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Ubuntu Server Won't Resolve Hostnames

Posted on 2014-02-18
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Last Modified: 2014-02-20
Just installed a fresh build of Ubuntu Server 12.04.4 x64 to find that I can't get DNS functionality to work.  In the configuration wizard, I entered the name server of 8.8.8.8.  I can successfully ping this IP and can see its entry in /etc/resolv.conf and /etc/network/interfaces.  But I can't perform nslookup or ping any hostname.
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Question by:marrj
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Expert Comment

by:Mazdajai
ID: 39868788
Is iptables running? What is your network configuration?
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by:marrj
ID: 39868799
I'm fairly new to Linux.  How do I tell if iptables is running?

By network configuration, do you mean the content of the /etc/network/interfaces file?
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by:Tintin
ID: 39868845
What's the output of

iptables -L
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Expert Comment

by:Mazdajai
ID: 39869167
Yes. Beside iptables provide the following -

dig google.com 8.8.8.8

Open in new window

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Expert Comment

by:Sandy
ID: 39869615
Also check with your network guy whether port 53 is open or not to allow name resolution.

TY/SA
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Expert Comment

by:Surrano
ID: 39870223
Instead of asking to open port 53 I'd recommend to ask your network team to give you a proper DNS IP within the intranet. Tends to be more friendly and less prone to future nasty comments from network team :)
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by:marrj
ID: 39870284
Output from iptables -L

Chain INPUT (policy ACCEPT)
target     prot opt source     destination

Chain FORWARD (policy ACCEPT)
target     prot opt source     destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source     destination




Output from dig google.com 8.8.8.8

;; global options: +cmd
;; connection timed out; no servers could be reached
;; connection timed out; no servers could be reached



I happen to the be the network guy, and I am certain that outbound TCP53 is open at my ASA.  This server is going to be in a DMZ, and I really don't want to open up anything from the DMZ to the inside that I don't have to.  I've also got a static NAT created at my ASA for this machine.  As I said, I can ping any IP (public or private) that I want to.  I just can't perform name lookups.  I don't think it's a NAT or port issue.  I've got a Windows server set up the same way and have no problems performing nslookup on 8.8.8.8.
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Assisted Solution

by:Tintin
Tintin earned 250 total points
ID: 39871782
Make sure you have UDP 53 opened on the ASA.   Most DNS queries are over UDP rather than TCP.
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Mazdajai earned 250 total points
ID: 39872322
>>I've got a Windows server set up the same way and have no problems performing nslookup on 8.8.8.8.

Can you confirm the Ubuntu server and the Windows are in the same subnet? As well as UDP53 is open?
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by:marrj
ID: 39873884
I decided to reinstall the OS from scratch.  Now, DNS works fine.  Strange.  Thanks for your help.
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