BGP AS Number Exhaustion

Geoff Huston

Research activitysupported by APNIC

March 2003

The Problem The 16 bit AS number field in BGP has

64,510 available values to use in the Internet’s public routing space

Some 30,000 AS numbers have already been assigned by the RIRs

This BGP protocol field will be exhausted at some point in the future

The Solution Use a 32 bit field for this value

draft-ietf-idr-as4bytes-06.txt describes how

This is proposed for publication as an experimental RFC

The Issue At some point we will need to start

testing various transition plans and vendor implementations, set up a new AS number registry, and commence deployment of these extended length protocol objects in BGP

When? Before we run completely out of 16 bit AS

numbers! Need to allow a lead time for testing, deployment

of 4-byte AS BGP implementations and development of appropriate transition arrangements Allow 2 – 3 years to undertake this smoothly

So we’d like to know when we have 3 years to go before we run out of AS numbers

When? A number of views can be used to

make forward projections: The growth of the number of

announced AS’s in the BGP routing table

The rate at which AS number blocks are passed from IANA to the RIRs

The rate at which RIRs undertake assignments of As’s to LIRs and end users

The BGP Routing TableAnnounced AS’s

BGP Table - AS Count

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Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03

BGP Table

The BGP Routing TableGrowth Projections

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-10

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-12

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-14

Exp Projection

Linear Projection

RIR Assignments

Feb 2008 May 2013

IANA AS block Allocations

IANA AS Allocations

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35000

Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

IANA AS Allocations

From the IANA AS number Registry

IANA AS Allocation Projection

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-12

IANA Allocations

Exp Projection

Linear Projection

May 2007 Nov 2010

RIR Assignments

RIR Assignments

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Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

RIR Assignments

From the RIR stats reports

RIR Projection

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-92

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Exp Projection

Linear Projection

RIR Assignments

Feb 2008 May 2013

Combining these views

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90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14

IANA

IANA EXP

IANA Linear

RIR

RIR Exp

RIR Linear

BGP

BGP exp 02

BGP Linear 02

Combined View + differences

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Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03

IANA

RIR Assigned

BGP Announced

NOT assigned

NOT Announced

Observations

RIRs operate with an allocation buffer of around 5,000 numbers

10,000 AS numbers (40% of the assigned AS numbers) are not announced in the BGP table. Is this the result of old AS assignments falling into

disuse? Or recent AS assignments being hoarded? This pool creates uncertainty in 2 byte AS number

pool exhaustion predictions

Announced and Unannounced ASs

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-02

Announced

Unannounced

Unannounced : Announced AS’s

Ratio Unann:Ann

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0.25

0.5

0.75

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1.25

1.5

1.75

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2.25

Oct-96 Oct-97 Oct-98 Oct-99 Oct-00 Oct-01 Oct-02 Oct-03 Oct-04 Oct-05

Ratio Unann:Ann

Trend:unannounced : announced ratio

Ratio Unann:Ann

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0.25

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0.75

1

1.25

1.5

1.75

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2.25

Oct-96 Oct-97 Oct-98 Oct-99 Oct-00 Oct-01 Oct-02 Oct-03 Oct-04 Oct-05

Ratio Unann:Ann

Announced / Unannounced Distribution by Date

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Jan-9

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90

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91

Sep-9

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92

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3

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93

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3

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94

Sep-9

4

Jan-9

5

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95

Sep-9

5

Jan-9

6

May-

96

Sep-9

6

Jan-9

7

May-

97

Sep-9

7

Jan-9

8

May-

98

Sep-9

8

Jan-9

9

May-

99

Sep-9

9

Jan-0

0

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00

Sep-0

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Jan-0

1

May-

01

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3

UnAnnounced

BGP Announced

Distribution by AS Number Range

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1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281

Unassigned

NOT Announced

Announced

Observations

Low AS number ranges have the highest unannounced / announced ratios Reclamation of unused AS numbers in the low

number ranges is likely to be a useful exercise Recent assignments show a 60%

announcement utilization ratio for AS numbers LIR staging point factors Inadequate incentives to return if no immediate

requirement for deployment

Forecast 1 – AS recovery in effect - 2011

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1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

IANA

RIR

BGP Projection

BGP

Unassigned

Unrouted

Forecast2 – No significant recovery – 2009

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1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

IANA

RIR

BGP Projection

BGP

Unassigned

Unrouted

Current AS Forecast

The available AS number pool will exhaust in the timeframe of 2009-2011 if current AS use trends continue2009

no significant reclamation in old AS number space No coordinated effort to increase utilization density of AS numbers

2011 reclamation and increased deployment efficiency