[Qemu-devel] Connecting two tap interfaces to one qemu instance

[Qemu-devel] Connecting two tap interfaces to one qemu instance

[Jedrzej Kalinowski]

Hello,

I've found a problem when trying to run one qemu instance with two tap
devices connected to a bridge.

I mean a commandline like this:
qemu -net nic -net tap -net nic -net tap ...

After a short time (in seconds, rather than minutes, depends on the
machine I'm runnig qemu) my network gets flooded with packets - mostly
arp requests gathered from all over the network and replicated.

What's interesting there is no problem with running two or more qemu
instances, when giving each one a tap device and connecting all of them
to the same bridge - everything works fine then.

The issue appears on qemu 0.10.5 stable both in FreeBSD and Linux
environment.

Have any of you tried to use two tap devices in one qemu instance? Any
luck?



Any information would be greatly appreciated,
Jedrzej Kalinowski

Re: [Qemu-devel] Connecting two tap interfaces to one qemu instance

[Brian Jackson]

Try turning STP on for the bridge maybe.


On May 28, 2009, at 3:23 PM, Jedrzej Kalinowski wrote:

> Hello,
>
> I've found a problem when trying to run one qemu instance with two tap
> devices connected to a bridge.
>
> I mean a commandline like this:
> qemu -net nic -net tap -net nic -net tap ...
>
> After a short time (in seconds, rather than minutes, depends on the
> machine I'm runnig qemu) my network gets flooded with packets - mostly
> arp requests gathered from all over the network and replicated.
>
> What's interesting there is no problem with running two or more qemu
> instances, when giving each one a tap device and connecting all of  
> them
> to the same bridge - everything works fine then.
>
> The issue appears on qemu 0.10.5 stable both in FreeBSD and Linux
> environment.
>
> Have any of you tried to use two tap devices in one qemu instance? Any
> luck?
>
>
>
> Any information would be greatly appreciated,
> Jedrzej Kalinowski
>
>

Re: [Qemu-devel] Connecting two tap interfaces to one qemu instance

[Jedrzej Kalinowski]

Brian Jackson pisze:
> Try turning STP on for the bridge maybe.
> 
> 
> On May 28, 2009, at 3:23 PM, Jedrzej Kalinowski wrote:
> 
>> Hello,
>>
>> I've found a problem when trying to run one qemu instance with two tap
>> devices connected to a bridge.
>>
>> I mean a commandline like this:
>> qemu -net nic -net tap -net nic -net tap ...
>>
>> After a short time (in seconds, rather than minutes, depends on the
>> machine I'm runnig qemu) my network gets flooded with packets - mostly
>> arp requests gathered from all over the network and replicated.
>>
>> What's interesting there is no problem with running two or more qemu
>> instances, when giving each one a tap device and connecting all of them
>> to the same bridge - everything works fine then.
>>
>> The issue appears on qemu 0.10.5 stable both in FreeBSD and Linux
>> environment.
>>
>> Have any of you tried to use two tap devices in one qemu instance? Any
>> luck?
>>
>>
>>
>> Any information would be greatly appreciated,
>> Jedrzej Kalinowski
>>
>>
> 

Yes, I tried STP on bridge and it helps.
But it's fighting effects, not cause of the problem

My understanding is that qemu should not work like this. Usual host with
two network devices connected to the same network doesn't create loops
like this.

--
Jedrzej Kalinowski

Re: [Qemu-devel] Connecting two tap interfaces to one qemu instance

[Paul Brook]

> Yes, I tried STP on bridge and it helps.
> But it's fighting effects, not cause of the problem
>
> My understanding is that qemu should not work like this. Usual host with
> two network devices connected to the same network doesn't create loops
> like this.

You aren't emulating a host with two devices. You're emulating a switch with 
three ports. One connected to the guest, and the other two connected to tap 
interfaces. Exactly the same thing will happen if you implement this topology 
with real hardware.

Paul

[Qemu-devel] Re: Connecting two tap interfaces to one qemu instance

[Charles Duffy]

Jedrzej Kalinowski wrote:
> Hello,
> 
> I've found a problem when trying to run one qemu instance with two tap
> devices connected to a bridge.
> 
> I mean a commandline like this:
> qemu -net nic -net tap -net nic -net tap ...

Do this instead:

qemu -net nic,vlan=0 -net tap,vlan=0 -net nic,vlan=1 -net tap,vlan=1 ...

Re: [Qemu-devel] Re: Connecting two tap interfaces to one qemu instance

[Jedrzej Kalinowski]

Charles Duffy wrote:
> Jedrzej Kalinowski wrote:
>> Hello,
>>
>> I've found a problem when trying to run one qemu instance with two tap
>> devices connected to a bridge.
>>
>> I mean a commandline like this:
>> qemu -net nic -net tap -net nic -net tap ...
> 
> Do this instead:
> 
> qemu -net nic,vlan=0 -net tap,vlan=0 -net nic,vlan=1 -net tap,vlan=1 ...
> 
> 
> 

It helped, thank you!

-- 
Jędrzej Kalinowski