Chapter 11. Network Performance Considerations: Coexistence of IPv4 and IPv6

Years of innovation and work to continuously improve various transport technologies and network elements led operators to have high expectations of their networks. Although richness of supported features can differentiate networking equipment, high performance is expected by default. Nothing short of line-rate forwarding of raw traffic is expected for most high-speed interfaces of high-end routers and switches.

During the initial phases of its development, IPv6 was viewed as a mere feature, something new to play with and evaluate. Its implementation in software enabled router vendors to stay on the fast track of integrating the recommendations churned out by the standardization bodies. The IPv6 early adopters, universities and developers were offered the tools to play and experiment with the protocol. Cisco engaged on this path with a phased program that led to Cisco IOS software officially supporting IPv6 features as early as 2001 in release 12.2(2)T.

After the protocol consolidated and matured, the focus moved toward deployment considerations, and that naturally implied focus on IPv6 performance. Fast adoption of features remains important in the case of a still-evolving protocol. However, performance requirements force vendors to look at the entire architecture of their products and work on integrating IPv6 in every aspect of it. To meet competitive performance requirements, depending on router architecture, both software and hardware have to take into account the new protocol.

The whole topic of performance has an additional twist in the case of IPv6. Today, there are a few cases where brand new networks are built specifically for IPv6-based services. For all the other networks, which include the vast majority, the operators ask a natural question: "What is the impact on my network of turning on IPv6?" The IPv4 infrastructure remains the source of revenue and supports the most important services. Bringing IPv6 into the network must not impact it negatively. The performance implications of IPv4 and IPv6 coexistence can push the discussion from the network element level to a system level, a higher level of complexity.

This chapter discusses the various aspects of router performance and the challenges posed by IPv6. It provides information and guidelines on evaluating a router's performance so that you can choose the right router for the job.