I've got some code that does EON tunneling over gif interfaces.  I have
replicated the behavoir as far as I could figure it out from the if_eon.c
code.

The only thing I don't really get is the 4 different address classes
it claims to support: BROADCAST, UNICAST, MULTICAST-ES, and MULTICAST-IS.

The code figures this out by looking at an embedded octet in the route's
gateway (the one after the embedded IP address) which apparently configured
the EON tunnel.

I tested IS-IS on a cisco EON tunnel and it just sets the class to UNICAST
which makes sense (there are no addresses on the encapsulated PDU at least
in the IS-IS case).

Does anyone know anything about these tunnels or when these classes are
really used?

Thanks,
Chris.