09-10-2018 04:53 AM - edited 03-05-2019 10:54 AM
I referred BGP path selection algorithm from below link
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html
Can someone help to understand why Step #10 is only for external peers? Why is this rule not applicable for iBGP peers?
10.
When both paths are external, prefer the path that was received first (the oldest one).
This step minimizes route-flap because a newer path does not displace an older one, even if the newer path would
09-10-2018 06:08 AM
Why is this rule not applicable for iBGP peers?
When a BGP speaker receives an UPDATE message from an internal peer, the receiving BGP speaker SHALL NOT re-distribute the routing information contained in that UPDATE message to other internal peers
(unless the speaker acts as a BGP Route Reflector [RFC2796]).
Please also read this post -
http://www.practicalnetworking.net/stand-alone/bgp-oldest-path/
09-10-2018 08:23 AM - edited 09-10-2018 11:01 AM
@omz , Thanks but still the question remains unanswered..
I will explain with scenario.
Consider attached topology. Here R3 receives route 10.10.10.1/24 from R2 and R1.
Considering all criteria same, we reach step #10 of path selection criteria.
In this case, prefer oldest entry is not applicable at R3
So why is that, prefer oldest entry applicable to paths received from eBGP peers only?
09-10-2018 10:37 AM
Does R1 receive route 10.10.10.1/24 from R2 and R3 only? Not from R4 also?
What does oldest entry is not applicable at R3 mean? R3 becomes unreachable?
R1 is receiving the route from R2 via iBGP or through R3?
09-10-2018 11:07 AM
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