On Sat, 2010-07-24 at 14:07 -0500, Jack Bates wrote:
The chance that any random prefix will conflict with any chosen prefix is very, very small. The chance that two conflicting prefixes would belong to entities that will ever actually interact is even smaller. Makes it an interesting question as to whether the managed range is really necessary at all.
1) While the chance of conflict is small, it is not non-existent, and when the interaction does occur and a conflict does arise, there may be huge costs involved. Random is fine for small deployments. It is a horrifying prospect for a 500+ subnet network.
If two (or four, or ten, or a thousand) ULA prefixes are chosen randomly, the chance that any will conflict with any others is far, far less than the chance that your staff will make a terrible, disastrous mistake that puts you out of commission for weeks. And if you happen to have contingency plans for that, they will do just fine for dealing with a ULA conflict.[1] And of course, to be an actual problem the conflicting prefixes have to be in use by entities whose networks actually interact. Within an administrative domain, uniqueness can be guaranteed anyway. Winning a lottery is *far* more likely[2] than that a randomly chosen prefix from the ULA range will conflict with any other prefix in the same range, randomly chosen or not. Regards, K. [1] A ULA conflict is generally not going to require instant remedial action. People planning interaction at a network level will (one hopes!) do basic stuff like checking what prefixes are in use on the two networks. [2] Depending on the number of "players" in each "game", anything from hundreds of times more likely to millions of times more likely. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Karl Auer (kauer@biplane.com.au) +61-2-64957160 (h) http://www.biplane.com.au/~kauer/ +61-428-957160 (mob) GPG fingerprint: B386 7819 B227 2961 8301 C5A9 2EBC 754B CD97 0156 Old fingerprint: 07F3 1DF9 9D45 8BCD 7DD5 00CE 4A44 6A03 F43A 7DEF