Re: Question about Type2 redistribution in to OSPF

[Acee Lindem <[e-mail]>]

Nikhil Sama wrote:

> R1 will have a cost of 5 to the type-2 external route mentioned.
>
> The reason is, as you mentioned ..
> "Type 2 metrics are assumed to be larger than the cost of any intra-AS
> path."
>
> If there was another type-2 external route available to the same
> destination prefix via another internal ASBR/Next-Hop, then your
> decision on which route to pick should be independent of your cost to
> the different internal next-hop's but based solely on the type 2
> metrics.


This is true as long as the type-2 metrics from the two ASBRs differ.
When they are equal then the OSPF cost to the ASBR/forwarding address is
considered. Refer to section 16.4 in RFC 2328 for the details.


> This would not "necessarily" be the case had you added the internal
> cost(of getting to the next-hop) to the type-2 metric.
>
> Hope this helps !
> /ns
>
> On Wed, 2002-08-21 at 11:21, Mani Devarajan wrote:
>
>>RFC 2328:
>>=========
>>Section - 12.4.4.  AS-external-LSAs
>>
>>Type 2 metrics are assumed to be larger than
>>the cost of any intra-AS path.
>>
>>In one other document I read ,it says that for type 2
>>it will be always external cost irrespective of inter
>>area cost.
>>
>>                          type 2
>>      -----     -----     -----
>>     |     |   |     |   |     |
>>     | R1  |   | R2  |   |ASBR |
>>     |     |   |     |   |     |
>>      -----     -----     -----
>>          |10   |   |10    |  |
>>           -----     ------    ----|
>>                                   | External Network
>>                                   |
>>If ASBR redistributes route for external network at a
>>cost of 5, R1 will have a route to external network
>>with cost == 5 or cost > 10.
>>
>>Thanks in advance,
>><Mani
>>
>>
>


--
Acee