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Thread: dns lookup not working

  1. #1

    Default dns lookup not working

    Yesterday I upgraded openSUSE from 11.0 to 11.1, after finishing upgrade, dns lookup are not working. Direct connection using IPs works fine, and logging in with skype also works, but not anything else.

    I'v read this: [opensuse] dns resolution problems - fresh 11.1rc1 install
    wich looks like my problem, except I got the finished 11.1

  2. #2

    Default Re: dns lookup not working

    i updated 11.0 to 11.1RC1 a while back and had some similar experience. Update and no network, i enabled the ifup traditional setup and disabled the checkbox for ipv6 in yast2/NetworkDevices/GlobalOptions. This workaround got me going again and i haven't gone back to figure out exactly why.

    hope it helps.

  3. #3

    Default Re: dns lookup not working

    I too have been suffering with _horrible_ network issues, all which
    appear to be DNS related, since my 11.1 installation. I have six
    machines in my home office; all six are on the same network, using the
    same router. Only one machine is running openSUSE 11.1. ALL five other
    machines are having _no_ network issues. The openSUSE 11.1 machine
    isn't even usable due to the network "host unreachable" errors. Its
    driving me nuts. The other five machines use a mixture of openSUSE 11.0,
    FreeBSD 7, and Vista Ultimate. To be sure that I wasn't suffering from
    a hardware failure, I rebooted my openSUSE 11.1 machine using an
    openSUSE 11.0 KDE LiveCD and experienced _no_ network issues at all.
    Something in openSUSE 11.1 is broke, whether its DNS or IPv6 I'm not
    certain. I'll have to experiment some more to try to determine what
    -- if anything -- will fix this.

  4. #4

    Default Re: dns lookup not working

    Someone on the openSUSE mail list found same thing, disabling IPv6 needed for DNS lookup to work.

    It's puzzled me, when I've come across the issue, as it's been a bit of a habit to disable IPv6, when I get to configure network devices. I get bitten when I forget, and then of course it's worked later, after I've gone and checked things, without me spotting the connection.

    It's plausbile, Ubuntu had to re-release their last LTS I think, due to a similar problem.

  5. #5

    Default Re: dns lookup not working

    I can second (or whatever) this problem. It seems that the IPv6 and DNS interaction has caused me to have problems on my x86_64 OpenSuSE 11.1 install. It seems that the priority in the network stack is given to IPv6 over IPv4. As such DNS lookups must be happening using IPv6. Since the majority of name servers out there don't support IPv6, the resolution fails. However, I have found that subsequent lookups (or performing the lookup in a terminal window of the address, which puts the name lookup result into nscd - the name service cache) that the thing you wish to run then works. So, it looks like things are able to pull name service resolution out of the cache using IPv4 but the initial query is done using IPv6 (and then probably failing over to IPv4).

    The easiest solution, as has been mentioned, is to disable IPv6. However, this doesn't mean that I wouldn't like an answer as to why the dual stack isn't working! I really don't like turning things off that should be working properly and ignoring them though from a security POV turning things off is generally a Good Thing.

  6. #6
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    Default Re: dns lookup not working

    Actually it's more complicated than that.

    There is DNS lookup via IPv6, and there is DNS lookup for IPv6 names on IPv4.

    IPv6 lookups will go no further than your router since it's highly unlikely that your link to your ISP supports IPv6 transmission. It is possible though that your stub libraries are sending out IPv6 queries and that your resolver (router) is blocking on the lookup, and blocking the IPv4 query. To check this one would have to sniff the packets to the router.

    IPv6 names via IPv6 lookup is initiated by the stub libraries in libc, it's a query for an AAAA record. I have found that some brain-damaged resolvers in routers return bad results for AAAA queries and that not using such resolvers fixes the problem. However I am mystified why the common advice of turning off the IPv6 stack is supposed to solve this since this is a IPv4 transaction, and at the time I looked, about a year ago, there was no way to turn off AAAA queries in libc. Maybe there is now. At the time I thought it a poor design that there was no way to configure libc stub libraries to not send AAAA queries.

  7. #7
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    Default Re: dns lookup not working

    PS: Here's the link to my post sometime back about broken proxies in embedded routers returning bad results.

    Broken Routers And Disabling Ipv6 - openSUSE Forums

    So I still don't understand why disabling the IPv6 stack works, if it really does. I don't have access to that LAN anymore so I can't do any experiments on the problem.

  8. #8

    Default Re: dns lookup not working

    I am not sure as to whether it is down to the DNS proxy on my router. The DNS IP addresses that my router provides via DHCP is not itself and so it should not be caching any queries that I may be making myself. I am querying my ISPs DNS servers directly (as well as the OpenDNS ones). So if the DNS proxy on my router is broken (it is a Draytek 2820Vn) then it really doesn't matter as all I care about are my ISPs DNS servers (or whoever I am querying).

    I should add that the problem doesn't manifest itself under OpenSuSE 11.0 - it is only under 11.1. So, somewhere along the line something has changed, which is what the initial post was concerning itself with.

    Performing digs, as per your suggestion, directly to my router, directly to my ISPs DNS servers and directly to the OpenDNS DNS servers results in no response from the router for IPv6 AAAA queries but does yield IPv4 A records (as one would expect). If it helps then I can install Wireshark and perform some packet dumps.

  9. #9

    Default Re: dns lookup not working

    I can confirm this as well, and as I have one 11.0 box and my 11.1 box running on the same network (11.0 which works fine with IPV6 and the newly installed 11.1 which was having issues), I can also confirm it being a new development.

    Disabling IPv6 does indeed "fix" the problem. The first problem I noticed was Firefox taking forever to load pages. Don't remember why but I ended up disabling IPv6 within FF and that worked for FF. However, yast package management was also taking forever, and some servers (most notably NVIDIA) were almost never resolved. Email and other programs were having issues too, so finally I decided (even though I didn't want to) to disable IPv6 in yast. This "fixed" the issues system wide.

    I am also glad to provide any information to help track down the foe. If it helps, I'm running 64-bit.

    --Jason

  10. #10
    Thetaotao NNTP User

    Default Re: dns lookup not working

    I updated from 11.0 to 11.1 today. I've set everything in /etc/sysconfig with ipv6 in the name to no as well as adding some entries to /etc/modprobe.conf. and DNS is still not working. I'm not too great with this so could anyone give me some advice how to do this properly?
    I've definitely got my connection working in general because i'm pinging everything fine.

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