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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
0
2000
4000
6000
8000
10000
12000
14000
16000
Sep-96 Sep-97 Sep-98 Sep-99 Sep-00 Sep-01 Sep-02 Sep-03
BGP Table
The BGP Routing TableGrowth Projections
0
10000
20000
30000
40000
50000
60000
Jan
-90
Jan
-92
Jan
-94
Jan
-96
Jan
-98
Jan
-00
Jan
-02
Jan
-04
Jan
-06
Jan
-08
Jan
-10
Jan
-12
Jan
-14
Exp Projection
Linear Projection
RIR Assignments
Feb 2008 May 2013
IANA AS block Allocations
IANA AS Allocations
0
5000
10000
15000
20000
25000
30000
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
0
10000
20000
30000
40000
50000
60000
Jan
-90
Jan
-92
Jan
-94
Jan
-96
Jan
-98
Jan
-00
Jan
-02
Jan
-04
Jan
-06
Jan
-08
Jan
-10
Jan
-12
IANA Allocations
Exp Projection
Linear Projection
May 2007 Nov 2010
RIR Assignments
RIR Assignments
0
5000
10000
15000
20000
25000
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
0
10000
20000
30000
40000
50000
60000
Jan
-90
Jan
-92
Jan
-94
Jan
-96
Jan
-98
Jan
-00
Jan
-02
Jan
-04
Jan
-06
Jan
-08
Jan
-10
Jan
-12
Jan
-14
Exp Projection
Linear Projection
RIR Assignments
Feb 2008 May 2013
Combining these views
0
10000
20000
30000
40000
50000
60000
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
0
5000
10000
15000
20000
25000
30000
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
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
0
2000
4000
6000
8000
10000
12000
14000
16000
Oct
-96
Oct
-97
Oct
-98
Oct
-99
Oct
-00
Oct
-01
Oct
-02
Announced
Unannounced
Unannounced : Announced AS’s
Ratio Unann:Ann
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
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
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
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
0
100
200
300
400
500
600
Jan-9
0
May-
90
Sep-9
0
Jan-9
1
May-
91
Sep-9
1
Jan-9
2
May-
92
Sep-9
2
Jan-9
3
May-
93
Sep-9
3
Jan-9
4
May-
94
Sep-9
4
Jan-9
5
May-
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
May-
00
Sep-0
0
Jan-0
1
May-
01
Sep-0
1
Jan-0
2
May-
02
Sep-0
2
Jan-0
3
UnAnnounced
BGP Announced
Distribution by AS Number Range
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
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
0
10000
20000
30000
40000
50000
60000
70000
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
0
10000
20000
30000
40000
50000
60000
70000
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