On Tue, 29 Feb 2000, Bert Driehuis wrote:
> On Mon, 28 Feb 2000, Guy Harris wrote:
> > Well, the first thing you'd need for a LAT decoder would be a
> > specification of the LAT protocol...
> >
> > ...unfortunately, DEC have never published it.
> >
> > In fact, the LBL version of tcpdump *doesn't* understand LAT - all it
> > does is hand off packets with an Ethertype of ETHERTYPE_LAT to the
> > default printer.
>
> Well, reverse engineered implementations do exist, as I seem to remember
> one company forced to take a license as a result of legal action
> (TSSnet?).
Meridian is probably still making money off their license, and if they are
then so is Compaq. Don't stir up a nest of lawyers unless you are ready
to face them.
> > DECNet, on the other hand, is documented; see
> >
> > http://gatekeeper.dec.com/pub/DEC/DECnet/PhaseIV/
>
> And fun to do as well :-) Forget PhaseV though. I don't think any
> customer of DEC got their network converted before TCP/IP took over.
Dunno about converted, but I ran Phase V happily for several years until
they took my VMS systems away.
> As an easy first start, decoding the Ethernet address of a DECnet host
> into a node number would be fun.
Trivial. The MAC address is aa-00-04-00-NN-NN. (NNNN >> 10) is the area
number and (NNNN & 0x3ff) is the node number. I don't recall whether the
bytes in NNNN have to be swapped first -- I wrote a DCL script to remember
this stuff for me. The result is expressed in decimal as
areanumber.nodenumber .
DECnet through Phase IV has the equivalent of host tables, squirreled away
somewhere as part of the "permanent database" and hidden behind the
network management code (NML). You talk to network management with the
NICE protocol. NICE looks crazy at first but it starts to make sense when
you stare at it for a while. Just keep in mind that there's no such thing
as a definitive authority for the name of a node; you may get different
names for the same address, depending on which node you ask. It happens
in practice. :-(
I think it would take a very long time to get much information about node
names by sniffing NICE passively, unless your site does a *lot* of remote
management. It might be best to use either a hand-built table or a
manually configured "authoritative" host, and just live with any
occasional omissions or discrepancies. Long ago and far away I wrote a
gadget to walk the network and suck out all nodes' name tables, but the
fundamental incoherence of the data never admitted of any satisfactory way
to create a single view of it all.
--
Mark H. Wood, Lead System Programmer mwood@xxxxxxxxx
"Where's the kaboom? There was supposed to be an Earth-shattering kaboom!"
-- Marvin Martian, 01/01/2000 00:00:00
