[c-nsp] Different Areas OSPF Paths

[Asbjorn Hojmark - Lists]

> Route-Site-A-2 is the lowest cost to reach Site-B , On Core 
> router at Site-A you'll see Router-Site-A-2 and Site-B as a
> selected path....but when you go to any ABR... you'll see its
> own Tunnel as the best exit path via OSPF, although other ABR's
> are recieving shortest path via OSPF neighbours.

The shortest path algorithm really says 'shortest path via one
area, then shortest path via area 0, and finally shortest path
via other area'.

Since each ABR has a connection to both area 0, 3 and 4, they'll
send traffic from 3 to 4 via their own direct connection to 4.
They will *not* send the traffic via area 0 as that would not be
the shortest path.

> Another question is: Area-3 doesn't wantes to recieve routes 
> from Area-4 and vice versa but connection to Area 0, is
> distributing the routes/flooding to both these areas.
> 
> I have tried making both Area 3 & 4 a stub but it's not 
> helping...

You have to make the areas totally stubby if you don't want any
routes flooded from area to area. Then Router-Site-C and Router-
Site-B will only see their own respective area's routes and a
default.

-A