BGP Route Reflector - RR vs Confederation is one of the first things Network Engineers would like to understand when they learn both of these Internal BGP scalability mechanisms. For those who don't know the basics of these mechanisms, please read BGP Route Reflector in Plain English and BGP Confederation Blog posts from the website first.
So, we consider BGP RR compare to Confederation to be more scalable because inside Sub-AS still full-mesh IBGP might be used. If RR inside Sub-AS is deployed, then configuration complexity would increase.
Luster list is, when the route passes through the routers, revert router adds its Cluster-ID into the Cluster list, if same Cluster-ID update comes, BGP update is not accepted, thus routing loop is prevented.
But in practice, as said above, single BGP AS and single IGP routing protocol designs are much more common in real-life networks. But the BGP confederation is almost always the opposite. BGP Confederation is seen in real life because of Mergers and Acquisitions. The companies before the merger and acquisition might be using different IGP protocols and usually, they continue to use different IGP protocols.
The reason they continue to use different IGP protocols is, that their network engineers get familiar with the protocol over years, operatinally and design-wise, thus it doesn't make sense to have a common IGP and push the engineers to learn whichever that IGP. Although in the above list and in general there might be many more comparison points between BGP RR vs Confederation, for this post hopefully it is enough and was useful for our readers.
Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021
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