When using host resolver, VirtualBox forwards a PTR query as an A query

How do you rule out this being VirtualBox's fault?

Hi Thomas,

Because when I disable dnsmasq from NetworkManager config, and I get the my regular DNS server into resolv.conf (of my host), the Virtualbox guests behave normal.

so I thought if the issue occurs with dnsmasq, and doesn't occur without it, then it's dnsmasq's fault and not Virtualbox (which can't really know if dnsmasq is even used or not).

Hi Thomas,

This is indeed not a dnsmasq issue.

It is Virtualbox, turning PTR queries into A queries when the name server on the host's resolv.conf file is from 127.0.0.0/8 segment.

I'm still investigating why.

Hi Bar,

I can reproduce the behavior: Debian 7 in VM with NATted network interface on VirtualBox 4.2.16 on Ubuntu 13.04 with the NetworkManager-controlled dnsmasq instance running. Using wireshark on the host I see 127.0.1.1 receiving an A query instead of a PTR query.

Hi Thomas.

Good to hear you can reproduce it.

Anything else I need to do?

Sorry for the double-post.

I believe this is the code that is causing Virtualbox to behave like this:
https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Devices/Network/slirp/slirp_dns.c#L283

I don't have any idea why it is there, but it says that it's specifically for "modern" Ubuntu releases which have 127.0.1.1 as the name server (Network-Manager-managed dnsmasq...)

Thanks!
Bar.

It looks to me as if the purpose of that code is to detect the host DNS configuration. The section labeled with the comment "Modern Ubuntu register 127.0.1.1 as DNS server" seems to be executed in case a loopback address other than the classic 127.0.0.1 is found on a "nameserver <ipaddr>" line in resolv.conf — which is the case in Ubuntu 12.10 and later — and the important thing for us is that it sets fUseHostResolver = 1.

I guess we need to look at the code that is activated by fUseHostResolver == 1.