Confused about DNS - Aix

This is a discussion on Confused about DNS - Aix ; If my DNS servers (windows boxes) go down, my AIX box really starts suffering. Things start taking ages. Similarly my IHS/apache web servers take ages to start at the moment, even with apparently working DNS (*) - if I set ...

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Thread: Confused about DNS

  1. Confused about DNS

    If my DNS servers (windows boxes) go down, my AIX box really starts
    suffering. Things start taking ages.

    Similarly my IHS/apache web servers take ages to start at the moment, even
    with apparently working DNS (*) - if I set NSORDER=local, they start
    quickly.

    (* I say apparently working - I know my DNS servers don't know about my AIX
    box, but I do have appropriate entries in /etc/hosts. Well, I hope I do...)

    I see plenty of references to this sort of thing around the place, and the
    answer given is always "Sort out your DNS".

    Can anybody tell me more detail on this? Eg when it's waiting, what is it
    waiting for?

    cheers,
    clive



  2. Re: Confused about DNS

    On Aug 4, 7:01*pm, "Clive George" wrote:
    > If my DNS servers (windows boxes) go down, my AIX box really starts
    > suffering. Things start taking ages.
    >
    > Similarly my IHS/apache web servers take ages to start at the moment, even
    > with apparently working DNS (*) - if I set NSORDER=local, they start
    > quickly.
    >
    > (* I say apparently working - I know my DNS servers don't know about my AIX
    > box, but I do have appropriate entries in /etc/hosts. Well, I hope I do....)
    >
    > I see plenty of references to this sort of thing around the place, and the
    > answer given is always "Sort out your DNS".
    >
    > Can anybody tell me more detail on this? Eg when it's waiting, what is it
    > waiting for?
    >
    > cheers,
    > clive


    Well what happens is any time hostnames are used they have to be
    translated into an actually tcpip address.
    For example if you were to try and telnet to a host thats not in your
    local hosts file or dns it trys to send those request out for someone
    to resolve it.

    So in your case if Apache is using hostnames to start services or
    communicate with other servers you my get about a minute and 1/2 delay
    until it gives up trying to resolve. You can sometimes see this if
    you telnet to a system and it can not resolve the incoming up ip
    address it will to appear to hang for about 11/2 minutes until the dns
    lookup fails. You can change the delay so its shorter but best thing
    to do is have local entries for at least your critical ips in your
    local host table i.e the servers own ip address and any critcal
    servers it talks to locally on the network. Then Have your DNS
    windows people give you a list of dns servers and add them to your /
    etc/resolv.conf file so it can do a search order so if 1 DNS servers
    not available it will roll down to the next one.

    So in short -
    1. edit you /etc/netsvc.conf file put line hosts=local,bind4
    which says search the local host file first if not matches then go to
    DNS servers - listed in your /etc/resolv.conf

    2.You can see what dns server your talking to for example try taking
    out a known host from your /etc/hosts files then do a nslookup
    "hostname" where hostname is the name of the server and it will show
    what server is resolving it. Like wise you can also check to see if a
    ip address resolves by typing host "ipaddress"

    Hope this helps a little.
    -Mp

  3. Re: Confused about DNS

    "Clive George" wrote in message
    news:gc2dnR5_C6UqKQrVnZ2dnUVZ8hidnZ2d@posted.plusn et...
    > If my DNS servers (windows boxes) go down, my AIX box really starts
    > suffering. Things start taking ages.
    >
    > Similarly my IHS/apache web servers take ages to start at the moment, even
    > with apparently working DNS (*) - if I set NSORDER=local, they start
    > quickly.
    >
    > (* I say apparently working - I know my DNS servers don't know about my
    > AIX box, but I do have appropriate entries in /etc/hosts. Well, I hope I
    > do...)


    For the record, it turns out it was IPv6 breaking things - apache was trying
    to do a lookup on ipv6 for the Listen directive, and our setup doesn't
    really support that. Change the Listen 80 to Listen 0.0.0.0:80 and it all
    starts working fine.

    Now to see what happens when I pull the DNS from under the machine's feet
    (ie if it copes)...

    cheers,
    clive



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