Re: CIDR FAQ

[Dave Siegel <dsiegel () net99 net>]

> 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