BGP ASN exhaustion
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The document discusses the impending exhaustion of the 16-bit AS number field in BGP. It analyzes historical data on IANA allocations, RIR assignments, and announced ASNs in BGP to project exhaustion between 2009-2011. While 30,000 ASNs have been assigned, only around 20,000 are currently announced in BGP. Reclaiming unused low ASNs and increasing deployment efficiency could extend the lifetime to 2011, otherwise exhaustion may occur as early as 2009. A transition to 32-bit ASNs is proposed.
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BGP ASN exhaustion
- 1. BGP AS Number Exhaustion Geoff Huston Research activity supported by APNIC March 2003
- 2. 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
- 3. 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
- 4. 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
- 5. 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
- 6. 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
- 7. The BGP Routing Table Announced 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
- 8. The BGP Routing Table Growth 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
- 9. 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
- 10. 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
- 11. 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
- 12. 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
- 13. 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
- 14. 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
- 15. 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
- 17. 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
- 18. 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
- 19. Announced / Unannounced Distribution by Date 0 100 200 300 400 500 600 Jan-90 May-90 Sep-90 Jan-91 May-91 Sep-91 Jan-92 May-92 Sep-92 Jan-93 May-93 Sep-93 Jan-94 May-94 Sep-94 Jan-95 May-95 Sep-95 Jan-96 May-96 Sep-96 Jan-97 May-97 Sep-97 Jan-98 May-98 Sep-98 Jan-99 May-99 Sep-99 Jan-00 May-00 Sep-00 Jan-01 May-01 Sep-01 Jan-02 May-02 Sep-02 Jan-03 UnAnnounced BGP Announced
- 20. 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
- 21. 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
- 22. 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
- 23. Forecast 2 – 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
- 24. Current AS Forecast The available AS number pool will exhaust in the timeframe of 2009-2011 if current AS use trends continue 2009 no significant reclamation in old AS number space No coordinated effort to increase utilization density of AS numbers 2011 reclamation and increased deployment efficiency
Editor's Notes
- This work is looking at the trends in consumption of the AS number pool in the Internet The AS number pool of 65536 numbers has 64.510 non-reserved numbers Currently the AS number pool is around 48% allocated. The question is how long will the remaining 52% last in terms of meeting Internet demands and what should we do when we get close to exhaustion
- The technical solution developed in the IETF is to extend the AS number field to 32 bits. This solution has been developed in the Inter Domain Routing Working Group of the IETF and is documented in the draft. This draft is on track for publication as an experimental RFC
- Transition cannot be undertaken in an instant. A prudent approach to this requires examination of transition plans, as well as testing of various vendor implementations for operational reliability and interoperability. Also there is a requirement for a new registry, and associated processes for deployment.
- How long would this pre-deployment phase take the global Internet industry? Estimates are difficult to make, but in considering allowing time for testing, experimental deployments, and completion of transition plans a 2 – 3 year timeframe does not appear unreasonable. So its reasonable to conclude that it would be useful to know when we have around 3 years prior to pool exhaustion of the 16 bit number space, and particularly useful to know if the three year time is some time in the immediate future!
- Lets look at ways to determine forward projections of AS number use. There are three sources of data regarding AS number use. The first is the number of ASes announced in the global BGP routing table. However there are two other data sources that are also relevant to this question: the rate at which AS number blocks (a block size is 1024 numbers) are passed from IANA to the RIRs and the rate at which RIRs undertake assignments to LIRs and end users
- The number of Ass announced in the routing table is shown here. The circled point appears to be an inflexion point corresponding to the end of the Internet boom
- From this data there are two potential growth curves. The pre-2002 data was showing a strong exponential growth trend, with AS number exhaustion appearing in late 2005. The 2002 – 2003 data can be fitted to both a linear and an exponential growth curve. An exponential growth curve would see exhaustion in around 10 years from now in 2013, and a linear trend would see exhaustion occurring in 25 years, in around 2027
- The IANA block allocation data does not have the same point of inflexion, and shows a more consistent growth pattern that appears to have an exponential component.
- Using the same 2002-2003 data as the base line there are again 2 possible trends: an exponential trend would see exhaustion of the IANA pool in 4 years from now (2007) and a linear trend would project exhaustion in 7 years (2010)
- This data is based on the RIR stats files, which show the data of assignment. Here there is also a point of inflexion, although not as pronounced as in the BGP table.
- Again taking 2002-2003 data and extrapolating forward, the exponential trend predicts exhaustion in 5 years time (2008) and the linear trend sees exhaustion in 2013
- This graph shows all three data sets and their projections
- The process here is that a number block is passed from IANA to the RIRs, and the RIRs undertake assignments to LIRs and end users, and, ultimately the AS numbers are advertised in the routing table. The orange jagged line shows the amount of AS numbers held by the RIRs pending assignment. With 4 RIRs active the pool of AS numbers held by the RIRs is currently steady at 5000 The red line shows the number of assigned ASes that are not advertised. This number is increasing, and is currently 10000
- This pool of 10,000 unannounced AS numbers is interesting, and as the slide indicates there are a number of reasons why there are so many unannounced ASes
- This graph shows the number of announced (blue) and unannounced (green) ASes The question is whether the ratio of announced : unannounced is constant or changing…next slide
- The ratio was historically high. In 1996 it appears that two thirds of assigned AS numbers were not visible in the BGP routing table. This has been reduced to the current ration of 0.7, which has been relatively stable for the past 1 ½ years (with a slight growth component – next slide)
- A slight growth pattern is visible in this ratio at present.
- This shows the AS ordered by date of assignment as listed in the RIR stats files. There is a strong peak visible in the 2001 timeframe and, interestingly, another peak at the start of 2003.
- This graph orders the ASes numericall in groups of 100. The rationale for this is that, in general, AS numbers have been assigned in numerical order, and the smaller valued numbers have been in circulation for a longer period. The green shows the number of ASes in each block that have been returned to the RIR or nopt yet assigned by the RIR. The red shows the number of ASes in each block of 100 that are listed as assigned, but are not visible in the BGP routing table The blue shows assigned advertised ASes. One interpretation of this graph is that: - There is some reclamation of unused ASes, but it ius not significant Older AS numbers have a sigificant propotion of numbers that are in a ‘zombie’ state More recent AS numbers show a 70% advertisement rate.
- We take the three data series (IANA, RIR and BGP table) and place them into a model This model includes an RIR holding pool with a 1024 cycle rate and a median pool value. i.e. whenever the RIR pool falls to 4,500 ASes the IANA pool is decremented by 1024 and the RIR pool is augmented by the same amount. The BGP table is assumed to consume AS numbers at an exponentially growing rate, using the past 18 months data as the trend base for the exponential projection The assumption here is that the ratio of announced to unannounced ASes will decline, and older unused ASes will be recycled. This model predicts exhaustion of the AS number pool in 2011 (8 years from now)
- This model is the same as the previous slide, with the exception that the unannounced AS number pool will remain at a level of 70% of the announced AS number pool – i.e. there is no reclamation of unannounced unused ASes. In this model AS number exhaustion will occur in 2009, 6 years from now.
- Summarizing the information in the previous 2 slides, it appears that there is little benefit in reclamation of unused AS numbers. It also indicates that there is currently a 6 year lifetime in the 16 bit AS number pool. Given the earlier comments about a 3 years industry lead time, it would appear that there is still some time before we need to concentrate effort in transitioning BGP in our deployed networks to versions that will support a larger AS number space.