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DNS Caching problem

    Question

  • Hi

    I have a company network with 2 internal dns servers on 192.168.0.7 and 192.168.0.9.

    Using DHCP.

    2 problem Win7 clients.

    When I run ipconfig /all on both it shows both DNS servers as expected 

    We have a corporate server on AWS and it's IP address changed on Monday during a restart.

    Shouldn't have but it did, so we are stuck with a new public facing DNS name for that server, so we updated the friendly CNAME record to point to the new address.

    18 of our 20 internal clients, including Win7, 8 and 10 clients and Mac and Linux clients are all finding the corporate server now using the original friendly name.

    But 2 Win7 clients are still not getting there.

    On both, if we run

    nslookup <friendly.domname.com>

    It returns the name of of our primary internal DNS server (as nameserver) and the NEW IP address of the host address

    So it seems that the client's base OS DNS lookup returns the correct IP.

    If I paste that IP into either chrome or Internet Explorer, I get the correct website.

    However, if I enter <friendly.domname.com> into either browser (and Firefox) a different website appears.

    I can in Chrome test the dns resolver using chrome://net-internals/#dns which returns a list of addresses in chromes internal cache.

    And I can flush that browser dns cache by clicking the "clear host cache" button

    If I then try the same <friendly.domname.com> again, the cache list is re-populated with a bunch of urls accessed including

    friendly.domname.com IPV4
    <old.ip.add.ress>
    3600000 2017-07-12 16:03:48.836 677

    Which seems to indicate that the old ip address is now reused on the cloud and somehow the browser is overriding the settings in the actual DNS to resolve to a cached version.

    In IE we have tried deleting history and cookies without effect. 

    Not sure if there is a facility to do something similar on IE to what Chrome does with DNS.

    But ALL browsers on these 2 machines are still looking at the old ip address despite DNS saying something else.

    How do I flush the entire machine and start from scratch dns-wise?

    Thanks

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    This issue was originally raised on a community forum and the advice there was to raise it here.

    https://answers.microsoft.com/en-us/windows/forum/windows_7-networking/dns-caching-problem/9419d824-93d3-4a38-a357-d2e0da755789




    Monday, July 17, 2017 8:38 AM

All replies

  • Hi,

    Please run the following command as administrator to clean DNS and Netbios cache.

    ipconfig /flushdns

    NBTSTAT -R

    Then, run command “ipconfig /displaydns” as administrator to check the DNS client resolver cache.

    Please check “host file” in c:\Windows\System32\Drivers\etc\hosts again.

    By the way, instead of using browser, we could use Windows Explorer to access the address.

    Moreover,  we could use process monitor to check the detailed information.

    Best regards,

    Joy.


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    Tuesday, July 18, 2017 10:21 AM
    Moderator