[Ns-developers] How to tap an NetDevice into another one ?

[Tom Henderson]

On 11/16/2011 03:20 PM, Tommaso Pecorella wrote:
> Hi all,
>
> request for suggestions (maybe I missed something).
>
> I want to stick an NetDevice on top of another one, masquerading it in
> the "right" way. So far I borrowed the idea from the Bridge interface,
> but I'm far from happy about the results.
>
> Let me first explain the problem better.
>
>       Normal stack           Custom stack
>    +------------------+  +--------------------+
>    |  IP layer        |  |  IP layer          |
>    |                  |  +--------------------+
>    +------------------+  |  ghost layer       |
>    |  MAC layer       |  +--------------------+
>    |                  |  |  MAC layer         |
>    +------------------+  +--------------------+
>
> The problem with the approach I used is that it works BUT I have one
> extra NetDevice in the list of the node devices, so a dumb code could
> try to use it, while it should be invisible but for the ones explicitly
> checking for it.
>
> Any smart ideas ?

Are there particular problems with existing code getting confused?  I 
think it is probably a job of the upper-layer code to be smarter about 
which devices to use or not.  For example, IPv4 global routing code will 
not try to use net devices that do not have a corresponding IPv4 
interface defined.

>
> BTW, if you're wondering the ghost layer is basically shrinking IP
> packet headers, as is, it's the 6LoWPAN layer. I was even thinking to
> add it to the IP stack as a decorator, but it's a bit an overkill... or
> not ?

I was thinking that 6LoWPAN could be instead supported by a single 
NetDevice that combined 802.15.4 mac and phy with the 802.2 LLC and 
convergence layers specific to 6LoWPAN.  Does your 6LoWPAN layer have to 
be another NetDevice?

- Tom