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Michal Rzepecki
Beginner

BGP RR - one or two paths

I have two route reflectors (not clustered) in my lab and 10 PE routers. All PE routers have two iBGP sessions established - one to RR1 and one to RR2.
Should I see one or two paths in BGP VPNV4 table for for a prefix advertised by a PE router?
For some prefixes I can see two paths - with the same prefix and next hop - one reflected by RR1 and another reflected by RR2. Only one path is the best of course.
For some other prefixes I can see one path reflected by RR1.
I'm not sure but I think that two paths reflected by two RRs are expected in case of route reflectors that are not clustered. Can anyone cofirm?

Strangest thing is that it depends which PE router I'm checking on.
If I'm checking on one of IOS XR PE routers I can see two paths (from RR1 and RR2) for every prefix advertised by other IOS XR PE routers and only one path for every prefix advertised by IOS XE PE routers.
Opposite situation is when I'm checking on one of IOS XE PE routers - I can see two paths (from RR1 and RR2) for every prefix advertised by other IOS XE PE routers and only one path for every prefix advertised by IOS XR PE routers.
Has anybody seen something like that before?

5 REPLIES 5
balaji.bandi
VIP Expert

You can configure backup path - below thread help you (is this what you looking or i miss read the requirement)

 

https://community.cisco.com/t5/xr-os-and-platforms/xr-as-rr-with-bgp-additional-paths/m-p/3019224

 



BB


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Thank you for reply but this is not related to my questions.

MHM Cisco World
Collaborator

Screen Shot 2021-05-01 at 4.55.17 AM.pngScreen Shot 2021-05-01 at 4.55.24 AM.png

Thank you for reply. your answer is not related to my questions.

I attach Photo to what RR do when receive two same Prefix, 
RR will send the best path to client BUT, RR behavior different in XE and XR.  

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