North American Network Operators Group|
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Re: CIDR FAQ
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...