problem with designing network modules

[Romain Giry]

Hello,

I'm a french student who is doing his master in Italy and to conclude my 
studies, i
must do a these whose purpose is very close to designing a firewall for 
Linux (i mean).

I should do a module for linux that allows the user to switch the physical 
device
at run-time. In a first time this should be done by user commands and later 
the module
should decide himself to switch the physical device (when for example the 
device is
down or not really effective - the final purpose is to be used under palm 
and different
wireless devices..).
All for all, it's equal to design a new layer between the link and the 
physical layer,
as a firewall does...

My problem is that it's really difficult to find any documentations ( 
especially to know
which functions i should use and by the same time how can i design a 
firewall for
linux) and for the moment i'm reading the linux sources, which is not 
really easy...

That's why i would be very great if anybody can tell me where i can find 
such a
documentation (under the net or in books - i can buy them...) and any 
mailing-list
because it's always very usefull.

Thanks for any comments and if you have any idea of how designing it, i'm 
free to any
remarks and advices,

Romain Giry.
[e-mail] or [e-mail] (prefered)

ps : sorry for my english and i hope i've been enough clear.

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