[Nix-dev] kernel 3.6 NAT issues

[Mathijs Kwik]

Just to close this thread:

It's fixed in kernel 3.6.2 now.


On Thu, Oct 11, 2012 at 1:52 AM, Mathijs Kwik <mathijs at bluescreen303.nl> wrote:
> Ok, I tracked it down a bit further.
>
> It seems that doing anything to any interface fixes the problem.
> In my case, I have tap1, which is just a virtual device, connected to
> a qemu/kvm instance. It is setup during boot and given a static ip
> address.
> My connected real interface is wlan0.
> I also have eth0, but no cable is in there so it's not in use in any way.
> When I first boot the kvm instance, it does not have a working
> connection, which I traced down to nat not functioning, as described
> in my original message.
> Now the weird part: if I run:
> ifconfig eth0 down && ifconfig eth0 up
> things start working for the guest. This is weird, because eth0 does
> not even have a cable connected to anything.
> bringing down/up any other interface (lo, wlan0, tap1) all have this effect.
>
> I tried to find out what changes by doing this, but both my
> "iptables-save" as "ip route" outputs stay the same.
> It seems something gets cached/broken, and doing anything to any
> interface just triggers something to reload/release caches.
> And as stated, this only happens on 3.6.*, I tried 3.5.6 too just now,
> where everything works as it should.
>
> Now, after restarting qemu/kvm, the same problem shows up again so
> clearly its startup corrupts something.
> This is somewhat weird again, as kvm fully runs as a normal user. The
> tap1 device it uses is setup beforehand (system boot) and is owned by
> the normal user, so that running the vm does not require any root
> access.
>
> As a simple workaround, I thought of just addinf the down/up step for
> eth0(which I never use) into my start-vm script, but as ifconfig needs
> root access, it really becomes a dirty hack.
>
> Does anyone have a clue what might be causing this?
>
> On Thu, Oct 11, 2012 at 12:25 AM, Mathijs Kwik <mathijs at bluescreen303.nl> wrote:
>> On Wed, Oct 10, 2012 at 7:41 PM, Lluís Batlle i Rossell
>> <viric at viric.name> wrote:
>>> On Wed, Oct 10, 2012 at 07:21:30PM +0200, Mathijs Kwik wrote:
>>>> I'm trying out kernel 3.6 at the moment and all is well except for 1 thing.
>>>> NAT / masquerading does no longer seem to work.
>>>
>>> No idea; maybe a try on 3.6.1?
>>
>> I'm on 3.6.1 :)
>> But the issue first appeared on 3.6.
>>
>> It's getting even weirder though. If I suspend my system (to ram) and
>> wake it up, it's fixed.
>> But that's at least a lead to investigate further.
>>
>> I should probably just quit my bleeding-edge habit, but that's another thing :)