3 Mar
2020
3 Mar
'20
7:13 p.m.
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?