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  • DNS resolving question

    Hi,

    I am looking for a web site ot a tool which can resolve my subdomain/domain from multiple DNS server locations.

    basickly when I change the A-record for a Subdomain, I would like to see if all DNS servers have been updated with the new IP.

    Thanks,
    Michael

  • #2
    Re: DNS resolving question

    The sub-domain will usually be the only DNS server(s) that has the host record for its domain and the parent a glue A record for the sub-domain DNS, if you have delegated authority.

    Can you give give us more info.

    What DNS servers are you using?

    If relevant, is it AD integrated, Primary/Secondary setup etc.

    Is it an AD environment?

    Are the DNS servers located on different sites and subnets?

    Any firewalls in the way?

    Comment


    • #3
      Re: DNS resolving question

      Hi,

      I am affraid I haven't been clear. let me rewrite the question:

      What I ment was that I have A web site. sometimes I am doing Maintenance work on the server and changing the domain (www.blabla.com) IP to another location/server IP.

      Before I am shuting down the original server, I would like to be sure that the new IP has been updated in all/many DNS server over the globe.

      Is there a tool which checks the domain resolotion in multiple global DNS servers ?

      Thanks,
      michael

      Comment


      • #4
        Re: DNS resolving question

        No not really but if you wait a couple of days then it will be replicated.
        Usually it's been replicated between 48-72 hours
        Change it on a friday and shutdown the old server at sunday or so
        Marcel
        Technical Consultant
        Netherlands
        http://www.phetios.com
        http://blog.nessus.nl

        MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
        "No matter how secure, there is always the human factor."

        "Enjoy life today, tomorrow may never come."
        "If you're going through hell, keep going. ~Winston Churchill"

        Comment


        • #5
          Re: DNS resolving question

          ofcourse
          Thanks

          Comment


          • #6
            Re: DNS resolving question

            A couple of points to note:

            1. DNS records don't "propogate" or "update on servers around the globe". The only DNS servers that have your records are your DNS servers (or whomever hosts your DNS namespace). Other servers merely cache your record for the period of the TTL of the record.

            2. When someone does a lookup for your DNS records, (A, CNAME, MX, NS, etc.) their DNS server queries their forwarders or the root servers for the SOA and NS for your domain. Their DNS servers and their DNS resolver then cache the record for the period of the TTL. When you change the record it will be immediately available to DNS resolvers that don't have it in their cache. For DNS resolvers who have it in their cache it won't be available until the TTL for the record expires and they do a new lookup for the record. This situation will affect a very small number of users who have looked up your record and cached it during the time right before you changed the record.

            3. The only record changes that can take 24 to 72 hours are changes to your SOA and NS records as those records do need to be reflected in the TLD DNS servers that your domain resides in (.com, .edu, etc.) and that can take a while to be reflected in the TLD name servers as these servers only get update every few days or so.

            Comment


            • #7
              Re: DNS resolving question

              Thank you very much for your understandable explanation.

              Michael

              Comment


              • #8
                Re: DNS resolving question

                Nice explanation but the TTL of caching is often longer then you wish for, sadly enough.
                Simply doing it over the weekend and your safe.

                It wouldn't be the first that I've seen that webservers or mailservers where inaccessible due to fast switching.
                Marcel
                Technical Consultant
                Netherlands
                http://www.phetios.com
                http://blog.nessus.nl

                MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                "No matter how secure, there is always the human factor."

                "Enjoy life today, tomorrow may never come."
                "If you're going through hell, keep going. ~Winston Churchill"

                Comment


                • #9
                  Re: DNS resolving question

                  Originally posted by joeqwerty View Post
                  For DNS resolvers who have it in their cache it won't be available until the TTL for the record expires and they do a new lookup for the record.
                  It seems that some DNS servers out there have been set to ignore the TTL value though. The DNS admins sometimes force the servers to hold onto records longer. I'm not sure how widespread it is, but it's not uncommon. I find it annoying in certain circumstances when you want an ultralow TTL value.
                  Wesley David
                  LinkedIn | Careers 2.0
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                  Comment


                  • #10
                    Re: DNS resolving question

                    It would be good if every DNS admin keeps it on the standard TTL values (either raising it worldwide if needed) or leave it as is.
                    It would save me a couple headache
                    Marcel
                    Technical Consultant
                    Netherlands
                    http://www.phetios.com
                    http://blog.nessus.nl

                    MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                    "No matter how secure, there is always the human factor."

                    "Enjoy life today, tomorrow may never come."
                    "If you're going through hell, keep going. ~Winston Churchill"

                    Comment

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