Policy
Proposal 2004-2: Additional Documents
Supplied by the author, Michael Dillon
First of all, there is the original
definition for the HD ratio in RFC 3194. This documents what
the Host Density Ratio is and has some of the basic rationale for using
such a ratio to evaluate the efficiency of address allocation. The HD
Ratio is now being used as the basic metric for IPv6 allocation efficiency.
In August 2003, Paul Wilson introduced a proposal
to APNIC to suggest that this ratio should be applied to IPv4 addresses
and evaluated the possible impact of introducing this measure. I won't
attempt to repeat all of Paul's points in the ARIN proposal and I strongly
suggest that you should read Paul's proposal for some additional background
on the HD Ratio.
With this type of a proposal, it is useful to look at the data graphically. You can see some charts and some additional information including a clear explanation of the formulas in this brief slide presentation. By going to the slide presentation page, you can either look at the presentation on the web or download it in your choice of Open Office, Powerpoint or PDF format. Some of the slides have notes which are only easy to see in the web and Powerpoint versions.
I have prepared a spreadsheet containing the formulas for calculating the HD Ratio for various sized address blocks and a simple HD Ratio calculator that can be used to investigate the effect on various block sizes. The same calculations have been implemented as PERL scripts which produce output like the following:
| / Num IPs 80% HDR
.966 HDR .930 24 256 204 212 173 23 512 409 414 330 22 1024 819 809 630 21 2048 1638 1580 1200 20 4096 3276 3087 2288 19 8192 6553 6030 4359 18 16384 13107 11779 8306 17 32768 26214 23010 15825 16 65536 52428 44948 30152 15 131072 104857 87804 57449 14 262144 209715 171517 109456 13 524288 419430 335046 208545 12 1048576 838860 654484 397336 11 2097152 1677721 1278481 757034 10 4194304 3355443 2497407 1442360 9 8388608 6710886 4878479 2748094 8 16777216 13421772 9529704 5235877 Press RETURN to continue... / This column is the prefix length as used in CIDR slash notation Num Ips The number of IP addresses in the specified prefix 80% Number of IP addresses marking the 80% threshold HDR .966 When the HD Ratio of the block is .966 it refers to this many addresses HDR .930 When the HD Ratio of the block is .930 it refers to this many addresses Example ------- If you have a /16 equivalent of IP addresses and the last allocation that you received from ARIN was a /19 then you must utilize at least 44,948 addresses in total as well as at least 4,359 addresses from your last allocation. If you meet both of these tests then you have justified a new allocation. The assumption is that your last allocation of /19 brought your total allocation up to exactly a /16. Download the PERL source code |
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| $ perl hdrcalc.pl Enter a number or CIDR block size, i.e. 3072 or /24 /24 24 / This column is the prefix length as used in CIDR slash notation 256 Num Ips The number of IP addresses in the specified prefix 204 80% Number of IP addresses marking the 80% threshold 212 HDR .966 When the HD Ratio of the block is .966 it refers to this many addresses 173 HDR .930 When the HD Ratio of the block is .930 it refers to this many addresses Download the PERL source code |
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The same calculations are
available as a spreadsheet with two pages, one with the table and
one with the calculator tool. |
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