Dick says (with a smile):
I'm just a country network jockey and don't understand all this stuff,
Here is a very simple explanation for you to "take to the bank"; and I'll avoid discussing any particular provider and look at the generic question only. First, pull up your favorite browser and look at this simple diagram from an excellent 1977 paper by Kleinrock and Kamoun [1]: http://www.silkroad.com/public/K&K-ComputerNetworks-77-fig-1.gif Now, consider this model a very simplified model of the Internet. Notice that for purposes of discussion, K&K used a 3-level clustered 24-node network; but the theory scales upward. In fact, image that YOU are a provider at the 3rd level of the network and that the network is expanding rapidly and your routing tables are about to overflow. What must you do to remain at your place in the hierarchy? One obvious way is to create more clusters of route aggregation and form another level in the hierarchy and the 3-level clustered model becomes a 4-level cluster. Without getting into the details, even us Tulane 'bare-foot country networkers :-) " can see that the optimal goal of a provider at each layer is to accept routing information from networks that are only 1 level less than their position in the hierarchy. Of course, there are numerous other variations to the them, but the end results are basically the same. To illustrate this, please take a final browse at another figure from Kleinrock and Kamoun [1]: http://www.silkroad.com/public/K&K-ComputerNetworks-77-fig-2.gif This diagram is just K&K figure 1 illustrated in a tree. As a side note, please understand that hierarchical routing is not a new concept. In fact the original concept of classful A, B, and C IP address space was basically the same model, where individual clusters in the network were originally either a /8 or a /16 or a /24; and the network was somewhat simpler and more closely resembled a symmetric model. Back to Fig. 2; please note that with the implementation of classless address space, the model becomes much more complex and a drawing of the Internet is much more complex; but what remains the same is the fact that as the network grows, you can easily understand (and think for yourself) why certain providers have particular business policies for connecting to their network or why "things are the way they are", in a simple matter of speaking. Furthermore, providers that the highest levels of the hierarchy have a very difficult task considering that they did not have the privilege to manage the address space in the during the early days of the Internet. In fact, as many people know, many remain incredulous to the fact that the original funding agency may have mismanaged the commercialization of the original IP network (but I'll omit the details). Understandably, it was difficult to take the fragmented IP address space model and create an environment that would allow an easy transition from a non-commercial use policy to uncontrollable commercial growth. But, on the other hand, taking a "hands off, anything goes, turn the keys over to commercial providers" approach...... I think historians will find that the study of this transition and the subsequent business climate and problems very interesting (as the concept of hierarchical routing becomes second nature to the layman). I would like to acknowledge the members of the CIRD-WG within the IETF for pointing me into the direction of the archives of Computer Networks and in particular the papers of K&K, with special thanks to Noel Chiappa for the pointer and UCLA for a copy of the original Kleinrock paper. In addition, in respect to one of the authors, Professor Kleinrock, I would like to say thank you for such outstanding work in the field. I look forward to your 1996 publications of _Queuing Systems_ by John Wiley and Sons. Also, thank you for your patience with my use of the southern vernacular. Best Regards Tim [1] Kleinrock, L. and Kamoun, F., "Hierarchical Routing for Large Networks", Computer Networks, Vol 1, No. 3, 1977, p. 155-174. +------------------------------------------------------------------------+ | Tim Bass | | | Principal Network Systems Engineer | "... images are the literature | | The Silk Road Group, Ltd. | of the layman." | | | | | http://www.silkroad.com/ | Umberto Eco | | | | +------------------------------------------------------------------------+