>"DECNET nodes change their ethernet address when DECNET comes up. The
> trailing bits identify the decnet node."
>Um, there is at least one PC Ethernet controller that allows the user
>to reprogram the machine's Ethernet ID.
I'm usually just lurking here trying to learn something but at last here's
something I know about...
We run a large DECnet shop with around 500 pcs with ethernet boards from dozens
of manufacturers. I've yet to see a pc ethernet board that does NOT allow the
address used on the wire to be reprogrammed.
>One presumes that one can reset the entire ethernet number, not just the
>lower half. May as well have an eraseable manufacturer's name, part number,
>and serial number, IMHO.
In fact it is entirely reprogrammed - the first part is always aa-00-04-00 and
the last two octets give the decnet area and address.
>To summarize : if you have PCs on your ethernet, there exists a nontrivial
>possibility of you being spoofed and having a hell of time finding the
>system causing the problem ( short of a subnet-by-subnet search, thence
>an office-by-office search, as surely many on this list have engaged in
>over the years, a sort of Easter Egg Hunt for adults ... :-)
Non-trivial is right! It's bad enough when two stations come up with the same
DECnet address and they're close to each other but if there happens to be a
bridge between them, the bridge sees the two addresses as probably meaning
there's a loop in the lan and shuts down at least long enough to renegotiate
the spanning tree. Our usual procedure os to shut down the node that is
supposed to be using the address, then look at filter tables on bridges to
discover which building the imposter is in. Then comes the segment-by-segment
followed by office-by-office search. Maybe your egg hunt comment will allow me
to chuckle a bit (between teeth gnashing sessions) next time...
As to the original question, aa-00-03 is an ethernet address I've come across
on DEC DEUNA devices which may help narrow the search a bit.
conni annable network manager
University of Texas Health Science Center at San Antonio
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