From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Thu May 18 2006 - 07:00:42 ART
Roberto Fernandez wrote:
> Friends,
>
>
>
> Thanks for your previous answers, can we establish the following?
>
>
>
> 1 - OSPF always prefers intra-area over inter-area.
>
Correct. This is part of the fundamental design of the protocol and
meant to prevent loops.
> This means that given an existing intra-area route, for a given
> destination; there is no way to trick OSPF into including on the routing
> table an inter-area route (for the same destination), regardless the
> metric values.
>
>
>
> 2 - The only way to trick OSPF into including new routes on the routing
> table for a given destination is working on metrics, (through interface
> cost, neighbor cost or auto cost)
>
>
>
All of these are subject to the rule intra-area is preferable to
inter-area, which is preferable to external 1, which is preferable to
external 2. While the types of internals are a refinement, these are
generally architectural elements of the OSPF design and prevent loops.
> Now a remaining question:
>
>
>
> If there are two inter-area routes on a given ABR (R2), one coming
> through area0 (through R1) and the other coming from area1(through R2),
> It is there any known trick to make OSPF include the area1 route
> together with the area0 route?
>
I'm not sure if I understand the drawing sufficiently, but if they are
both inter-area routes and the interface metrics add up to the same
route cost, then they will be equal-cost and should appear as load-balanced.
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