Policy Proposal 2004-2: Additional Documents [Archived]
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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.
$ 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
The same calculations are available as a spreadsheet with two pages, one with the table and one with the calculator tool.
OUT OF DATE?
Here in the Vault, information is published in its final form and then not changed or updated. As a result, some content, specifically links to other pages and other references, may be out-of-date or no longer available.