[quagga-users 7094] Re: Attempt to change route

Paul Jakma paul at clubi.ie
Wed Jun 14 21:29:59 IST 2006


On Wed, 14 Jun 2006, Dmitriy Gorbenko wrote:

> Here are network diagram:
>
>                                      +--------+
>                       +--------------|   B    |
>                       |   10.0.0.3/24+---+----+
>                       |                  |10.0.1.1/24
>                       |                  | cost 1
>                       |                  |
> 10.0.1.2/24            |                  |
> +--------+             |            +-----+-----+
> |   A    |-------------+------------|     C     |
> +--------+ 10.0.0.1/24  10.0.0.2/24 +-----------+
>          cost 1                          |192.168.0.1/24
>                                          |cost 1
>                                          |
>                                          |192.168.0.2/24
>                                     +----+-----+ 
>
>                                     |    D     |
>                                     +----------+
> I want A send packet to D though B
>
>> However, if only C connects to 192.168/24, then you can never
>> make A->C be lower cost than A->B->C.
>
> really ?

Nope. Not with regular SPF.

Only interfaces have costs, and SPF only takes output cost into 
account. Though networks have LSAs, they have no cost associated 
(inherited from the router vertex).

So there's just no way really, afaik, to make a path via A->B-C have 
a lower cost than A->C, when B and C are on the same link as each 
other as far as A is concerned.

The simplest solution might be simply to use something like VLANs so 
that A thinks it has seperate links to B and C.

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
The only time a dog gets complimented is when he doesn't do anything.
 		-- C. Schulz


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