4.2 TCP/IP/Ethernet trailers

[Bill Shannon]

Philisophically, I don't believe there is anything wrong with the
4.2 TCP/IP Ethernet code, it simply imposes another software layer
(the local net encapsulation) between IP and the Ethernet.
Practically, I think it is rather unfortunate since it destroys
compatibility with the "obvious" implementations of IP on Ethernet.
Having some way of negotiating for the use of trailers sounds nice
but it also sounds like another software layer which won't be
present in the "obvious" implementations.  The same sort of problem
exists with ARP.  Perhaps what is needed is a "standard" for how
to implement IP on Ethernet.

In the Sun 4.2 system we've made it easy to turn off trailers in the
driver, however ARP is mandatory.  We may provide a way to "wire down"
ARP translations (however the ARP translation table is by nature a
cache and therefore small) and I guess it would also be possible
to enable trailers based on the destination address.  As we start
talking to other TCP/IP/Ethernet implementations I suspect we will
have to address these problems more directly.

					Bill Shannon
					sun!shannon
					Sun Microsystems, Inc.