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Thread: HowTo simulate DNS settings

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    easytouch's Avatar
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    Question HowTo simulate DNS settings

    I want to setup a spare server for disaster-recovery. (Zimbra OS Version on Debian)

    So it should have the same hostname and MX record as the production server.

    How can I fake the DNS settings like A record and MX record for the Zimbra binary installation at the moment of initial installation? (and for postifx after the installation procedure, if i let it run to test the spare server. therefore I would set the IP on my workstation through hosts file to point to the new server)

    how to do this on a local LAN without internet-access?
    and how on an internet-connected spare-server that has a different ip?

    If I can do this, it is possible to easily switch the DNs settings in case of desaster from the production machine to the spare-server.

    thanks in advance, robert
    Last edited by easytouch; 02-15-2007 at 05:18 AM.

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    Quote Originally Posted by easytouch View Post
    How can I fake the DNS settings like A record and MX record for the Zimbra binary at the moment of initial installation?
    These settings are guessed by the installation script (DNS queries) but are overidable.

    Why not just overide them once in the script instead of trying to fool the script by fake DNS (and taking risks with that) ?

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    Question which parts of install script to change?

    thx for the quick suggestion.

    If I set (on the spare server) in /etc/hosts/ the IP address of the production server, the unmodified installation looks at the MX Record and down to the 'real' IP from the external DNS servers. Aftwerwards zmapachectl is not ale to run.

    Which parts of the install script would I have to change? Could someone giveme a pointer?

    What If I had wrong settings in etc/hosts, or something related to IP's and DNS settings hase changed - where are the points to change the actual configuration by hand for a already installed system?

    thank you

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    Default Split-DNS

    I will try the way with Split-DNS

    http://wiki.zimbra.com/index.php?title=Split_dns

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    Quote Originally Posted by easytouch View Post
    Which parts of the install script would I have to change? Could someone giveme a pointer?
    You don't have to change anything IN the script.
    Just changes the parameters (answers to the script's questions).

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    wkruchas is offline Junior Member
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    Default Hello

    KLUG,
    I was searching through the forums, and found this thread. It seems close to the question I asked somewhere else unsuccesfully in another thread. But please let me ask it here again as I think you know the answer to my question.

    I would like to preload zimbra on a new server so that I can switch the servers friday nite. During the install the domain and mx records will not be valid, but will be when I switch the servers. Can I safely ignore the message that there does not seem to be a mx record for this domain. and go on with the installation? Will the zimbra install script "take my word" for the dns config and finish installing?

    What I am hoping I can do is.

    1)preload zimbra on new machine (not attached to network to not interrupt email now).
    2)Friday unplug existing non-zimbra email server.
    3)Turn on new pre loaded zimbra server.

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    bigmudcake is offline Banned
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    Quote Originally Posted by easytouch View Post
    I want to setup a spare server for disaster-recovery. (Zimbra OS Version on Debian)

    So it should have the same hostname and MX record as the production server.

    How can I fake the DNS settings like A record and MX record for the Zimbra binary installation at the moment of initial installation? (and for postifx after the installation procedure, if i let it run to test the spare server. therefore I would set the IP on my workstation through hosts file to point to the new server)

    how to do this on a local LAN without internet-access?
    and how on an internet-connected spare-server that has a different ip?

    If I can do this, it is possible to easily switch the DNs settings in case of desaster from the production machine to the spare-server.

    thanks in advance, robert

    The best way is to setup a DNS server on the spare computer and have the spare computer using its own DNS server rather than the external one (on linux this can be done by changing the DNS settings in resolv.conf).

    That way the spare computer no longer needs the outside world and therefore you can disconnect it from the outside networks for better security.

    Then to "activate" the spare just shutdown its internal DNS server, and change the resolv.conf to point to the "real" DNS server.

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    wkruchas is offline Junior Member
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    Default Another way

    Although I am sure setting up an internal dns server would have solved this also, I choose another route that in my case was more straight forward, and I wanted to share this.
    Anyway I added a second mx record for the domain with lower priority (higher number), this satisfied the installers need to check the mx, and allowed the current email to work until I was ready to make the change. Then all it took was changing the mx records and presto.. the new server was in place.
    I'm sure setting up an internal dns server has it's place, but why run an authoritative dns server unless you have too, most people register the domain name with a service, and everyone I have used dydns, godaddy, network solutions all give you a nice interface to maintain the dns records. The only possible reason might be a nated interface on a dynamic ip, but ddclient and port forwarding solved that for me on dyndns.
    Well I hope this makes someone else's transition as smooth as mine went.
    To the Zimbra Team: Thanks for such a great product.

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