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DNS Probleme

Posted on 2011-09-14
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Last Modified: 2012-05-12
I have two domain controler (replicate) them and are DNS on Windows 2008 R2
In fact on opening a web page html we encounter a big problem with DNS.
it joined the snappshot Wireshark shows the multiple DNS requests to open a web page.
must be 3 to 4 DNS requests and about 30 seconds before the pc has an answer.
This problem of DNS is present only when one makes use of www pages, but I do not have the same problem on the Intranet that they are hard in our DNS.
please help me because the internet is becoming very slow
thank you very much
DNS.jpg
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Question by:DRRAM
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10 Comments
 
LVL 9

Expert Comment

by:Michael Knight
ID: 36538747
Why are you assuming it's DNS and not network congestion? The fact that the DNS request takes a while doesn't necessarily mean it's the servers. Likewise, the fact that the intranet application performs quickly does not point to a DNS problem. The machines will keep a cache of DNS on their local machine for domains that have been visited, so if it takes 30 seconds for google to come up lets say, I'd lean more towards a slow connection. The Intranet app would be faster in any instance seeing that it is on the Local Network. If you wanna test DNS for sure, change one of the local machines DNS to 4.2.2.1 4.2.2.2 and see if the connection speed improves, if not you have network congestion or a shoddy modem/connection.
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Expert Comment

by:Michael Knight
ID: 36538754
or a bad router.
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LVL 6

Expert Comment

by:da3ve
ID: 36538864
I assume your DC is configured as your DNS. If your only problem is the speed that the DNS returns resolved names and if you fave no related entries in the event logs, I would start by checking the DNS Forwarder settings.

In the DNS server properties, you should see a "Forwarders" tab.
DNS_screenshotThe forwarders should be external DNS servers (either your external DNS servers or your ISP's DNS servers). When you make the DNS request, your DNS server (on the DC) is forwarding unknown names out to the listed servers. If the first server is unreachable, it will take some time for the request to time out and then your DNS will request resolution from the next listed server. For troubleshooting purposes, you can move the first listed DNS forwarder down the list to see if your performance improves.

If things improve, you will then troubleshoot why that DNS server isn't working correctly.

I would use a nameserver benchmark program to examine DNS server response times. The server with the best response should be your primary DNS forwarder.

Check out these:
http://code.google.com/p/namebench/
http://pflog.net/ns_bench/

Hope this helps.
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Author Comment

by:DRRAM
ID: 36538951
I try with another DNS server I have an answer after one query
please you know a tool for test the dns (replicat dns 1 and dns 2) and find out where the probems
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Author Comment

by:DRRAM
ID: 36539019
da3ve:
The forwarders contient only external DNS servers and my DNS server (on the DC) is not includ in the DNS Forwarder settings.???
Thx
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LVL 6

Accepted Solution

by:
da3ve earned 500 total points
ID: 36539542
That is correct. Your DNS on the DC is resolving host names internal to the domain. For name resolution of names outside your network, your DNS server forwards requests to your ISP's (or your external) DNS servers.

The DNS looks at the forwarders list in order. If your primary forwarder is offline, it will take some time for your request to be resolved.

Check out this technet link for more info:

http://technet.microsoft.com/en-us/library/cc757172(WS.10).aspx
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Author Comment

by:DRRAM
ID: 36539658
da3ve

exemple j'ai deux DC (DNS installer sur les deux)
@ IP DC1:10.10.10.7 (DNS1) replication avec
@ IP DC2:10.10.10.9 (DNS2)
DNS Forwarder settings:
@IP:154.xx.xx.12
@IP: 144.xx.xx.45
utilisateur (PC) essaie de joindre ce site "http://xxx.com"
etape:
PC --> DC1(DNS1) si il trouve la reponse dans ce cas il repond
si il ne trouve pas il envoie au DNS Forwarder pour chercher à l'exterieur
confirme please thx
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LVL 9

Expert Comment

by:Michael Knight
ID: 36540153
You're slipping in and out of english, but it would appear that the setup is OK which brings me to my original point.

Try bypassing your DNS servers entirely. On one of the workstations (not the server) change the DNS settings on the local machine to 8.8.8.8 and 8.8.4.4 (Google's Public DNS servers) then at the command prompt type: ipconfig /flushdns

now try to see if your connection speed is any quicker. If so, you can change your forwarders to the above and you should be OK. It could just be that your primary forwarder is down, it happens. You're not going to hurt anything by using Google's Public DNS as your forwarders.
If that doesn't help, you likely have other network issues not necessarily related to DNS.

Are you getting anything in the event logs?

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LVL 6

Expert Comment

by:da3ve
ID: 36540156
Correct. Your DNS server is only able to respond to requests for .your_domain.com. If your DNS gets a client request for www.xxx.com, it forwards the request on to a server that can answer that request.

I am guessing that the 154.xx.xx.12 server isn't responding to requests. When a DNS server doesn't get a response, as you can see on your wireshark screen, it moves on to the next server in the list.

I would also look at a client that is having trouble. Check the DNS settings on the client machine and ensure that it is pointing at 10.10.10.7 or 10.10.10.9. If your clients aren't using your x.7 or x.9 machines for DNS, you will have to find out were they are sending DNS requests.
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Author Closing Comment

by:DRRAM
ID: 36556991
thx
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