From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Wed May 12 2004 - 08:38:09 GMT-3
Howard C. Berkowitz wrote:
> At 6:07 PM +0300 5/11/04, Dan wrote:
>
>> Hello all,
>>
>> I searched the archive and found no answer:
>>
>> How does OSPF selected routes from its database?
>> Does it prefers LSA X over LSA Y? or is the cost is have ultimate
>> preference?
>> Are LSA 5/7 considered as inter-area or intra-area?
>
>
> They are considered external.
>
>>
>> Could you point me to the relevant url?
>>
>
>
>
>
> (URL eater food)
>
>
>
>
>
>
> The OSPF working group official page is
> http://www.ietf.org/html.charters/ospf-charter.html
>
> This will give you the current standard:
> http://www.ietf.org/rfc/rfc2328.txt Other documents will give you some
> special cases.
>
> The basic rule:
> Always prefer intra-area over inter-area over external 1 over
> external 2.
> Within a category, take the longest match.
> To break ties with equal match length, use route cost.
> If there are still ties, load-share up to the configured limit of
> parallel routes.
what is longest match here ?
AFAIK, OSPF redistributes all known prefixes, and does that even for
prefixes that overlap. OSPF can only compare routes that are strictly
the same, i.e. network and mask.
longest match criterium will be applied by the IP forwading engine, and
that will eventually take precedence over all other things.
>
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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