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.
BGP Route Reflector vs BGP Confederation
There are many differences when we compare Confederation vs Route Reflector and in this post, some of the items in the comparison chart will be explained.
BGP Route Reflector vs Confederation Scalability
Both of these techniques are used in Internal BGP for scalability purposes. But BGP RR changes the Full Mesh IBGP topologies to the Hub and Spoke. BGP confederation divides the Autonomous System into the sub-ASes but inside every Sub-AS, IBGP rules are applied. Inside BGP Sub Autonomous System, full Mesh IBGP or Route Reflector is used.
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.
BGP Route Reflector vs Confederation Loop Prevention
BGP Route Reflector in order to prevent the routing loop uses two BGP attributes. Originator-ID and Cluster List. Originator ID is basically if BGP RR sees its own Router ID in the BGP update, it will not accept the update so routing won't form.
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.
Using Different IGP in BGP Route Reflector and Confederation
BGP RR is used in a single BGP AS. Inside single BGP AS, usually single IGP is used. But this is not the hard rule. In theory, there can be multiple IGP protocols in different parts of the network for internal prefixes and customer prefixes, or Internet prefixes still can be carried within BGP.
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.