Re: bgp best path confusion

metric ?

oo IPX @ 29/08/2012 16:43 -0300 dixit:
> Thanks Gilles,
>
> I added a R4 to the topology, that connects to R2, R3 and R1 over the
> Frame-relay.
> now, R4 is a RR too, and is ibgp peer to R3.
>
> now no direct ibgp peering between, R3 and R2.,
> and R3 and R2 are route-reflector-client of R1 and R4.
>
>
>
> R1------R4
> | \ / |
> | \ / |
> | \/ |
> | / \ |
> | / \ |
> R2 R3
>
>
> R3#sh ip bgp 2.0.0.0
> BGP routing table entry for 2.0.0.0/8, version 17
> Paths: (2 available, best #1, table Default-IP-Routing-Table)
> Flag: 0x900
> Not advertised to any peer
> Local
> 10.1.22.2 (metric 1) from 10.1.13.1 (5.4.2.1)
> Origin IGP, metric 0, localpref 100, valid, internal, best
> Originator: 2.2.2.2, Cluster list: *5.4.2.1*
> Local
> 10.1.24.2 (metric 2) from 10.1.34.4 (4.4.4.4)
> Origin IGP, metric 0, localpref 100, valid, internal
> Originator: 2.2.2.2, Cluster list:* 4.4.4.4*
>
> I guess this one goes to rule 13.
>
>
>
> On Thu, Aug 30, 2012 at 12:55 AM, Gilles Fabre <fabre.gilles_at_voila.fr>wrote:
>
>> Hi
>>
>> this looks like a great design...isn't Route-Reflector supposed to remove
>> the need for Full-Mesh ??
>>
>> anyway, I think in this case Rule #12 applies :
>>
>> 12. If the originator or router ID is the same for multiple paths, prefer
>> the path with the minimum cluster list length.
>> This is only present in BGP RR environments. It allows clients to peer
>> with RRs or clients in other clusters. In this scenario, the client must be
>> aware of the RR-specific BGP attribute.
>>
>> best regards,
>> Gilles.
>>
>>
>>> Message du 29/08/12 ` 19h01
>>> De : "oo IPX"
>>> A : "Cisco certification"
>>> Copie ` :
>>> Objet : bgp best path confusion
>>>
>>> i have a hub and spoke topology, R1 being hub.
>>>
>>> R1-is a Route reflector.
>>>
>>> also, R1, R2 and R3 are fully meshed ibgp peers. with R1, R2 and R3
>>> advertising networks 1.0.0.0/8, 2.0.0.0/8 and 3.0.0.0/8
>>>
>>> *on what level of the bgp path decision making the following route is
>> been
>>> chosen?*
>>>
>>>
>>>
>>> *R3(config-router)#do sh ip bgp 2.0.0.0
>>> BGP routing table entry for 2.0.0.0/8, version 4
>>> Paths: (2 available, best #2, table Default-IP-Routing-Table)
>>> Flag: 0x820
>>> Not advertised to any peer
>>> Local
>>> 10.1.12.2 (metric 1) from 10.1.13.1 (1.1.1.1)
>>> Origin IGP, metric 0, localpref 100, valid, internal
>>> Originator: 2.2.2.2, Cluster list: 1.1.1.1
>>> Local
>>> 10.1.12.2 (metric 1) from 10.1.12.2 (2.2.2.2)
>>> Origin IGP, metric 0, localpref 100, valid, internal, best
>>> *
>>>
>>>
>>> Network Next Hop Metric LocPrf Weight Path
>>> *>i1.0.0.0 10.1.13.1 0 100 0 i
>>> ** i2.0.0.0 10.1.12.2 0 100 0 i
>>> *>i 10.1.12.2 0 100 0 i*
>>> *> 3.0.0.0 0.0.0.0 0 32768 i
>>>
>>>
>>>
>>> Regards
>>>
>>>
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>>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
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