interprocess communication with netlinks

Hi netdev gurus !

I am trying to make several processes to communicate via the netlink 
protocol.

I saw a discussion around the AF_IPN (inter process communication) 
protocol and it seems the same can be done with the AF_NETLINK protocol 
with minor modifications in the kernel. Were these modifications done ?

I am trying to use multicast between several processes, for notification.

What protocol should I use to create the socket ?

    fd = socket(PF_NETLINK, SOCK_RAW,  ???);

I was not able to find any suitable pointer to explain how to do that, 
so I blindly tried several combinations but I am afraid to interact with 
the other netlink protocols when using a multicast group, especially 
when there are other applications like avahi-daemon or "ip monitor all".

Does anyone have a pointer to a documentation (not the redhat one, pls), 
or some clues ?

Thanks in advance.
  -- Daniel