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
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