Network Traffic Generation

[Shachar Shemesh]

Oleg Goldshmidt wrote:

>
>   
>> It is, indeed, worth a try.
>>     
>
> If you do, I am curious whether it works or not, so a summary will be
> appreciated.
>   
Me it'll take some time until I get to try it. If Daniel tries it, 
please do report.
>   
>> Switching is fine, as long as they are only layer 2 aware. So long
>> as you actually have two actual physical network cards, there is no
>> reason for the packet not to go out. A layer 3 switch might notice
>> the short path, but a layer 2 switch should work fine.
>>     
>
> Unless VM0 sends an ARP inquiring about the destination IP,
This ARP is sent to a physical NIC.
>  VM1
> dutifully replies with its MAC (all through the hypervisor's virtual
> switch),
No, as far as the machine is concerned, the sending out of an ARP 
through VM1 and receiving it through VM0 are two separate events. Unless 
it is layer 3 aware, there is no reason for it to know that the ARP 
received through a physical Ethernet device originated in our machine.
>  then VM0 stack forms a frame with VM1's MAC as destination.
>   
Of course it does. I find it hard to believe that a VM would form a 
switch between two separate physical interfaces. In fact, VMs work extra 
hard to make sure that you can INCREASE the number of physical layers 
you have, no decrease it.
> The frame, from VM0's point of view, goes out of its *virtual* NIC,
> and then gets L2-switched locally by the virtual switch without going
> out of any physical interface.
>   
Who gave the VM the right to assume that VM1 and VM0 are layer 2 
connected? If it does that, switch VM software - it's a bug.

Shachar


-- 
Shachar Shemesh
Lingnu Open Source Consulting Ltd.
http://www.lingnu.com

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