[Netkit.users] Speed capacity of virtual interfaces

Massimo Rimondini rimondin at dia.uniroma3.it
Fri May 2 16:00:34 CEST 2008

Dear Julien,

Emilio is right in saying that you wouldn't get much advantage from
using physical/link-layer NIC configuration tools.
The point is that Netkit (or, more precisely, the underlying User-Mode
Linux) provides you with a virtual Ethernet interface that is not bound
to any physical link, thus all the duplex/speed negotiation aspects that
this might bring about are not envisaged. Network performance instead
depends on the capability of the virtual hub to quickly dispatch packets
and this, in turn, depends on the performance of the host machine.

On the other hand, you can still force (typically, limit) some of the
parameters of the virtual links to reproduce more closely the behavior
of a real network. This can be achieved by means of the Netem facility,
which is included in the Netkit kernel. You can find more information
about it by reading the examples at

Another possibility is to replace the standard virtual hub provided with
Netkit with the enhanced vde_switch from the Virtual Distributed
Ethernet project (http://wiki.virtualsquare.org/index.php/VDE). However,
at present Netkit does not provide support to natively configure this
kind of switch.


Emilio Scalise wrote:
> I don't think that mii-tool and ethtool are useful in netkit. Netkit uses UML, 
> user mode linux. You can search on the net about networking in user mode 
> linux for more informations about this topic..
> You can (for example) search on google 'user mode linux network performance', 
> there are many benchmark and comparisons between real machines, uml virtual 
> machines and other types of virtual machine.
> I hope that these informations could be useful for your objectives.
> Bye,
> Emilio
> Il Thursday 01 May 2008 04:35:40 Julien Lange ha scritto:
>> Hello,
>> I'm wondering what are the capacities of the interfaces in netkit. I
>> tried to set up some configuration settings using mii-tool, but it seems
>> that the virtual devices aren't mii compliant. I didn't have any success
>>   with ethtool neither.
>> Can someone tell me a bit more about interface (link) speed setting in
>> netkit? I would like to make some QoS tests, so it would be great to
>> know the default limitation of the link.
>> Thank you very much in advance for your help,
>> Best regards,
>> Julien.
>> _______________________________________________
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>> Netkit.users a list.dia.uniroma3.it
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