10. Conclusions and Recommendations

In 1992, when CIDR was first developed, there were serious problems

facing the continued growth of the Internet. Growth in routing state

complexity and the rapid increase in consumption of address space

made it appear that one or both problems would preclude continued

growth of the Internet within a few short years.

Deployment of CIDR, in combination with BGP4's support for carrying

classless prefix routes, alleviated the short-term crisis. It was

only through a concerted effort by both the equipment manufacturers

and the provider community that this was achieved. The threat (and,

perhaps in some cases, actual implementation of) charging networks

for advertising prefixes may have offered an additional incentive to

share the address space, and thus the associated costs of advertising

routes to service providers.

The IPv4 routing system architecture carries topology information

based on aggregate address advertisements and a collection of more-

specific advertisements that are associated with traffic engineering,

multi-homing, and local configuration. As of March 2005, the base

aggregate address load in the routing system has some 75,000 entries.

Approximately 85,000 additional entries are more specific entries of

this base "root" collection. There is reason to believe that many of

these additional entries exist to solve problems of regional or even

local scope and should not need to be globally propagated.

An obvious question to ask is whether CIDR can continue to be a

viable approach to keeping global routing state growth and address

space depletion at sustainable rates. Recent measurements indicate

that exponential growth has resumed, but further analysis suggests

that this trend can be mitigated by a more active effort to educate

service providers as to efficient aggregation strategies and proper

equipment configuration. Looking farther forward, there is a clear

need for better multi-homing technology that does not require global

routing state for each site and for methods of performing traffic

load balancing that do not require adding even more state. Without

such developments and in the absence of major architectural change,

aggregation is the only tool available for making routing scale in

the global Internet.