Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!gdt!exspes
From: exspes@gdr.bath.ac.uk (P E Smee)
Newsgroups: comp.sys.dec
Subject: Re: DECNET MAC address use query
Message-ID: <1990Nov12.155501.23342@gdr.bath.ac.uk>
Date: 12 Nov 90 15:55:01 GMT
References: <1990Nov8.125106.18326@gdr.bath.ac.uk> <12925@blia.BLI.COM>
Reply-To: P.Smee@bristol.ac.uk (Paul Smee)
Organization: University of Bristol c/o University of Bath
Lines: 37

In article <12925@blia.BLI.COM> ted@blia.BLI.COM (Ted Marshall) writes:
>In article <1990Nov8.125106.18326@gdr.bath.ac.uk>, exspes@gdr.bath.ac.uk (P E Smee) writes:
>> We are told that DEC, rather than assigning a single MAC address to a
>> given machine, assigns a group of MAC address to each box, so that the
>> DECNET protocol can use some of the 'address' bits to send small
>> control messages around.  (I find this distasteful, but apparently it's
>> 'legal' as long as they stick to their assigned address range.)
>
>Whomever told you that is dead wrong! A machine running DECnet has its
>Ethernet address set based on the DECnet address (see below). Each machine
>has a single address only. Multicast addresses in the range AB-00... are
>also used but not as station addresses.
>
>The station address is set as follows: The first 4 bytes are AA-00-04-00.
>The last two bytes are computed as (area * 1024 + node), byte swapped.
>Thus, DECnet address 8.56 would compute as (8 * 1024 + 56) = 8248 = 0x2038.
>Thus, the corresponding Ethernet address would be AA-00-04-00-38-20.

How about the following as a closer guess?  We are running a number of
DEC machines with hardware MAC addresses of 08-00-2b-... (and a Silicon
Graphics box 08-00-69-...).  We are told that when they start wanting
to use DECnet across our bridges, we will have to tell the bridges that
their addresses are AA-00-04-<something else>.  It appears that this
latter address holds when they are running DECNET protocol; and we
believe that they will still continue to claim to be 08-00-2b-whatever
when they are running other protocols.  Is this any better?  (Still
means that from the point of view of the bridge, the box has two
addresses.)

We also hear rumours that AA-00-04-... machines may under some
circumstances use AA-00-03-<same thing>.  (AA-00-03-... is registered
as 'Global physical address for some DEC machines' -- or, in other
words, is assigned to DEC.)

-- 
Paul Smee, Computing Service, University of Bristol, Bristol BS8 1UD, UK
 P.Smee@bristol.ac.uk - ..!uunet!ukc!bsmail!p.smee - Tel +44 272 303132