NIT putmsg problem

[Sean Holdsworth]

I'm currently trying to use the NIT interface to the ethernet. Whilst I've
got the receiving side working without too much pain, I'm beginning to
have doubts about whether what I'm trying to do on the send side is
possible.

What I want to be able to do is to build and send ethernet packets.  I'd
hoped to be able to assign my own ethernet packet type in the same way as
IP, ARP, RARP et al. do. I can see that this could cause problems on the
receive side but I can't even get the packet onto the net.

My approach is to build a message out of a control part comprising the
destination address; a sockaddr structure with sa_family set to AF_UNSPEC
and with the sa_data being the ethernet header. I then build a data part
comprising the same ethernet header concatenated with the actual data.
The message is then sent down the nit stream using putmsg.

Am I doing something obviously wrong? Are there any known bugs which might
be biting me? I'm running SUNOS 4.1 on a Sparc station using the le0
interface. One anomaly I have come across is the manual page description
of the write side behaviour of the nit_if module; if I read it correctly
it implies that if the data part of the message does not start with an
ethernet header then an error will be signalled back up the stream and
this does not seem to be happening...

Any help will be much appreciated especially if someone could send me some
working source code of a toy example.

                             Sean Holdsworth.
   UUCP:  ...!uunet!mcsun!ukc!man.cs!seanh          Fax: +44-61-275-6236
   Inet:  seanh%cs.man.ac.uk at nsfnet-relay.ac.uk     Int: 6294