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DNS resolution issues could this be cabling or DNS Server ?

Posted on 2008-10-15
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Last Modified: 2013-12-05
For the past couple of days I have had users complaining they cannot access the internet or access SQL(using SAGE 200 Accounting). Upon further investigation I find that the machines in question is very slow in resolving DNS names. Pinging by IP Address returns an anwser straight away; whereas on specific servers (eg SQL Server and the Domain Controller/DNS Server) I ping by it's name and nothing happens for around 5/10 seconds then it returns a healthy ping <1ms no dropped packets. Thats led me to believe that the slowness in name resolution has resulted in people not able to access the internet and get SQL error msg under SAGE (Bizzarely Outlook connected to Exchange still works ok). Now the way to get the machine working is either to:

1) Repair the Connection under XP
2) Plug the PC into a different switch port/another switch (they are a mixture of 100/1000mbits Layer 2)
3) Unplug the Cat5 Patch lead and change the physical CAT5 Port
4) Reboot whatever switch the PC(s) are plugged into.

This cures the issue for a few minutes then it will return, also of note:

1) It always happens to the same group of PCs (intermittently; not always at the same time)
2) I have rebooted both Domain Controllers (also DNS Servers themselves: Windows 2000 Server SP4) There is no notable DNS issues in Event Viewer..same with PCs..no Event ID of note. They are all running Windows XP SP2 by the way

Things I will try:

There is a central switch that all the servers are attached to. this is a 24port Gigabit switch that all other switches attach to. I have rebooted all of this and I have ordered a new 3Com 24 Port Switch to replace it just in case this week.

I will also hire a Network Meter to test all the cabling to ensure the horizontal cabling is not damaged (if it was a Switch or DNS Server issue surely it will effect all the PCs the network other then just a fixed group of them I mentioned before ?

Any other troubleshooting I should try ? (sorry about the long winded explaination!)
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Question by:BLAZEPOINT
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dathho earned 167 total points
ID: 22725708
Make sure you look to your internal AD/DNS server first(only) from all clients and it forwards requests that it can't answer on to the outside.  If you look first to an outside nameserver for inside resources it will have to timeout for the requests that fail.

Troubleshoot your lookuups with nslookup.

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Author Comment

by:BLAZEPOINT
ID: 22725836
Hi dathho;

Thanks for the quick reponse..I have looked at the Main Domain Controller and and the Alternate DNS entry was indeed set up to an external DNS IP Address (I have only recently taken over the network on this site) I have modified it to point to our second Domain Controller. I will see what happens tomorrow when I return to work and also try nslookups.

Will report back! :-)
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Assisted Solution

by:leegclystvale
leegclystvale earned 167 total points
ID: 22726807
Even if you have removed the external DNS address as the secondary DNS server, you will still need to ensure that your external requests are being forwarded to the right external server.
Check to see what forwarding address/es are set by
Open the DNS admin tool> Select the DNS server to configure>Right-click on the server name> Properties>Forwarders tab>Ensure "All other DNS domains" is selected in the DNS Domain box at the top>Ensure oyu have the extrnal DNS server's IP address for forwarding.
If you can't see any server IP addresses in the forwarders area, you will need to add it. Contact your ISP if unsure what their DNS servers are.
Hope that helps
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Author Comment

by:BLAZEPOINT
ID: 22732571
Hi;
So far I've tried the following; As well as the DNS suggestions above

Edit the Host File with static routes for the Servers. (cleared time out messages in SQL but internet drop outs still occur)

Install Service Pack 3 (This seems to have resolved the issues for the 2 machines I have installed this on (in fact a user who had service pack 3 on his notebook in the office never had any connectivity problems)

Set the network card from Auto neogotaite to fix 100mbps..just awaiting results for that but again problems have disappeared on the ones I have tried.

I will also replace the server switch with a 3com one. I will keep you posted
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Assisted Solution

by:hancke
hancke earned 166 total points
ID: 22805330
Are the effected machines setup on DHCP or static IPs?  Run an IPCONFIG in the CMD prompt to ensure the machines are setup with the correct DNS settings.  They should be setup to DNS to your internal first and then either a secondary internal or your gateway.  If they are setup to DNS to the gateway that would explain the lag in name resolution.  
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Author Closing Comment

by:BLAZEPOINT
ID: 31506500
cSorry so late in reply, the issue was solved by firemoving a rogue router that was plugged in to the network. but all suggestions helped anyhow.
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