Choosing routes from Multiple Route Reflectors

[oscardenizjensen]

Hej
Unfortunately I can not test this right now, so I would like some help from community

If I establish IBGP connection on a device to 3 different RRs, and if they all send the same route, will I always install routes from only 1 of the RRs into my RIB? Or will the routes do a "round-robin" style and get installed.

Is there a RR selection process like router-id when receiving same routes?

So if IBGP session to "main" RR goes down (and assuming I don't use Add-path or PIC-EDGE), then will my device need to re-populate the RIB with all the routes again from another RR or only part of the RIB?

Regards

[David Ruess]

@MHM Cisco World and @oscardenizjensen  after checking again I got the same result as my answer above. I have listed the output and attached the config for all 4 routers. I also used the CSR routers in my CML lab as they have a specific command for BGP best path selection that tells you why it was selected as the best (pretty neat feature) and it shows the highest Neighbor address as the reason as why the path was not chosen.

R4#sh ip bgp
BGP table version is 3, local router ID is 4.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
x best-external, a additional-path, c RIB-compressed, 
t secondary path, L long-lived-stale,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*>i 10.10.10.10/32 1.1.1.1 0 100 0 i
* i 1.1.1.1 0 100 0 i
R4#
R4#sh ip bgp 10.10.10.10
BGP routing table entry for 10.10.10.10/32, version 3
Paths: (2 available, best #1, table default)
Not advertised to any peer
Refresh Epoch 1
Local
1.1.1.1 (metric 131072) from 2.2.2.2 (22.22.22.22)
Origin IGP, metric 0, localpref 100, valid, internal, best
Originator: 1.1.1.1, Cluster list: 22.22.22.22
rx pathid: 0, tx pathid: 0x0
Updated on Nov 10 2023 18:13:45 UTC
Refresh Epoch 1
Local
1.1.1.1 (metric 131072) from 3.3.3.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, valid, internal
Originator: 1.1.1.1, Cluster list: 3.3.3.3
rx pathid: 0, tx pathid: 0
Updated on Nov 10 2023 18:13:33 UTC
R4#

R4#sh ip bgp 10.10.10.10 best-path-reason 
BGP routing table entry for 10.10.10.10/32, version 3
Paths: (2 available, best #1, table default)
Not advertised to any peer
Refresh Epoch 1
Local
1.1.1.1 (metric 131072) from 2.2.2.2 (22.22.22.22)
Origin IGP, metric 0, localpref 100, valid, internal, best
Originator: 1.1.1.1, Cluster list: 22.22.22.22
rx pathid: 0, tx pathid: 0x0
Updated on Nov 10 2023 18:13:45 UTC
Best Path Evaluation: Overall best path
Refresh Epoch 1
Local
1.1.1.1 (metric 131072) from 3.3.3.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, valid, internal
Originator: 1.1.1.1, Cluster list: 3.3.3.3
rx pathid: 0, tx pathid: 0
Updated on Nov 10 2023 18:13:33 UTC
Best Path Evaluation: Higher peer address
R4#

This is the peer address from the neighbor command and not the RID. You can tell becasue the RID of R2 is 22.22.22.22 which is higher than R3s of 3.3.3.3. However R3s neighbor address is 3.3.3.3 and R2s neighbor address is 2.2.2.2

[MHM Cisco World]

Thanks a lot 

I will check again abd update you.

Thanks A Lot
MHM

[MHM Cisco World]

I make check Yesterday, 
in my lab I connect RR to eBGP 
in your lab you connect RR to iBGP two clients and the behave we see is the selection of prefix learn from RR which originate from other RR-clients.

Thanks A Lot
MHM