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Wireless Networks Thread, DNS Woes. in Technical; We're currently setting up our new domain, and everything is going fairly well except I've been noticing problems with the ...
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    maniac's Avatar
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    DNS Woes.

    We're currently setting up our new domain, and everything is going fairly well except I've been noticing problems with the internet hanging recently so decide to investigate. First thing I do is test DNS lookups, and I notice that anything external to the school is timing out quite frequently so I ring county support to see if they're having any issues with their DNS servers (as it's only external addresses affected) they say no, but have a look into it with me anyway and discover than my first DNS server is resolving external addresses intermitently, and my second isn't resolving external addresses at all!

    I look into it a bit more and discover the reason that the first one is intermittent is because one of the forwarding DNS addresses is entered wrong, I correct that and it all springs into life. My second server however had the correct forwarding addresses, but is still refusing point blank to resolve any addresses external to the school.

    It's set-up as a secondary DNS server taking its data from the first, but I'm wondering if it should actually be a primary DNS server in its own right - could this be where I'm going wrong? I've checked all the other settings, and everything else is absolutely correct, the only difference is one is a primary DNS server and the other is a secondary DNS server. It resolves internal addresses absolutely fine.

    Anyone shed some light on this?

    Mike.

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    leco's Avatar
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    I don't know if this is even the right thing to do but I have two servers, each one points to itself as Primary and to the other as secondary. They each appear to resolve internal and external addresses fine.

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    tmcd35's Avatar
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    I tend to go for a 3 dns server set up.

    server 1 - itself then external host dns
    server 2 - itself then server 1
    server 3 - itself then server 1

    DHCP sets clients to query server 3 then server 2. Clients with static IP's are set to query server 2 then server 3.

    I find this give a good level of load balancing and fault tolerance between the dns servers.

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    maniac's Avatar
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    Quote Originally Posted by tmcd35 View Post
    I tend to go for a 3 dns server set up.

    server 1 - itself then external host dns
    server 2 - itself then server 1
    server 3 - itself then server 1

    DHCP sets clients to query server 3 then server 2. Clients with static IP's are set to query server 2 then server 3.

    I find this give a good level of load balancing and fault tolerance between the dns servers.
    The problem with that setup is if Server 1 dies for whatever reason, you lose the ability to resolve external addresses. I'm aiming for a high fault tolerance here, so want them to both resolve external addresses independantly if possible.

    I'm going to remove and re-setup DNS on the second server I think, see if that makes any difference.

    Mike.

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    tmcd35's Avatar
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    I also prefer to run DNS, as with most servers, on a virtual machine. Let's face it, once it's set up it's hardly going to go wrong for software failure reasons. The big bonus with VMs is if a hosting physical server has hardware probs it's childs play (and less than a few seconds work) to restart the effected VM's on another host.

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    RabbieBurns's Avatar
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    Am i wrong in thinking the DNS servers all know the root dns zones, so dont in theory need any forwarder at all- if they dont know the ip for something they are asked to resolve, they then just pass it on up?

    My DNS servers point to themselves then each other as primary and secondary, I dont have any forwarding set up, and clients get the 2 dns servers as primary and secondary, which I allocated in no order.

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    mattx's Avatar
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    Quote Originally Posted by RabbieBurns View Post
    ...if they dont know the ip for something they are asked to resolve, they then just pass it on up?.
    Indeed and in that list should be your gateway address...... [ if you want it to look for it on the internetthingymebob ]

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    Quote Originally Posted by RabbieBurns View Post
    Am i wrong in thinking the DNS servers all know the root dns zones, so dont in theory need any forwarder at all- if they dont know the ip for something they are asked to resolve, they then just pass it on up?
    Correct, you'll just loose the advantages of any caching another upstream server may have done. So each (un-cached request) will require asking a root server for the appropriate primary server to query for the given domain. Generally it's worth having and making use of lower levels of DNS.

    Quote Originally Posted by maniac;
    It's set-up as a secondary DNS server taking its data from the first, but I'm wondering if it should actually be a primary DNS server in its own right - could this be where I'm going wrong? I've checked all the other settings, and everything else is absolutely correct, the only difference is one is a primary DNS server and the other is a secondary DNS server. It resolves internal addresses absolutely fine.
    What OS/system are you running? From what you've described the setup is pretty normal, does the secondary server resolve external names correctly itself or does it fail external lookups?

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