[HECnet] Effects of Rogue Duplicate HECnet Node?

[Thomas DeBellis]

You may be talking about a number of things here.  DECnet node numbers 
are something (very) vaguely like IP tuples, except with half the bits 
and fixed fields.  The upper 6 bits constitute the area, the lower 10 
bits constitute the number within area.  This is what I recall:

 1. If the node number's name is not defined to other systems, then many
    user level programs will not be able to see if. Tops-20 won't able
    to build a connection.
      * Phase II DECnet used node names directly, I think.
 2. If the number is the same as another system in different area, then
    everything is fine except for 1.
 3. If the number is the same as another system in the _same_ area, then
    somebody will become 'unhappy'.
      * I don't remember how the adjacency is reported for point-to-point.
 4. If you think of MAC address clash on the same Ethernet segment as
    opposed to different segments, you may appreciate a similarity.
 5. I don't remember the finer details of the differences between a
    level 1 and 2 router.
      * A level 1 router handles routing through point-to-point in the
        same area.
      * If a different area is requested, then the level 1 router hands
        the packet to a level 2 router.

First, if the node number

On 3/3/20 12:54 PM, Mark J. Blair wrote:
> I had a shower thought that I'd like to run down in order to better understand how DECnet routing works. Ok, I wasn't actually in the shower.
>
> Let's say that my local DECnet is successfully hooked in to HECnet. For the sake of discussion, imagine I'm using PyDECnet to connect to my upstream node, and I don't have my own area number. That means that my PyDECnet node would be a level 1 router, right?
>
> Now, imagine that I inadvertently bring up a system on my local ethernet with an uncoordinated DECnet node ID. Perhaps I booted some random RL02 pack in my VAX without remembering to unplug the ethernet cable, or booted a random disk image in SIMH with it connected to the TAP device. Just to make things exciting, let's say that the system comes up with a node ID that properly exists elsewhere in HECnet.
>
> If the node ID happens to be in the same area that I'm properly in, does the adjacency detection find it and break things? What if it comes up with a node ID in a different area? Just how much trouble would this cause?
>
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