Re: bgp best path confusion

Indeed, Thanks a lot.

how could I skip it ? I always looked at med, never the IGP metric.

On Thu, Aug 30, 2012 at 1:48 AM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> 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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>>>
>>
>>
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>>
>>
>>
>>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina

Blogs and organic groups at http://www.ccie.net
Received on Thu Aug 30 2012 - 02:10:20 ART