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I have a CentOS 6 x86 server. If I ping and my server gateway, there's no problem. If I ping,, etc, it returns "ping: unknown host".

When I saw this problem, first thing I go to check is the /etc/resolv.conf file, but this file seems no problem. Where else should I check?

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The second nameserver should probably be – Raffael Luthiger Dec 12 '11 at 13:21
Nop, is not working anymore. – Dr I Dec 12 '11 at 13:24
@DrI: Good to know. It is a long time ago I had to use them the last time. – Raffael Luthiger Dec 12 '11 at 16:31

3 Answers 3

Few things you can try

Look at


Look for hosts: and see if it has dns listed

Then try to query from their nameservers.. maybe output dns requests are failing


If that fails.. then

telnet 53

If you get a connection refused.. your ISP might be blocking your dns requests and you have to use their resolvers.

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Do you maybe have a firewall in between which is blocking DNS traffic? You can try to make a lookup with dig and see if it works or not:

dig @

If this does not work then it is probably a device (firewall) in between which is blocking your DNS traffic.

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It seems that you don't have internet access at all, don't you?

If this is the case, have a look at your routing table using command route.

If you don't see a line like this one:


you probably have a gateway problem, check your network settings.

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He sais that he can ping so he has internet access for sure. – Raffael Luthiger Dec 12 '11 at 13:26
My bad, I didn't noticed that this ip was public google dns. I thought this was the ip for his router. They have a troubleshooting page here, maybe it will help. link – Yann Sagon Dec 12 '11 at 13:50

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