HD Ratio for IPv4

• You get a new allocation when your entire hoard of IPv4 addresses is sufficiently utilized

• You must pass both HD ratio tests – last allocated block must be >= .930 – total hoard must be >= .966

• HD ratio is log(utilized addresses) divided by log(entire hoard)

What does it mean?Percentage

Slash Num Ips at HD 0.96624 256 82.8%23 512 80.9%22 1024 79.0%21 2048 77.2%20 4096 75.4%19 8192 73.6%18 16384 71.9%17 32768 70.2%16 65536 68.6%15 131072 67.0%14 262144 65.4%13 524288 63.9%12 1048576 62.4%11 2097152 61.0%10 4194304 59.5%9 8388608 58.2%8 16777216 56.8%

New policy kicksin for providerswith /20 or more

Old Thresholdof 80%

What does it mean?

• Benefit increases rapidly as an ISP grows to mid-sized

• Not just for the few big guys

Percentage at HD 0.966

0.0%10.0%20.0%30.0%40.0%50.0%60.0%70.0%80.0%90.0%

0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000

This is the /14 level

What does it mean?Percentage at HD 0.966

each /24 increment from /20 up to /17

69.0%

70.0%

71.0%

72.0%

73.0%

74.0%

75.0%

76.0%

0 5000 10000 15000 20000 25000 30000 35000

• The smaller ISPs will only need between 70% and 75% utilization rates

What does it mean?% Thresholds in /20 increments up to 1/2 million

0

10

20

30

40

50

60

70

80

90

100

4,09

6

20,4

80

36,8

64

53,2

48

69,6

32

86,0

16

102,

400

118,

784

135,

168

151,

552

167,

936

184,

320

200,

704

217,

088

233,

472

249,

856

266,

240

282,

624

299,

008

315,

392

331,

776

348,

160

364,

544

380,

928

397,

312

413,

696

430,

080

446,

464

462,

848

479,

232

495,

616

.966 Threshold

.930 Threshold

/15 size

/20 size current 80% threshold

/13 size

Why, why, why?

• Why do you have to count utilization of all previous blocks?

• Because the HD ratio calculation is meant to recognize that overhead increases as a network grows larger. We need to count the ISP’s entire hoard of IPv4 addresses in order to properly make allowance for this overhead.

Why, why, why?

• Why did you choose .966 for the HD ratio magic number?

• Mainly because I felt that Paul Wilson’s argument made sense in his discussion paper for APNIC http://www.apnic.net/mailing-lists/sig-policy/archive/2003/08/msg00000.html

Why, why, why?

• Why set a separate .930 ratio for the previous allocation?

• This is to simplify ISP planning. When they receive a new block, an ISP can calculate the .930 ratio for it and use this as a target for planning. Only ISPs with significant churn of older addresses will need to closely track the overall .966 ratio.

Why, why, why?

• But why be more lenient with .930 ratio?• We believe that it is prudent for network

operators to have change control processes and we recognize that such processes take time. The .930 ratio demands that ISPs show they are indeed deploying the last allocation but it avoids unnecessary brinkmanship with their change control timing.

Why, why, why?

• Why are you using a complicated natural logarithm?

• A logarithmic ratio is used because that creates a sliding scale that recognizes the sliding scale of overhead inherent in hierarchical allocation of addresses. The natural logarithm was chosen because it is supported by both PERL and Excel.

Why, why, why?

• Why do you care so much about PERL?• While I wish the world would throw away all

PERL code and replace it with Python or Ruby, I recognize that it is a major tool for ISPs and many IP address management packages are written in PERL. Similarly, many small ISPs manage IP addresses using spreadsheets like Excel.

Understanding the formula

• Given a range of IPv4 addresses

• Let utiladdr = the number of IPv4 addresses utilized out of the range

• Let totaddr = the total number of IPv4 addresses in the range

• In Excel: HD = ln(utiladdr)/ln(totaddr)

• In PERL: HD = log(utiladdr)/log(totaddr)

Understanding the Formula• Basic ratio calculation.

Percentage = Part / Whole

Part = Percentage * WholeWhole = Part / Percentage

P

% WInverse

Relationships

+ -

ln() exp()

% - PercentageP - PartW - Whole

Key formulas are marked with

Understanding the Formula• HD Ratio is a ratio just like percentage.

HDRatio = ln(Part) / ln(Whole)

ln(Part) = HDRatio * ln(Whole)ln(Whole) = ln(Part) / HDRatio

ln(P)

HDR ln(W)

exp() inverts ln() Part = exp( ln(Part) )Whole = exp( ln(Whole) )

therefore:Part = exp( HDRatio * ln(Whole) )Whole = exp( ln(Part) / HDRatio )

Key formulas are marked with