How can I setup my DNS when my ISP DNS crashes

Discussion in 'Linux Networking' started by Joaco, Dec 16, 2003.

  1. Joaco

    Joaco Guest

    Running bind 9.1.2 with an internal and an external zone.

    Frequently, now days, my ISP's servers crash and my two local
    dns servers then fail to provide external name resolution during
    those lapses. My WWW/FTP servers remain visible to the outside,
    because I switched to Netsol for my domain's external DNS.
    However, I am now blind internally and end up having to go to for manual name resolution...

    Question, I do have a "." zone and db.root defined, but no joy.
    How do I get bind to feed its cache from the internet root
    servers, when my ISP forwarders are down???

    Joaco, Dec 16, 2003
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  2. Joaco

    Neil Horman Guest

    Red Hat supplies a caching dns server config rpm. I'd go install that,
    or just unpack the files out of it if your using another distro, and use
    them stock or as a guide for your own config.
    Neil Horman, Dec 16, 2003
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  3. Joaco

    Leon. Guest

    You can read entries out ofthe db.root file and stick them in to the
    bind.conf file as forwarders.

    Or you can just use root servers full time.

    Whats wrong with letting them use root servers at all times ?
    The only thing is that if the isp is disconnect from the internet, you cant
    get DNS lookups for the ISP to check their status pages to see how they are
    going at fixing their problem. Not that the status pages ever record 100%
    failure things - they more often tell you about leaves removed from the
    gutters of the building the pop is in.

    ( you could 'secondary' the ISP's dns pages on your local system, if the
    isp's dns server lets you )
    Leon., Dec 17, 2003
  4. Joaco

    Leon. Guest

    If you really want to get sophisticated,

    you could write a script to check that the DNS servers are working.

    if the script detects failure,

    swap over the bind.conf file and send bind a SIGHUP signal to tell it to
    reload its configuration,
    and then dns is using the root servers.

    When the script detects the ISP dns servers are back up, swap over conf
    files and reconfigure it back.

    But this seems a bit drastic, why not just add more forwarders.
    Leon., Dec 17, 2003
  5. What do you have in your named.conf for anything related to forward (do
    you have 'forward only')?

    I do not use forwarders because when I first got DSL, Ameritech's DNS was
    sluggish at times, which was my reason for doing my own caching DNS. If
    you do not rely on unreliable servers, you will not be affected by them.
    However, you have to occasionally keep your db.root file up to date
    (assuming db.root is same as root.hints in SuSE):

    cp db.root db.root.old
    dig @server . ns > db.root (where server is any root server in db.root)

    I do not know how often a name I access might be in my ISP's cache or
    whether they would need to fetch it from the root servers. But fetching a
    name once and having it in my local cache has got to be quicker than
    'forward first' every name request to my ISP.
    David Efflandt, Dec 17, 2003
  6. Joaco

    George Bell Guest

    Why? You seem to be implying here, that no caching occurs if the result is
    returned via 'forward first'. Well, if that's how it works, then why is
    this setup often referred to as a "caching DNS server" ?

    I think that, unless your ISP's DNS server is fairly unreliable, name
    lookups will generally be faster with forward because there's a good chance
    it will already be cached there, and after it is fetched, it'd be cached at
    your local host( or am I totally confused here? ).

    George Bell, Dec 17, 2003
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