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DC failover not happening... Need advice

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  • DC failover not happening... Need advice

    We have 3 sites each with its own DC. Each DC has full AD, AD integrated DNS, File and Print sharing with DFS, IAS or NPS and WINS. Our DHCP is handled by an onsite router.

    Each site is has its own router, and each router connects to an MPLS network.

    The problem is that when a domain controller goes down, users in that site can log in only if they have cached credentials on that machine. What do I need to do to get it to work? If a DC goes down, I thought the client machines would automatically pick a different DC. Also all PCs have all three DNS servers added to their DNS list.

  • #2
    Re: DC failover not happening... Need advice

    check in your DNS "_LDAP._tcp.dc._msdcs.domainname"
    if all your Domain controllers are there.

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    • #3
      Re: DC failover not happening... Need advice

      Yup all of them are there

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      • #4
        Re: DC failover not happening... Need advice

        ok, assuming you got one DC per site, The DC holds the DNS service, when that DC is down, the question remains, do the clients have a secondary
        DNS to answer their calls? i.e. are they configured with Primary/Secondary DNS in their TCP/IP settings?
        Last edited by Akila; 3rd November 2008, 20:49.

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        • #5
          Re: DC failover not happening... Need advice

          All clients have the three DC's listed as secondary and a third dns servers. For instance, in the main branch you have 192.168.1.3 as primary then 192.168.2.3 as a secondary and finally 192.168.3.3 for the 3rd listing.

          It was my assumption if they couldn't contact 192.168.1.3 they would try 2.3

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          • #6
            Re: DC failover not happening... Need advice

            only if the Primary DNS is offline (not pingable).
            if the DNS is online the client would not fail over to the secondary DNS even if the DNS service is off.

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            • #7
              Re: DC failover not happening... Need advice

              That would make sense then. So if I don't have DNS available at that address but the address is pingable, then it won't go to another DNS server

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              • #8
                Re: DC failover not happening... Need advice

                on the domain where the DC has failed is the DNS service still up and runnig? Can you ping that failed DC box? If yes, then do a nslookup from one of the client machines and see if the second/third DNS server reply back.

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                • #9
                  Re: DC failover not happening... Need advice

                  When the DC fails, aka i shut it down for hardware maintenance, the DNS goes down with it due to it being the only server in that location.

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                  • #10
                    Re: DC failover not happening... Need advice

                    whenever you do that next,see if the clients from that site get a response back using nslookup from the other dns servers. they should after a small lag if they have the ip address of those boxes provided to them from DHCP. If they can query those dns boxes they should get the other dc's information from there on.

                    my thought process only. Could be wrong.

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                    • #11
                      Re: DC failover not happening... Need advice

                      i will definitely try that

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                      • #12
                        Re: DC failover not happening... Need advice

                        from what I know a little about AD the dc locator process looks for a dc in this order

                        subnet > site > domain

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                        • #13
                          Re: DC failover not happening... Need advice

                          Originally posted by glacieredlightning View Post
                          from what I know a little about AD the dc locator process looks for a dc in this order

                          subnet > site > domain
                          Yes, but that would be if there is a DNS server to answer that call.

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                          • #14
                            Re: DC failover not happening... Need advice

                            There should be a DNS server to answer the call due to the fact that there would be 2 other dc/dns servers online at the time.

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