Chapter 10. Extensibility

The 1980s and 1990s were the decades of entrepreneurship for the Internet. The World Wide Web changed the Internet from a small community of academics and technophiles into a huge worldwide marketplace. The carriers and ISPs focused on bandwidth, performance, and reliability. By the turn of the century, however, these infrastructure companies began changing their focus. Most offered similar levels of service, so the only way for them to compete with each other was through lower prices. Carriers and ISPs began looking for new service offerings to make up for the lost revenue of increasingly commoditized IP packet transport. Typical of the new services being offered wereand arevoice and video over IP, conference services, and virtual private networks (VPNs).

But underlying all these new services was still plain old best-effort IP. In fact, most service providers began moving services traditionally offered over Frame Relay and ATM to their IP infrastructures to reduce capital and operational expenses. A set of intermediate technologies are required to make the IP infrastructure appear better than best efforta set of "building blocks" that enable new commercial service offerings. These intermediate technologies include Multiprotocol Label Switching (MPLS), multicast IP, and, increasingly, a new version of IP, IPv6.

Such intermediate technologies require information about the underlying IP network to run correctly, and the best source of that information is the IGP. Rather than inventing a new IGP, designers have added new capabilities to OSPF and IS-IS in recent years. This chapter explores the general concept of extending the protocols to support new capabilities. Chapters 11-13 look at specific extensions to OSPF and IS-IS.