[Ns-developers] VirtualNetDevice (TUN/TAP)

[Gustavo Carneiro]

On 25/05/2008, Mathieu Lacage <mathieu.lacage at sophia.inria.fr> wrote:
>
> On Sun, 2008-05-25 at 17:12 +0100, Gustavo Carneiro wrote:
>
> >         My first reaction is that I would have expected the packet
> >         encapsulation to be part of the VirtualNetDevice class and to
> >         not be
> >         delegated to the application.
> >
> > This is exactly what is done by TAP interfaces; userspace just
> > receives a packet to be sent, from the IP stack, and this is where the
> > job of the TAP interface ends on the TX path.  This model is simple
> > and flexible, as it allows you to do more than tunneling, and allows
> > to do tunneling in anyway you want.
>
>
> I see. What is the interface between the TAP interface and the
> application on linux ? Does it open a special socket for reading and
> writing ?


Exactly.

>         If I am not totally wrong, the
> >         decapsulation at the other side of the connection also needs
> >         to be done
> >         by a VirtualNetDevice and a matching application ? If so, it
> >         really
> >         seems to me that supporting a VirtualChannel would make a lot
> >         of sense
> >         because the two VirtualNetDevice (tx and rx) and indeed
> >         connected.
> >
> > The way I am using is roughly like this (it's more complicated,
> > but...):
> >
> > On the transmitter node:
> >
> > Application -> UdpSocket1 -> IPv4 -> VirtualNetDevice -> Tunneling
> > Code -> UdpSocket2 -> IPv4 -> PointToPointNetDevice ...........
> >
> > On the receiver node:
> >
> > ---> WifiNetDevice -> IPv4 -> UdpSocket3 -> Tunneling Code ->
> > VirtualNetDevice -> IPv4 -> UdpSocket4 -> SinkApp
> >
> > Fun, isn't it? :-)
>
>
> I see.
>
>
> > Anyway, I don't think adding a VirtualChannel to this picture helps.
>
>
> Maybe it does not help your specific use-case but the API was designed
> to be implemented that way and, since there is nothing in your use-case
> which makes this impossible, it would make sense to attempt to implement
> the API fully.


I wouldn't know what to do with a VirtualChannel or what that channel would
do in this case.

-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert