[j-nsp] About RD in vpls multi-homing environment.

[Adam Vitkovsky]

Hi Nat,

You should always want to use unique RDs (possibly type-2 RD using router-id IP address) in any MPLS services when RRs are involved.
RD as the name suggests makes the route (or any information carried) distinguishable/unique thus not subject for BGP best path selection. 
As you know BGP only advertises best-paths to its neighbours so if two sites advertise the same information to the RR -RR will select only one and advertise it to the rest of the AS -unless you make the otherwise same information unique by prepending it with a unique RD. 
AS you might rightly infer using unique RDs will increase the amount of information flooded to the PEs but the advantage, as Sebastian pointed out, is that PEs will have a backup route at hand and thus can use techniques to fast failover to the backup path if the primary path is down.
 

adam
> -----Original Message-----
> From: juniper-nsp [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf
> Of Pyxis LX
> Sent: 11 April 2015 19:18
> To: juniper-nsp at puck.nether.net
> Subject: [j-nsp] About RD in vpls multi-homing environment.
> 
> Hi, All.
> 
> I am not sure whether PEs connected to the same vpls site should be
> configured with the same RD or not.
> 
> "JNCIS-SP Study Guide Part 3" P.415 states that both PE connected to
> the same site should be configured with the same RD.
> (The topology chart is available at P.409, PE2 & PE3 connect to the same site)
> 
> However, when I configure them with the same RD, PE3 will not announce
> any l2vpn routes to other PEs, is that normal?
> 
> And I found another configuration example on Juniper website:
> 
> http://www.juniper.net/documentation/en_US/junos14.2/topics/topic-
> map/vpls-bgp-multihoming.html
> 
> This example suggests that PE1 and PE2 should use different RDs.
> 
>  Which one is correct, or I take the wrong example?
> 
>  Thank You.
> 
> -Nat
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