trivial DNS issues

trivial DNS issues

[Cristi Magherusan]

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Hello,

It seems that qemu (and our kvm-qemu branch) and virtualbox suffer of
this issue regarding the DNS resolver:
http://www.virtualbox.org/ticket/421

I know it's mostly a DHCP client config problem, but we could try if the
designated DNS servers are reachable before we pass them to our virtual
machine, instead of blindly passing the first one.

Best regards,
Cristi

-- 
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro

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Re: trivial DNS issues

[Avi Kivity]

(copying qemu-devel)


Cristi Magherusan wrote:
> Hello,
>
> It seems that qemu (and our kvm-qemu branch) and virtualbox suffer of
> this issue regarding the DNS resolver:
> http://www.virtualbox.org/ticket/421
>
> I know it's mostly a DHCP client config problem, but we could try if the
> designated DNS servers are reachable before we pass them to our virtual
> machine, instead of blindly passing the first one.
>   

What does your /etc/resolv.conf look like?



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Re: trivial DNS issues

[Cristi Magherusan]

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Hello,

On Mon, 2008-09-01 at 13:29 +0300, Avi Kivity wrote:
> What does your /etc/resolv.conf look like?
It used to look like this:

nameserver 127.0.0.1
nameserver <PRIMARY_DNS_IP>
nameserver <SECONDARY_DNS_IP>

Inside the VM the DNS resolver was broken.
After removing that line from the dhclient config now I have only my
real DNS servers, and DNS works inside the VM.

Those who have installed a local DNS server may need that stuff, but we
can check every entries of resolv.conf and see if we can connect to
their DNS server, and use in our VM the first one that could be reached.

Thanks,
Cristi

-- 
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro

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Re: trivial DNS issues

[Avi Kivity]

Cristi Magherusan wrote:
> Those who have installed a local DNS server may need that stuff, but we
> can check every entries of resolv.conf and see if we can connect to
> their DNS server, and use in our VM the first one that could be reached.
>
>   

The network maybe down when the VM is started, or the dns server may be 
down, or ...

Maybe we should forward the host's dns servers to the guest, replacing 
127.0.0.1 by 10.0.2.2.

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Re: trivial DNS issues

[Cristi Magherusan]

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On Mon, 2008-09-01 at 14:14 +0300, Avi Kivity wrote:
> Cristi Magherusan wrote:
> > Those who have installed a local DNS server may need that stuff, but we
> > can check every entries of resolv.conf and see if we can connect to
> > their DNS server, and use in our VM the first one that could be reached.
> >
> >   
> 
> The network maybe down when the VM is started, or the dns server may be 
> down, or ...
> Maybe we should forward the host's dns servers to the guest, replacing 
> 127.0.0.1 by 10.0.2.2.
Then we should forward them all, but the localhost one should be tested
and skipped if unavailable.

Cristi

-- 
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro

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Re: trivial DNS issues

[Avi Kivity]

Cristi Magherusan wrote:
> On Mon, 2008-09-01 at 14:14 +0300, Avi Kivity wrote:
>   
>> Cristi Magherusan wrote:
>>     
>>> Those who have installed a local DNS server may need that stuff, but we
>>> can check every entries of resolv.conf and see if we can connect to
>>> their DNS server, and use in our VM the first one that could be reached.
>>>
>>>   
>>>       
>> The network maybe down when the VM is started, or the dns server may be 
>> down, or ...
>> Maybe we should forward the host's dns servers to the guest, replacing 
>> 127.0.0.1 by 10.0.2.2.
>>     
> Then we should forward them all, but the localhost one should be tested
> and skipped if unavailable.
>   

Why?  A local application will have exactly the same problems with a 
broken dns server on localhost, as a virtual machine with that address 
forwarded.  And if the the dns server is later fixed, both the local 
application and the guest will recover.

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Re: trivial DNS issues

[Cristi Magherusan]

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On Mon, 2008-09-01 at 15:37 +0300, Avi Kivity wrote:
> Why?  A local application will have exactly the same problems with a 
> broken dns server on localhost, as a virtual machine with that address 
> forwarded.  And if the the dns server is later fixed, both the local 
> application and the guest will recover.

Okay, then maybe we should just pass them all to the VM and replace
localhost's address, if present, with the internal gateway just like you
said before.

Cristi

-- 
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro

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