> 1. Is io-pkt's  version of QNET compatible with 
> io-net's implementation of  this protocol? 

Absolutely!  What goes out on the wire is the
same in both cases.  io-net and io-pkt are just
different drivers, from qnet's hardware-independent
perspective.
 
> 2. ... I  will create own network sniffer ... we 
> need to know packet structure of L3, L4 of 
> QNET protocol to make this. 

No problem!  All of the header files are included
with the source - have you downloaded it yet?
It's in the sys/lsm/qnet directory.  Everything
you should need is there - header files with
packet header definitions, resolver packets,
connection establishment, data transfer and
re-assembly, etc.
 
> 3. Using simple sniffing of Ethernet I found 
> that data is send over the line in open form 
> is it a way to make safe communication (by 
> encryption for example) between our devices/nodes 
> without changing of message passing principals we 
> have. So, ideally encryption/decryption should 
> happens inside of QNET stack transparently for 
> IPC. In io-net it can be done by implementing specific 
> filter module but is it possible in io-pkt?

Hm.  One very simple way to do this (no source
mods) it to use bind=ip and ipsec.  

If you don't like that (eg performance) then another 
easy way is to do it in your driver, so your driver takes
the unencrypted data from qnet, encrypts it,
transmits it over the wife, and on the other
end your driver receives the encrypted data,
decrypts it, and passes it up to qnet.

Of course, since you have the source to qnet,
you could add an encryption layer to it, so that
it passed the encrypted data to the stock
driver.

There are a LOT of ways to solve this.  I've
probably missed some  :-)