Re: OSPF Area0 Vs Non-Zero Area [ Anyone Please ]

Thank you Rob for the reply- Sorry if I have created a confusion, but
topology as below:

R6 (A1) - Virtual Link - R1 (A0) (In a way R6 is also connected to A0, via
Virtual Link.
(A1)
  | R6 is connected to R4 in area 1
(A1)
 R4

The route is preferred over area 1 because it is shortest. This is default
behaviour of Cisco OSPF implementation.

So what I understand from your email is that it will never prefer route via
non-zero area, meaning the specified route is always routed via area 0. Is
this what you mean? but as per my understanding by default it can select
route via non-zero area if that is the shortest and it does NOT have to
choose route, routed via area 0 - If you want to change this behaviour and
force to use route via area 0, then we need to disable capability transit.

 Thanks again -

Regards,

Bilal Hansrod

On Sun, Nov 7, 2010 at 8:05 PM, Rob Clav <robclav_at_gmail.com> wrote:

> Hi Bilal,
>
> the questions is, Why all the areas must be connected to Area 0, and what
> happens if you lose the connectivity to area 0?
> Basically, I recommend to you think about, how do you think ospf avoid
> routing loops when dijkstra's algoritm is calculating the shortest path?
> How other dynamics routing protocols as RIP or BGP do it? Maybe
> Split-Horitzon?
>
> So the answer to your q|estions:
> OSFP, don't use the shortest path from "R6" to "R1" thru area 1 because
> doing that you can loop the network. The mechanism that OSPF has is use
area
> 0 as a central point. So you are nearest of farest from area 0 non nearest
> or farest from device A to B.
> If you add the cost from router 6 to area 0 and later you add the cost from
> router 1 to area 0, and inside the area 0 to the DR if you have it, then
you
> will have "total cost".
>
> You need to add your own cost, because the cost is calculate it, from
> router 6 to the DR(itself) PLUS the other router R1 to the DR. At this last
> point is when you are adding your own cost, because the total cost is from
> area 0 and to area 0. Non from router 6 to router 1.
>
> HTH,
> Robclav
>
> --
> Robert Clavero
> CCIE RS/wr, CCNP, CCSP, CCSE NGX, SCSA 9, WLFES, BNP y JNCIA WX
> blog:http://robclavbcn.blogspot.com
>
> web:http://www.kubsolutions.com

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Received on Sun Nov 07 2010 - 21:37:26 ART