From: diptish doshi (diptishdoshi007@yahoo.com)
Date: Mon Feb 21 2005 - 01:19:10 GMT-3
hi there ,
I really doubt about the actual routing taking
place ... i mean in the routing table ... 2 paths will
be shown for the same destination ( 10.0.0.0/24 ) but
how do u think it would be possible to reach both the
CE ( CE advertising 10.0.0.0 ) from any PE in the
network at a same time ?? IT WOULD BE ONLY POSSIBLE
IF BOTH ARE IN DIFFERENT MPLS-VPN .
Please also do let me know if any other possiblities
.
Thanx and regards,
Diptish .
--- Paresh Khatri <Paresh.Khatri@aapt.com.au> wrote:
> Hi Andre,
>
> Let's call the PE setting the LP to 100 - PE1
> Let's call the PE setting the LP to 150 - PE2
> The third PE is, of course, PE3.
>
> I assume there is a full MP-BGP mesh between the 3
> PEs.
>
> When PE1 receives the BGP route from PE2, it will
> select that route as the best path. Therefore, if
> it has previously advertised the route that it
> learnt from the CE (with a LP of 100), it will
> withdraw that route. Since this is IBGP, it will
> not be advertising any route for that network at all
> now, to the other PEs. This behaviour stems from
> the fact that a BGP peer only advertises what it
> considers to be the "best" path. For PE1, the best
> route is through PE2, so it does not advertise it's
> locally learnt route. The only PE on which you
> should see both routes is PE1.
>
> HTH,
> Paresh.
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com]On Behalf Of
> Andre Scalco
> Sent: Saturday, 19 February 2005 02:00 PM
> To: ccielab@groupstudy.com
> Subject: MPLS MP-BGP router behavior
>
>
> I'm testing some features of MPLS in a LAB and I got
> a scenario that I would like to discuss with you.
>
> I have two CEs configured injecting the same network
> (10.0.0.0/24) to their respective PEs, one PE is
> setting the Local Preference as 100 and the other
> one as 150.
>
> On a Third PE I do see the network 10.0.0.0/24 being
> correctly learned from the PE that is setting the LP
> as 150, but I don't actually see on my bgp table for
> that VRF the other possible path from the PE that's
> setting as 100.
>
> My assumption is that when the Third PE do the
> "scan" to place that 10.0.0.0/24 under the VRF it
> does select only one possible path regardless the
> network is coming from more than one place. However
> if I do a "Show ip bgp vpn rd all" then I should see
> this network from the two PEs that are advertising
> this network.
>
> So in other words, in MP-BGP I should consider this
> rules with extended community RT before any standard
> best path selection algorithm "weight,lp,med,etc"
>
> Let me know what you guys think,
>
> Andre
>
>
> Best Regards,
>
> Andre Scalco
> "Think Outside the Bun"
>
> ---------------------------------
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>
>
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