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From: SXJLH@ALASKA.BITNET.UUCP
Newsgroups: comp.os.vms
Subject: decnet-span
Message-ID: <8704150410.AA23902@ucbvax.Berkeley.EDU>
Date: Tue, 14-Apr-87 11:33:00 EST
Article-I.D.: ucbvax.8704150410.AA23902
Posted: Tue Apr 14 11:33:00 1987
Date-Received: Sat, 18-Apr-87 00:45:21 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
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For those interested in how to have a decnet link to an outside decnet network
without losing complete control of your own decnet network (i.e. how do
i hook up with SPAN and not have to let them assign all my nodes) here is
how the University of Alaska managed it (somewhat).

First, you use an undocumented/unsupported decnet feature.

Second, you have to compromise some in accepting the area number
and address assigned by span only for your node.


The adjacent node (i.e. span node) must be an area router (EXECUTOR TYPE AREA)
and must set the circuit to your node as a TRANSPORT TYPE NONROUTING IV.
You must also have your node set as an area router and set your circuit to the
adjacnet node as a transport type nonrouting iv.  What this configuration
appears to do is to not have the area routers route area info. In more simple
terms you only know about the adjacent node (appears as an end node) and
the other network (i.e. span) only sees your node as an end node.  They
can not see any other nodes that are attached to your node.

This may be more difficult for some folks than it was for us because our
problem was that we had an adjacent node that wanted to be able to access
span and our node at the same time.  So now they can access span and our
node but not any other nodes in our network.  We can not access any node
in span except our adjacent node.  You can use 'poor mans routing' to
access the other nodes (e.g. $ dir adjancent_node::span_node:: ).  And to
be able to login to those nodes you would first have to login to the
adjacent node.

Follows is a diagram of the configuration.


                 +--------- same area -------------+
                 (area and address assigned by span)
                 |                                 |
                 |         transport type          |
  Your network --|  your  ------------------ span  |-- span network
                 |  node   nonrouting iv     node  |
                 |                                 |
                 +---------------------------------+
                     ^                        ^
                     |                        |
                  this node can            this node can
                  access your              access your node
                  network and              and span network
                  span node


Probably for this to work for most others, it would be necessary to have two
nodes in your network given area and address numbers by span.

Oh yes, we are using an aysnc circuit, but it will work with a sync circuit
as well, but won't work with an ethernet circuit.  At least not if you have
more than two nodes on the ethernet.  If someone knows how to select part
of an ethernet circuit (una-0) please tell me.

The gotchas are that this 'feature' may go away with any future decnet release.
(Rumored to go away with v5.0, but a supported solution may be available).

Our adjacent node tells me that it appears to work just fine.


Jeff Harrison
sxjlh@alaska.bitnet