This is the final article in the MPLS Intro Series and will quickly mention the need for route reflectors. This need is driven by the iBGP requirement for a full mesh of peers. This means that a network with only 4 PE nodes would have 6 iBGP peering sessions. This is calculated as n(n-1)/2 where n is the number of PE nodes required for a given topology.
As the scale grows, the need for a centralized peering point becomes obvious. For example, a network with 10 PE nodes would have 45 iBGP sessions to meet the full mesh requirement. Route reflectors overcome this rule by becoming a central point that can advertise routes between iBGP “route reflector clients”. The diagram below actually has more peering sessions than the one above (without RR). However, as a network continues to grow, the full mesh becomes quite challenging.
This is the extent of what I really wanted to cover in this introductory level article and this article concludes the MPLS Intro Series. If you want to learn more about VPNv4 and route reflectors, you can check out this video below.
Disclaimer: This article includes the independent thoughts, opinions, commentary or technical detail of Paul Stewart. This
may or may does not reflect the position of past, present or future employers.