9. Analysis of CIDR's Effect on Global Routing State

9. Analysis of CIDR's Effect on Global Routing State

When CIDR was first proposed in the early 1990s, the original authors

made some observations about the growth rate of global routing state

and offered projections on how CIDR deployment would, hopefully,

reduce what appeared to be exponential growth to a more sustainable

rate. Since that deployment, an ongoing effort, called "The CIDR

Report" [CRPT], has attempted to quantify and track that growth rate.

What follows is a brief summary of the CIDR report as of March 2005,

with an attempt to explain the various patterns and changes of growth

rate that have occurred since measurements of the size of global

routing state began in 1988.

When the graph of "Active BGP Table Entries" [CBGP] is examined,

there appear to be several different growth trends with distinct

inflection points reflecting changes in policy and practice. The

trends and events that are believed to have caused them were as

follows:

1. Exponential growth at the far left of the graph. This represents

   the period of early expansion and commercialization of the former

   research network, from the late 1980s through approximately 1994.

   The major driver for this growth was a lack of aggregation

   capability for transit providers, and the widespread use of

   legacy Class C allocations for end sites. Each time a new site

   was connected to the global Internet, one or more new routing

   entries were generated.

2. Acceleration of the exponential trend in late 1993 and early 1994

   as CIDR "supernet" blocks were first assigned by the NIC and

   routed as separate legacy class-C networks by service provider.

3. A sharp drop in 1994 as BGP4 deployment by providers allowed

   aggregation of the "supernet" blocks. Note that the periods of

   largest declines in the number of routing table entries typically

   correspond to the weeks following each meeting of the IETF CIDR

   Deployment Working Group.

4. Roughly linear growth from mid-1994 to early 1999 as CIDR-based

   address assignments were made and aggregated routes added

   throughout the network.

5. A new period of exponential growth again from early 1999 until

   2001 as the "high-tech bubble" fueled both rapid expansion of the

   Internet, as well as a large increase in more-specific route

   advertisements for multi-homing and traffic engineering.



6. Flattening of growth through 2001 caused by a combination of the

   "dot-com bust", which caused many organizations to cease

   operations, and the "CIDR police" [CPOL] work aimed at improving

   aggregation efficiency.

7. Roughly linear growth through 2002 and 2003. This most likely

   represents a resumption of the "normal" growth rate observed

   before the "bubble", as well as an end to the "CIDR Police"

   effort.

8. A more recent trend of exponential growth beginning in 2004. The

   best explanation would seem to be an improvement of the global

   economy driving increased expansion of the Internet and the

   continued absence of the "CIDR Police" effort, which previously

   served as an educational tool for new providers to improve

   aggregation efficiency. There have also been some cases where

   service providers have deliberately de-aggregated prefixes in an

   attempt to mitigate security problems caused by conflicting route

   advertisements (see Section 12). Although this behavior may

   solve the short-term problems seen by such providers, it is

   fundamentally non-scalable and quite detrimental to the community

   as a whole. In addition, there appear to be many providers

   advertising both their allocated prefixes and all the /24

   components thereof, probably due to a lack of consistent current

   information about recommended routing configuration.

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