From: Kulcsár
Date: Tue Jul 18 2006 - 07:50:48 ART
No, I think everybody misunderstood.
Two paths, same prefix, next hops different, learned by different IGP routing protocols.
I think I should really lab it up now, no answer yet.
Andras
-----Original Message-----
From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
Sent: Tuesday, July 18, 2006 11:59 AM
To: Kulcsar Andras Benjamin
Cc: Godswill Oletu; Cisco certification
Subject: Re: BGP Bestpath selection
I would go for whatever mech the hosting router uses to choose for the best path. In cisco case, that would be comparing AD if metrics are from different sources. But lab is the answer, just lab it up :)
Kulcsar Andras Benjamin @ 17/07/2006 03:56 -0300 dixit:
> Hi,
>
> I think you misunderstood the problem.
>
> Let's suppose the following:
>
> In the BGP table, I have TWO paths with DIFFERENT next hops. The first
> next hop is learned via rip with metric 2, the second next hop is
> learned via OSPF with metric 1000. What happens? Are the metrics
> simply compared?
>
> -----Original Message-----
> From: Godswill Oletu [mailto:oletu@inbox.lv]
> Sent: Saturday, July 15, 2006 4:55 PM
> To: Kulcsar Andras Benjamin; Cisco certification
> Subject: Re: BGP Bestpath selection
>
>
> Andras,
>
> The best path selection algorithm will look into the routing table to
> determine which IGP route to use.
>
> If the router in question received both RIP & OSPF routes for the same
> destination, the RIP routes will not make it to its routing table
> because the router will pick the OSPF route because of its more
> favored AD and that is the route that the BGP selection algorithm will
> consider.
>
> You can only compare metric among the same IGP, comparing metric among
> different IGP is like comparing apples to orange. EG a metric of 20 to
> OSPF is a very very good metric infact it is the default metric when
> you redistribute into OSPF, but to RIP a metric of 20 do not only mean
> that, the route is dead, it means that the route is DEAD LONG LONG
> TIME AGO!
>
> Godswill Oletu
> CCIE #16464
>
>
> ----- Original Message -----
> From: "Kulcsar Andras Benjamin" <Kulcsar.Andras@kfki-lnx.hu>
> To: "Cisco certification" <ccielab@groupstudy.com>
> Sent: Saturday, July 15, 2006 10:31 AM
> Subject: BGP Bestpath selection
>
>
>
>>Hi everybody,
>>
>>Rule number 8 says: Prefer the path with the lowest IGP metric to the
>>BGP next hop.
>>
>>What happens if the IGP metrics are not comparable? I mean the first
>
> path's
>
>>next hop is learned via OSPF, the other's is learned via RIP. Is
>>simply
>
> the
>
>>numerically lowest metric chosen?
>>
>>Regards,
>>Andras
>>
>>______________________________________________________________________
>>_
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>
>
> ______________________________________________________________________
> _
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-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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