At 8:47 PM 8/17/95, Gary Wright wrote:
Renumbering isn't necessarily required if the blocks are given out such that there is room for growth should the smaller IP come back for more addresses. For example when I allocate individual class C addresses, I don't give them out consecutively. Initially I leave at least three unused addresses after the one I allocate. If someone comes back and needs more, their allocation grows to fill up the holes. I try to judge who will grow (e.g., a town network) and who won't (a BBS) and leave my options open as long as possible.
One can also accomplish this with a lot less thought by simply making each allocation be as far away from all other allocations as possible within a given CIDR block. For example, allocate xx.xx.0/24 first, xx.xx.128/24 second, xx.xx.64/24 third, xx.xx.192/24 fourth, xx.xx.32/24 fifth, etc. If one only allocates 50% of the space using that kind of an algorithm, then every single prefix can be doubled to become a /23. If one only allocates 25% or the space, then every single prefix can be quadrupled to become a /22. Of course, we'd have to convince the authorities that 25% to 50% utilization of a CIDR block in this manner is a good thing so we could get new /16 or bigger blocks...
One can also accomplish this with a lot less thought by simply making each allocation be as far away from all other allocations as possible within a given CIDR block. For example, allocate xx.xx.0/24 first, xx.xx.128/24 second, xx.xx.64/24 third, xx.xx.192/24 fourth, xx.xx.32/24 fifth, etc.
If one only allocates 50% of the space using that kind of an algorithm, then every single prefix can be doubled to become a /23. If one only allocates 25% or the space, then every single prefix can be quadrupled to become a /22.
Of course, we'd have to convince the authorities that 25% to 50% utilization of a CIDR block in this manner is a good thing so we could get new /16 or bigger blocks...
Which is the entire problem. We go through about 512 Class C's in roughly 6 weeks (at least last time I checked). The InterNIC won't give out more CIDR blocks until we have utilized 90% or more of our blocks (read that swipped). We get a /15 prefix from the NIC, and in 6 weeks, it's 100% assigned, and within 8 weeks of the initial assignment, 95% of the entire block is routing. What I would rather do, is chop everything into little bits by relative location to a NAP, and summarize a huge CIDR block with a specific MED (for those that will take it). Then, it doesn't matter how message my core get's with /22's, everything looks clean from the outside. Dave -- Dave Siegel Director of Engineering, Net99 http://www.webcity.com/ (602)249-1083 24x7 NOC line http://www.rtd.com/~dsiegel/ (520)318-0696 My Tucson Office
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