[c-nsp] Decnet, LAT, MOP ... anybody?!?

[Johnson, Neil M]

I used to have to manage DECnet on a manufacturing network.

MOP and LAT are layer two protocols and must be bridged (Sorry).

MOP is DECnet's version of bootp and tftp rolled into one. It is used for
booting diskless workstations and X-Terminals.

LAT is used by VMS systems to send and receive data from terminal servers
(to provide remote serial ports for terminals, printers, etc.). 

We used to bridge LAT and MOP between buildings over an FDDI ring, then ATM.
Both were backed up with a T1. We routed DECnet.

As for weird looking MAC addresses, DECnet Phase IV munges the MAC address
on each router's interface routing DECnet.

When we consolidated buildings I just put all the DEC devices on the same
Vlan. We had to do the same with our HP SRM workstations.

I learned the hard way that DEC servers and workstations don't respond well
to their network links going down. This is especially true of older VAX and
early Alpha architecture machines. The systems would just crash. I ended up
putting all the servers on one switch (a 3524) so that I could do
maintenance on the core switches (6509's) without having to have a VMS guru
on-hand to get the systems back up. 

At home I have an old copy of my course book from a Cisco Introduction to
Routing class I took back in the mid 90's. This was during the time OSI was
supposed to replace TCP/IP. It covered a lot of routing protocols: TCP/IP,
IPX, Appletalk, DECnet, OSI, and many others (even XNS :-) ). Unfortunately
we just moved, so it is buried in a box somewhere.

-Neil

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Netfortius
Sent: Thursday, April 06, 2006 2:32 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Decnet, LAT, MOP ... anybody?!?

On Thursday 06 April 2006 14:03, Brian McMahon wrote:
> On Apr 6, 2006, at 11:48, Netfortius wrote:
> > I am having a little problem with a setup, in regards to some VAX
> > machines on
> > two different LANs. Here is the data:
> > - client needs the functions on the VAX machines, but nobody
> > remembers who put
> > them in;
>
> [...]
>
> > - sniffing at one end I have seen some LAT and MOP traffic, but
> > none of that
> > would appear to leave the confinement of a LAN (except for broadcasts)
>
> LAT for sure, and I think MOP as well, are layer 2 protocols, and
> *must* be bridged.  No layer 3 info, MAC addresses only, nothing to
> route.
>
> LAT .ne. DECnet.  DECnet (there's Phase IV, which is what you
> probably have, and Phase V, which is based on the OSI protocol stack
> (remember when that was going to be the way of the future?)) is
> routable, assuming that you have an IOS feature set that speaks DECnet.
>
> But if your important access is via LAT anyway (mostly seen for
> communication with terminal servers and printers), then you're stuck
> bridging that no matter what.
>
> *WOW*, it's been a long time since those neurons woke up.
>
> --
> Brian McMahon <brian dot mcmahon at cabrillo dot edu>
> Computer Networking and System Administration Instructor
> Cabrillo College, Aptos, California

Thank you for your reply. This is the challenge - I mentioned LAT and MOP as
I 
know they are not routable, but I cannot tell if the traffic I am seeing is 
in real need for bridging or if I see it because it is bridged (does it make

sense? - this is the only way I could describe my problem). 

For example - I am seeing conversation between an interface of one VAX on
one 
LAN (that weird MAC address which is specific to DEC), and the Ethernet 
interface of the Cisco router - which, if it was to be routing - would have 
been indicative of need to cross the boundaries, but which - being that it
is 
identifying by tethereal as LAT, makes me wonder if it is not in fact just 
some broadcast reaching the router, but with no need to traverse it.

Also - as all the VAXes on either side are supposed to boot locally (MOP 
part), I am wondering if the traffic I see being MOP related is not - in 
fact - visible just because I am bridging, not that it really needs to cross

LANs ...

Thanks again,
Stefan
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