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To:	ARISIA::EVERHART
Subj:	Re: delua vs. deuna vs. third party


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Date: 16 Jul 88 19:50:01 GMT
From: agate!helios.ee.lbl.gov!ace.ee.lbl.gov!leres@ucbvax.Berkeley.EDU  (Craig Leres)
Organization: Lawrence Berkeley Laboratory, Berkeley
Subject: Re: delua vs. deuna vs. third party
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Ed Wilts writes:

>DEC cheats in their DECnet code and will only store the trailing 3 parts
>(6 digits) of an Ethernet address.  For example, if your ethernet address
>is "08-00-36-e9-1e-00", DEC only uses "e9-1e-00".  This is because the first
>3 parts are reserved to the manufacturer.  We have a third party Ethernet

This turns out not to be the case. Dec ethernet interfaces are like
other manufacturers in that each board has a unique ethernet address.
The block assigned to dec for unibus and qbus machines is 8:0:2b:?:?:?.
So if you have an Vax running Berkeley Unix on it with a deuna, deqna,
or delua on it, then its ethernet address will start with 8:0:2b.

On the other hand, decnet requires stations use a "logical address"
that is based on the node and area numbers. The block assigned to dec
for this purpose is aa:0:4:?:?:?. So if you have a machine running
decnet on ethernet, its ethernet address with start with aa:0:4 and
will end with three octets determined by your node and area numbers.
Unfortunatly, I don't have the calculation handy, but I think it works
like this: the 4th octet is always zero, the 5th octet is the node
number and the 6th octet is the area number shifted left 2 bits. So
node 1 in area 1 is aa:0:4:0:1:4.

Note that the only reason it's possible to change the hardware ethernet
address is because dec wanted/needed this feature for decnet and they
were one of the companies who drew up the ethernet specification.

>                                           We have a third party Ethernet
>controller made by Intergraph Corp., and it will NOT run DECnet.  DEC assumes

The reason you can't run decnet on your ethernet interface is not
because decnet doesn't support it but because VMS doesn't support it.
If you wrote a vax/vms device driver for your board which supported the
"alt start" internal interface, it should be possible to run decnet on
it.

>                                                                  DEC assumes
>that they know the first 3 parts because they have them reserved.  In our

As I explain above, they assume they know the first three octets
because the protocol (stupidly) requires it.

Getting back to the original question, if you want to run decnet, then
you're better off buying a dec ethernet interface; writing a vax/vms
driver that supports decnet is not a trivial job. (The deuna driver is
something like 2000 or 3000 lines of assembler.)

But if you want to run tcp/ip only (using one of the Wollongong or
Multinet packages) and don't care about decnet, then you can buy nearly
any interface that is supported by BSD Unix.

		Craig