On Tue, 02 Nov 2010 03:46:55 +1030, Mark Smith said:
How about algorithmically generating these addresses, so that they're near unique, instead of having the overhead of a central registry, and a global routability expectation?
Go re-read RFC4193, section 3.2.3: 3.2.3. Analysis of the Uniqueness of Global IDs The selection of a pseudo random Global ID is similar to the selection of an SSRC identifier in RTP/RTCP defined in Section 8.1 of [RTP]. This analysis is adapted from that document. Since Global IDs are chosen randomly (and independently), it is possible that separate networks have chosen the same Global ID. For any given network, with one or more random Global IDs, that has inter-connections to other such networks, having a total of N such IDs, the probability that two or more of these IDs will collide can be approximated using the formula: P = 1 - exp(-N**2 / 2**(L+1)) where P is the probability of collision, N is the number of interconnected Global IDs, and L is the length of the Global ID. The following table shows the probability of a collision for a range of connections using a 40-bit Global ID field. Connections Probability of Collision 2 1.81*10^-12 10 4.54*10^-11 100 4.54*10^-09 1000 4.54*10^-07 10000 4.54*10^-05 Based on this analysis, the uniqueness of locally generated Global IDs is adequate for sites planning a small to moderate amount of inter-site communication using locally generated Global IDs. Works great if you're creating a conglomerate of even a few thousand private networks that would otherwise have been RFC1918 collision city. Global usage is another story. Last week's 'Weekly Routing Table' posting listed 332,569. Feel free to do the computation above for 300K networks and let us know how you'd feel about debugging the resulting routing table.