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I had promised a number of people a paper on economics of route filtering, and I haven't quite got it finished yet. However with regard to current whining, I will post some of the numbers from my current work in progress. I would like to encorage anyone that is working with non-cisco routers, that has information on router limits with regards to memory utilization per prefix, I would like to hear from you. Right now my paper is basied with only numbers I have from various members of Nanog, and my personal numbers in my routers. ----- from "Economics of Route Filtering", Jeremy Porter, Feb 1996, unpublished. ----- Current theory is that a large number of backbone routers will overload when more than about 64,000 prefixes are announced into the global backbone. There are currently about 35,000 networks being announced. With providers filtering routes with prefixes longer than 2^18 bits, with allocations remaining between 207.0.0.0 and 223.255.255.255, we have 17 networks of size 2^8, or 17048 networks of size 2^18. This total is less than the 70,000 "doomsday" routing table. The 2^19 filter length also fulfills the recommendation some people have been making of 2048 prefixes per class A space. This gives us with maximum density 4.4 million hosts on the Internet. With 50% utilization we are still talking about 2.2 million new hosts on the Internet. Currently the reserved spaces have not been allocated except for one notable exception which is a large block anyway. Filtering on just the 2^19 limit gives us a total routing table size between 2.6 million prefixes and 5.3 million prefixes. Given current router technology one could estimate an 8 fold growth in router table size to utilize all 5.3 million prefixes. Thus future routers could need 512 megabytes of memory. This is within the realm of today's technology. Now if we decided that we need our current routers to function, filtering on 2^14 out of 64.0.0.0 - 95.255.255.255 will give an additional 16384 prefixes in a worst case allocation. This is just slightly larger than current routers will hold. With moderate levels of aggregation in 207.0.0.0 - 223.255.255.255 and 64.0.0.0 - 95.255.255.255 we should be able to keep current routers under the doomsday limit. -- Jeremy Porter, Freeside Communications, Inc. [email protected] PO BOX 80315 Austin, Tx 78708 | 1-800-968-8750 | 512-339-6094 http://www.fc.net
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