Internet routing is based on the idea that optimal paths can be dynamically calculated because routers carry information about all network paths in memory. With the massive number of possible paths and new networks being introduced daily, it’s impractical to do this, so most routers fall back on a set of default routes to handle most of their traffic. While a system to optimize routing is theoretically possible, the very flat organization of networks and domains means that it’s not practically possible with IPv4. The exception here is the set of backbone Internet servers that must carry the load and determine all network paths that cannot be computed by individual nodes, placing an onerous burden on some service providers.

IPv6 aims to change this situation by implementing a hierarchical model for addressing, providing an explicit set of domains in the address to ensure that destinations can be resolved at a more local level. Thus, a router does not need to have knowledge of a large set of possible network destinations—the appropriate destination router can be determined from the address. The provider field in the address takes on the role of providing a first-glance indication of a packet’s ultimate destination. At the same time, changes in the structure of the Internet cannot be reliably predicted, so any routing system must be flexible enough to support structural changes down the line.

A number of different routing algorithms are supported by IPv6, including a number that are compatible with IPv4:

  • Open Shortest Path First (OSPF)

  • Routing Information Protocol (RIP)

  • Inter-Domain Routing Protocol (IDRP)

  • Intermediate System to Intermediate System Protocol (ISIS)

Routing extensions are also available through a header in the IPv6 extended header segment. These extensions include the ability to specify intermediate hosts or specific packet paths, which can then be reversed to ensure that a reply packet is delivered back to the sender using the same path. This approach has great benefits to users of mobile telecommunications technologies such as mobile phones, because the highly dynamic path back to its source does not need to be recomputed by intermediate routers.

Part I: Solaris 9 Operating Environment, Exam I