8.5. SCALABILITY DISCUSSION

Scalability is a crucial aspect of any network service. Without scalability, the service becomes the victim of its own success: as the popularity of a service grows, it becomes either technically difficult or economically unsound to provide the service to both new and existing users. When evaluating the scaling properties of BGP/MPLS VPNs one must examine both these aspects and answer the following questions:

  • From a solution point of view, is there a technical upper limit on the maximum number of VPN customers and sites per customer that can be serviced in a given network? In other words, is there a scalability bottleneck in the solution, or can the service be scaled by adding more routers to the network?

  • How does increasing the number of customers impact the cost of the network? In other words, how is the scalability of each of the devices impacted by the growth in the number of customers and routes? At which point must new equipment be purchased?

8.5.1. Potential scaling bottlenecks

The first question is whether there is a scalability bottleneck in the solution. The dimensions in which a VPN service is expected to grow are the number of VPNs, the number of customer sites and the number of customer routes. Growing the VPN service may have implications on:

  1. The provisioning burden on the provider.

  2. The load on routing protocols.

  3. The amount of VPN-related information that must be maintained on the provider's routers.

  4. The amount of bandwidth needed to carry ...

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