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  • Can't access SOME websites - DNS related issue

    Hi everyone!

    I'm on a domain network run by a SBS 2008 server, and with 3-4 clients running Win 7 Pro 32 bits.

    As part of my job I'm working on 2 websites, which I access via FTP quite often. Since a week or two, I can't seem to be able to access these websites anymore. I thought they had a problem, but then I realized I can ping them, connect to them via a proxy, or simply from my home.

    From any computer on the work domain, they are not accessible. From any other computer, they seem accessible. Yesterday, I was even unable to connect via FTP to one of them (didn't try the other one), which never happened before. Though today I have FTP access again.

    Leaving the FTP anomaly aside for now, I worked around the problem by changing the DNS on my work station from 192.168.1.100 (the SBS 2008 server) to an OpenDNS address. It solved everything, so I pretty much know it's DNS related.

    But I want to be able to keep using my 2008 server as DNS server. What's going wrong? I don't have much clue as to how to troubleshoot this.

    I tried already:
    • ipconfig /flushdns on my work station and on the server.
    • Using different browsers and different computers on the domain


    I suspect/think:
    • I suspect a DNS caching issue (since it happens ONLY on 2 websites I visit very frequently to work on, (though it doesn't happen on Google Apps which I use even more often)). Hence the /flushdns, but nothing changed.
    • I suspected the router, but since changing the DNS on a client machine solves the pb, it doesn't make sense.
    • I read about MTU... but again, different DNS = no problem, so that shouldn't be it.
    • There is no firewall/antivirus on the SBS 2008 (fresh install), so that's not an issue.



    I would appreciate any help or suggestion... Thanks a lot!!

    Olivier


    Here is the result of an ipconfig /all from my work station:

    Code:
    Windows IP Configuration
    
       Host Name . . . . . . . . . . . . : COMPANYNAME-3
       Primary Dns Suffix  . . . . . . . : companyname.local
       Node Type . . . . . . . . . . . . : Hybrid
       IP Routing Enabled. . . . . . . . : No
       WINS Proxy Enabled. . . . . . . . : No
       DNS Suffix Search List. . . . . . : companyname.local
    
    Ethernet adapter Local Area Connection:
    
       Connection-specific DNS Suffix  . : companyname.local
       Description . . . . . . . . . . . : Intel(R) PRO/100 VE Network Connection
       Physical Address. . . . . . . . . : 00-12-3F-BB-01-77
       DHCP Enabled. . . . . . . . . . . : Yes
       Autoconfiguration Enabled . . . . : Yes
       Link-local IPv6 Address . . . . . : fe80::5c4f:e3ac:136e:911d%10(Preferred) 
       IPv4 Address. . . . . . . . . . . : 192.168.1.112(Preferred) 
       Subnet Mask . . . . . . . . . . . : 255.255.255.0
       Lease Obtained. . . . . . . . . . : Thursday, September 01, 2011 9:15:01 AM
       Lease Expires . . . . . . . . . . : Friday, September 09, 2011 10:34:04 AM
       Default Gateway . . . . . . . . . : 192.168.1.254
       DHCP Server . . . . . . . . . . . : 192.168.1.100
       DHCPv6 IAID . . . . . . . . . . . : 234885695
       DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-13-BC-39-94-00-12-3F-BB-01-77
       DNS Servers . . . . . . . . . . . : 192.168.1.100
       NetBIOS over Tcpip. . . . . . . . : Enabled
    
    Tunnel adapter Local Area Connection* 11:
    
       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . : 
       Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes
    
    Tunnel adapter isatap.companyname.local:
    
       Media State . . . . . . . . . . . : Media disconnected
       Connection-specific DNS Suffix  . : 
       Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
       Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
       DHCP Enabled. . . . . . . . . . . : No
       Autoconfiguration Enabled . . . . : Yes
    Last edited by nomade0; 7th September 2011, 20:50. Reason: adding ipconfig /all details

  • #2
    Re: Can't access SOME websites - DNS related issue

    Run nslookup and query the site names you're having issues with against your SBS server and then against OpenDNS and let us know what you got back. (Let me know if you have questions about using nslookup)

    One thing you might want to check is the forwarders configured on your SBS 2008's DNS server. (Open DNS console, right-click on the server and select the forwarders tab) Make sure you're using valid, known good DNS server.

    BTW, you can use the DNS Benchmark tool to find close, fast DNS servers.
    http://www.grc.com/dns/benchmark.htm
    Regards,
    Jeremy

    Network Consultant/Engineer
    Baltimore - Washington area and beyond
    www.gma-cpa.com

    Comment


    • #3
      Re: Can't access SOME websites - DNS related issue

      Hi JeremyW, thanks for helping out. Sorry for the delay of my response, I'm just returning to work after labor day weekend.

      I'm not that familiar with the nslookup tool, but here is what I got.

      From my client computer, using the server as DNS.
      Code:
      Default Server:  server.companyname.local
      Address:  192.168.1.100
      
      > gratefulhearttherapy.org
      Server:  server.companyname.local
      Address:  192.168.1.100
      
      *** server.companyname.local can't find gratefulhearttherapy.org: Server failed
      >
      From my client computer, using OpenDNS as DNS:

      Code:
      Default Server:  resolver1.opendns.com
      Address:  208.67.222.222
      
      > gratefulhearttherapy.org
      Server:  resolver1.opendns.com
      Address:  208.67.222.222
      
      Non-authoritative answer:
      Name:    gratefulhearttherapy.org
      Address:  70.32.114.161
      >
      When I go to check for Forwarders, it's empty. No forwarder is set up... It seems like an easy solution to set up as many as possible, is there any drawback to doing that?

      I'll try to add OpenDNS servers as forwarders. [UPDATE] OK, I just did, and it has solved my problem. Thanks! Now, is there any drawback or limitation with this set up I should be aware of?
      Last edited by nomade0; 7th September 2011, 20:48. Reason: johndoeing company name + updating resolution of problem

      Comment


      • #4
        Re: Can't access SOME websites - DNS related issue

        Nope. Most setups should use forwarders.

        Glad to help!
        Regards,
        Jeremy

        Network Consultant/Engineer
        Baltimore - Washington area and beyond
        www.gma-cpa.com

        Comment

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