Studying for the CCNP Route 300-101 Route exam, there is no discussion of Border Gateway Protocol(BGP) Route Reflectors. It doesn’t even make the exam blueprint. BGP Route Reflectors are one of the most important elements for multi-home, multi-location BGP. This blog post is not going to be a lesson in BGP, as there are plenty of resources do a great job explaining the topic. Within an Autonomous system(AS) if there are multiple BGP routers, an iBGP full mesh is required. Its a fancy way of saying all the BGP routers need to be connected within an AS. Let’s take an example of a large company which has Internet peering in New York, Atlanta and San Francisco. If the large company is the same AS number, that means it has at least 3 BGP routers, and for business reasons, the routers are dual and dual homed. That makes 6 BGP routers. Remember the formula for a full mesh is: N(N-1)/2. Based on the formula, it would require 15 iBGP peering connections. iBGP makes a logical connection over TCP, but it still needs 15 configurations. This is a small example, but it doesn’t scale if we increased to 10 routers, that means 45 iBGP connections and configurations.
What does a route reflector do?
A Route Reflector readvertise routes learn from internal peers to other internal peers. Only the route reflector needs a full mesh with its internal routers. The elegance of this solution is that it is a way of making iBGP hierarchical.
The previous example of 6 routers, there are many ways to organize the network with Router Reflectors. One Cluster with two route reflectors, two clusters with two route reflectors, etc.
The astonishing part is something so fundamental to leveraging BGP is not cover on the CCNP Routing Exam according to the exam blueprint.
Studying for the CCNP Route 300-101 Route exam, there is no discussion of Border Gateway Protocol(BGP) Route Reflectors. It doesn’t even make the exam blueprint. BGP Route Reflectors are one of the most important elements for multi-home, multi-location BGP. This blog post is not going to be a lesson in BGP, as there are plenty of resources do a great job explaining the topic. Within an Autonomous system(AS) if there are multiple BGP routers, an iBGP full mesh is required. Its a fancy way of saying all the BGP routers need to be connected within an AS. Let’s take an example of a large company which has Internet peering in New York, Atlanta and San Francisco. If the large company is the same AS number, that means it has at least 3 BGP routers, and for business reasons, the routers are dual and dual homed. That makes 6 BGP routers. Remember the formula for a full mesh is: N(N-1)/2. Based on the formula, it would require 15 iBGP peering connections. iBGP makes a logical connection over TCP, but it still needs 15 configurations. This is a small example, but it doesn’t scale if we increased to 10 routers, that means 45 iBGP connections and configurations.
What does a route reflector do?
A Route Reflector readvertise routes learn from internal peers to other internal peers. Only the route reflector needs a full mesh with its internal routers. The elegance of this solution is that it is a way of making iBGP hierarchical.
The previous example of 6 routers, there are many ways to organize the network with Router Reflectors. One Cluster with two route reflectors, two clusters with two route reflectors, etc.
The astonishing part is something so fundamental to leveraging BGP is not cover on the CCNP Routing Exam according to the exam blueprint.
