Can anyone help clarify what should happen in this
scenario please with and without 1583 compatibility.

Which path is correct to this external destination
which is advertised as a type 1 external from ASBR
RTR1. Specifically I am considering the non-backbone
intra-area vs backbone intra-area rule.

My question relates to which next hop RTR4 should
install and advertise a metric for.

This is the scenario.

  48.0.1.0/24 (External Route)
      |
      |
   RTR1------Area 0 ---RTR2---Area1
      | \ ---- |
      | \ |
  Area 2 Area0 RTR5
      | \- |
      | \ |
   RTR 3--Area2----Rtr4---Area1-|

From the perspective of RTR5
the cost to 48.0.1.0 is 9 via RTR4-RTR1
                        10 via RTR2-RTR1
                        13 via RTR4-RTR3-RTR1

Is it correct for RTR4 to advertise a metric based on
a path via RTR3 because this subscribes to the
non-backbone intra-area rule from its perspective or
should it advertise the backbone path/metric via RTR1
?

I am not clear as to whether it is possible to route
from non-backbone to non backbone.

Because RTR4 is an ABR in area 1 & Area 2 is it
correct for RTR4 to subscribe to the intra-area
non-backbone rule and advertising the route/cost via
RTR3 through area 2 ? i.e. should RTR4 advertise the
cost to RTR5 based on going through the non-backbone
area 2, and not its backbone area connection even
though it is receiving on a non-backbone interface ?

I am not clear as to whether it is legal to route
through multiple non-backbone areas if you receive a
packet from a non-backbone area.

Thanks

Paul

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