GR)
    Beans
    421
    Distro
    Ubuntu 11.10 Oneiric Ocelot

    Re: DNS problems

    Check also this file:

    Code:
    cat /etc/nsswitch.conf
    I'm not exactly a networking expert, but iptables seems to show packets being exchanged via udp in both directions with the OpenDNS server 208.67.222.222 on port 53, which is precisely as expected, so I guess the problem must lie somewhere after the reply is received.

    What exactly do you get if you do:

    Code:
    nslookup ubuntu.com

  8. #8
    Join Date
    May 2008
    Location
    New Zealand
    Beans
    28
    Distro
    Ubuntu 10.04 Lucid Lynx

    Re: DNS problems

    Think I may have another router will have a look shortly and give a whirl. Seem to be locked out of the current router at the moment. Will need to check password with the other user when he arrives.

    Other info -

    Code:
    $ cat /etc/nsswitch.conf 
    # /etc/nsswitch.conf 
    # 
    # Example configuration of GNU Name Service Switch functionality. 
    # If you have the `glibc-doc-reference' and `info' packages installed, try: 
    # `info libc "Name Service Switch"' for information about this file. 
    
    passwd:         compat 
    group:          compat 
    shadow:         compat 
    
    hosts:          files mdns4_minimal wins [NOTFOUND=return] dns mdns4 
    networks:       files 
    
    protocols:      db files 
    services:       db files 
    ethers:         db files 
    rpc:            db files 
    
    netgroup:       nis

    Code:
    ~$ nslookup ubuntu.com 
    Server:		208.67.222.222 
    Address:	208.67.222.222#53 
    
    Non-authoritative answer: 
    Name:	ubuntu.com 
    Address: 91.189.94.249
    thanks for your help on this :-)

  9. #9
    Join Date
    Sep 2006
    Location
    Solihull/Piraeus (UK/GR)
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    421
    Distro
    Ubuntu 11.10 Oneiric Ocelot

    Re: DNS problems

    Quote Originally Posted by rothbert View Post
    We can resolve an address with nslookup or dig, ipv4 or ipv6
    OK, I missed that bit on first reading So, DNS is not the problem.

    Just as an experiment, try moving dns higher up the order in nsswitch.conf:

    Code:
    hosts:          files dns mdns4_minimal wins [NOTFOUND=return] mdns4

  10. #10
    Join Date
    Mar 2006
    Location
    Kitakyushu Japan
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    9,361
    Distro
    Ubuntu 11.04 Natty Narwhal

    Re: DNS problems

    Quote Originally Posted by wdaniels View Post
    OK, I missed that bit on first reading So, DNS is not the problem.

    Just as an experiment, try moving dns higher up the order in nsswitch.conf:

    Code:
    hosts:          files dns mdns4_minimal wins [NOTFOUND=return] mdns4
    if you do this, then you will break local name resolution. i assume you have winbind installed?

    this really looks like a router problem.
    Last edited by dmizer; June 26th, 2008 at 08:28 AM.

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