tun.c non formal header protocol?

tun.c non formal header protocol?

[Kfir Lavi]

Hi,
I would like to use custom protocol over tun/tap device.
I'm grabbing packets, and changing them, to deliver via tap,
to a listener that knows this custom protocol.
The custom protocol is just wrapping the packet with another
small header.
Is it possible to move custom packets via tun.c ?
Is it possible to have a hook, just before the receiver gets
the packet, and then modify the header of the packet, so
it will not disturb tun.c ?

Is there any other options having the power of Linux stack
and netfilter, and using this custom protocol.

I'm grabbing the packets to userspace using nfq, and then with
verdict I'm returning them to the tap device.

Thanks,
Kfir

Re: tun.c non formal header protocol?

[Rémi Denis-Courmont]

Le jeudi 24 février 2011 20:37:32 Kfir Lavi, vous avez écrit :
> I would like to use custom protocol over tun/tap device.

Over TAP, you can only exchange Ethernet frames. However you can use whatever 
network layer you like (so long as it has an Ethernet type associated).

Over TUN, you can exchange packets without any link layer header, for any 
network layer protocol defined in Linux.

In principles, you can probably just use a (Ethernet) type that is not used by 
any existing stack in the Linux kernel. But I don't see any point in doing so, 
as the kernel will just drop the packets on the floor afterward.

> I'm grabbing packets, and changing them, to deliver via tap,
> to a listener that knows this custom protocol.
> The custom protocol is just wrapping the packet with another
> small header.
> Is it possible to move custom packets via tun.c ?

It's difficult to say without a clearer picture what you are trying to do.

-- 
Rémi Denis-Courmont
http://www.remlab.info/
http://fi.linkedin.com/in/remidenis