[ppml] HD Ratio changes

Anthony DeBoer adb at onramp.ca
Tue Feb 10 19:58:29 EST 2004

William Stucke wrote:
> The Excel spreadsheet quoted by Ian Baker at
>  	http://www.codecutters.org/temp/HD-Ratio.xls
> makes the erroneous assumption that 254 out of every 256 addresses are
> available for any size block, when in fact it's 2 addresses (first and last)
> out of any size block that are unavailable.

On the other hand, if you take a big block and carve it into /29s for
customer subnets, then a quarter of a huge allocation can disappear
into subnet broadcast addresses.  You can't count the number of possible
hosts in a block unless you know how it's subnetted.

And, if you're assigning /32s to customer endpoints, you could use *every*
IP address in a block, so it's possible to beat the single-big-ethernet
limit by two hosts.  :-)

Anthony DeBoer
Onramp Technical Support

More information about the ARIN-PPML mailing list