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trivial DNS issues

DISCUSSION Cristi Magherusan 2 participants 7 messages Sep 1, 2008 KVM

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#0 lore raw

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

Signature · 4 lines
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro
#1 lore raw

(copying qemu-devel)

Quoted 10 lines · Cristi Magherusan

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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error compiling committee.c: too many arguments to function
#2 lore raw

Hello,

Quoted 1 line · Avi Kivity

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

Signature · 4 lines
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro
#3 lore raw
Quoted 5 lines · Cristi Magherusan

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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error compiling committee.c: too many arguments to function
#4 lore raw
Quoted 11 lines · Avi Kivity
Quoted 5 lines · Cristi Magherusan

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

Signature · 4 lines
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro
#5 lore raw
Quoted 10 lines · Cristi Magherusan
Quoted 8 lines · Avi Kivity
Quoted 6 lines · Cristi Magherusan

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.

Quoted 6 lines
Quoted 3 lines

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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error compiling committee.c: too many arguments to function
#6 lore raw
Quoted 4 lines · Avi Kivity

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

Signature · 4 lines
Ing. Cristi Măgherușan,
Universitatea Tehnică din Cluj-Napoca
Centrul de Comunicații "Pusztai Kalman"
Tel. 0264/401247  http://cc.utcluj.ro