From: Carlos Campos Torres \(ccampost\) (ccampost@cisco.com)
Date: Tue May 23 2006 - 17:18:19 ART
As Tony said, if you do a virtual-link over Area 1, since the
virtual-link will be an extension of Area 0, you are making R2 believe
that both routes are being received on the same Area and will be treated
as intra-area, just as correctly said before by Tony, make sure you have
the same costs
Regards,
Carlos Campos
(919) 392-6285
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Howard C. Berkowitz
Sent: Thursday, May 18, 2006 6:01 AM
To: ccielab@groupstudy.com
Subject: Re: More on OSPF route selection
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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