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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



$ 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


The same calculations are available as a spreadsheet with two pages, one with the table and one with the calculator tool.

Download the Open Office version of the spreadsheet

Download the Excel version of the spreadsheet

 

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