[HECnet] Johnny: Can you add some new nodes

[Paul_Koning at Dell.com]

On Aug 10, 2012, at 5:52 AM, Johnny Billquist wrote:

...
It might be worth understanding that there is nothing technical added by going to multiple areas. It is just a complication which allows you to have more nodes, but at the cost of more complex routing.

Even within one area, you can have a large number of hops between nodes. Makes no difference to DECnet. The rules for the topological layout is simple:
1. End-nodes needs to be adjacent to atleast one level 1 router.
2. All level 1 routers in an area must be able to talk with all other level 1 routers. And only level 1 routers route messages within an area, which means you cannot have an endnode in the chain.

Essentially right.   But area routers include L1 router functionality (there is no such thing as an L2-only router).   So for "L1 router" you should instead say "L1 or area router".

Also, endnodes and L1 routers can only talk to a router that's in the same area as they are.

Also, each area must not be partitioned, and the L2 net must not be partitioned.   The L2 net is defined by the L2 routers and their direct connections, so a pair of L2 routers connected by an L1 router are not connected at L2.

Finally, an oddball case: if a LAN does not have any routers on it, then the endnodes on it can communicate among each other, even if they are in different areas.   But as soon as there are routers on the LAN, the rules you mentioned apply.   So suppose you have a two-area LAN, and you want to route away from it.   The minimum change you need is to add one L2 router in the one area, and another L2 router in the other area.

	paul